B.Sc.II paper VIII Notes

B. Sc. Part II Semester- IV

ZOOLOGY

Paper-VIII

DSC- …….. (APPLIED ZOOLOGY-I)

Theory: 30 hrs. (37.5 lectures of 48 minutes)

Marks-50 (Credits: 02)

Unit 1

Introduction to Host-parasite Relationship, Host, Definitive host, Intermediate host,

Parasitism, Symbiosis, Commensalism, Reservoir, Zoonosis.                                     (4 hrs.)

Unit 2

Epidemiology of Diseases                                                                                                    (7 hrs.)

Transmission, Prevention and control of diseases: Tuberculosis, Typhoid.

Unit 3

Rickettsia and Spirochaetes                                                                                                  (6 hrs.)

Brief account of Rickettsia prowazekii, Borrelia recurrentis and Treponema pallidum.

Unit 4

Insects of Economic Importance                                                                                           (8 hrs.)

Biology, Control and damage caused by Helicoverpa armigera, Pyrilla perpusilla and

Papilio demoleus, Callosobruchus chinensis, Sitophilus oryzae and Tribolium castaneum

Unit 5

Poultry Farming                                                                                                                      (5 hrs.)

Principles of poultry breeding, Management of breeding stock and broilers, Processing and

Preservation of eggs.

UNIT NO. I: INTRODUCTION TO HOST-PARASITE RELATIONSHIP

DEFINITION

In biology and medicine, a host is an organism that harbours a parasitic, a mutualistic, or a commensalist guest (symbiont), the guest typically being provided with nourishment and shelter. Examples include animals playing host to parasitic worms (e.g. nematodes), cells harbouring pathogenic (diseasecausing) viruses,a bean    plant hosting mutualistic (helpful) nitrogen-fixing bacteria.  Due to close contact or intimate association, the responsive reactions and resis­tance displayed by a host to its parasite and the protective devices adopted by a parasite in response to its host’s reactions in order to establish them in their respective environments are called host-parasite-interactions. Parasitism is a very broad term and different types of parasites are recognized on different basis.

In the course of their life cycle, parasite may become associated with more than one host. In many cases the life cycle is characterized by numerous very rigid requirements. Whenever a parasite is able to live and repro­duce within a host the result is an elaborate host- parasite interaction.

TYPES OF HOSTS

1.       Definitive or primary host - an organism in which the parasite reaches maturity and reproduces sexually, if possible. This is the final host.

2.       Secondary or intermediate host - an organism that harbors the sexually immature parasite and is required by the parasite to undergo development and complete its life cycle. It often acts as a vector of the parasite to reach its definitive host. For example, Taenia solium, the tapeworm uses the pig as its intermediate host until it matures into the infective larval stage.

3.       It is not always easy or even possible to identify which host is definitive and which secondary. As the life cycles of many parasites are not well understood, sometimes the subjectively more important organism is arbitrarily labeled as definitive, and this designation may continue even after it is found to be incorrect. For example, sludge worms are sometimes considered "intermediate hosts" for salmonid whirling disease, even though the myxosporean parasite reproduces sexually inside them. In trichinosis, a disease caused by roundworms, the host has reproductive adults in its digestive tract and immature juveniles in its muscles, and is therefore both an intermediate and a definitive host.

4.       Paratenic host - an organism that harbors the sexually immature parasite but is not necessary for the parasite's development cycle to progress. Paratenic hosts serve as "dumps" for non-mature stages of a parasite in which they can accumulate in high numbers. The trematode Alaria americana may serve as an example: the so-called mesocercarial stages of this parasite reside in tadpoles, which are rarely eaten by the definitive canine host. The tadpoles are more frequently preyed on by snakes, in which the mesocercariae may not undergo further development. However, the parasites may accumulate in the snake paratenic host and infect the definitive host once the snake is consumed by a canid. The nematode Skrjabingylus nasicola is another example, with slugs as the intermediate hosts, shrews and rodents as the paratenic hosts, and mustelids as the definitive hosts.

5.       Dead-end, incidental, or accidental host - an organism that generally does not allow transmission to the definitive host, thereby prevents the parasite from completing its development. For example, humans and horses are dead-end hosts for West Nile virus, whose life cycle is normally between culicine mosquitoes and birds. People and horses can become infected, but the level of virus in their blood does not become high enough to pass on the infection to mosquitoes that bite them.

6.       Reservoir host - an organism that harbors a pathogen but suffers no ill effects. However, it serves as a source of infection to other species that are susceptible, with important implications for disease control. A single reservoir host may be reinfected several times.

PARASITISM

Parasitism is a type of symbiotic relationship, or long-term relationship between two species, where one member, the parasite, gains benefits that come at the expense of the host member. The word parasite comes from the Latin form of the Greek word parasitos, meaning “one who eats at the table of another”.

TYPES OF PARASITISM

There are many types of parasitism, and parasites can belong to multiple classifications based on their size, characteristics, and relationship with the host.

1)      Obligate Parasitism

Obligate parasites are completely dependent on the host in order to complete their life cycle. Over time, they have evolved so that they can no longer exist without the existence of the host. This means that they usually will not cause serious harm to the host, as the parasites need the host to survive so that they can survive, unless the host’s death is needed for the transmission of the parasite. Obligate parasitism can be found in many different types of organisms, like plants, animals, fungi, bacteria, and viruses. Head lice are obligate parasites; if removed from the human scalp, they will soon die.

2)      Facultative Parasitism

Facultative parasites do not rely on the host in order to complete their life cycle; they can survive without the host, and only sometimes perform parasitic activities. Certain plants, fungi, animals, and microbes can be facultative parasites. A specific example is the nematode species Strongyloides stercoralis. This is a type of roundworm that can cause the disease strongyloidiasis when it infects humans, but it can also be found free-living.

3)      Ectoparasitism, Endoparasitism, and Mesoparasitism

Ectoparasites are parasites that live on the outside of the host’s body, such as lice and ticks. Endoparasites, like nematodes and hookworms, live inside the host. Mesoparasites enter the host’s external openings, such as the outer ear or the cloaca.

4)      Macroparasitism Versus Microparasitism

Macroparasites are parasites that are large enough to be seen with the naked eye. Microparasites are too small to be seen and must be viewed under a microscope. They are generally unicellular, such as protozoa.

5)      Necrotrophic Versus Biotrophic

Necrotrophic parasites, also called parasitoids, essentially eat part of the host organism’s tissue until it dies from the loss of tissue or from nutrient loss. Biotrophic parasites do not do severe enough damage to kill their host; they need to keep the host alive because they can’t survive in a dead one.

6)      Monogenic Versus Digenetic

Monogenic parasites complete their life cycle in only one individual host. Digenetic parasites need more than one host to complete their life cycle. Plasmodium vivax, the protozoa that carries malaria, is digenetic. In order to complete its life cycle, it must be a parasite of both people and mosquitos.

7)      Epiparasitism

An epiparasite is a parasite that parasitizes another organism that is also a parasite. Epiparasites are also called hyperparasites or secondary parasites. One example would be a protozoan living in a flea that is living on a dog.

8)      Social Parasitism

Social parasites take advantage of social insects like ants, bees, and termites. They may use mimicry to invade the hive. Some bumblebees invade the hives of other species of bees, making that species raise the parasite’s young. One ant species, Tetramorium inquilinum, is a parasite that spends its entire life on the back of other species of ants, essentially making the host species its slaves. This parasite species has gained benefits such as food and transportation, but from this extreme form of parasitism the ants have evolved to be so weak that if they fall off their host, they will not be able to crawl back on, and die.

9)      Brood Parasitism

Brood parasitism involves the raising of young. Bird species that practice brood parasitism, including cowbirds and cuckoos, lay their eggs in another species’ nest instead of building their own nests. This is a form of parasitism because the species who lay their eggs in other nests gain benefits (they don’t have to spend energy raising young) while the other species are harmed (they do have to use energy to raise young, and it is not their genetic material). Sometimes, the parasite species will even kick the other species’ eggs out of the nest, forcing the host to raise only the parasite’s young. Brood parasitism can also occur in fish. It is a type of kleptoparasitism, which involves directly or indirectly taking food from the host; in this case, food that could have gone toward the host species goes to the parasite species instead. This photograph shows brood parasitism. A brown-headed cowbird has laid its speckled egg in the nest of an Eastern phoebe.

EXAMPLES OF PARASITISM

Over half of all organisms on Earth have a parasitic phase at some point in their life cycle, so there are many examples of parasitism besides the ones already mentioned and the ones listed below.

1)      In Humans

Over 100 different types of organisms can parasitize humans including fungi, leeches, lice, ticks, mites, tapeworms, protozoa, viruses, and helminths. Helminths are worms that can live inside the intestines and can reach meters in length. They can cause a variety of problems such as malnutrition, jaundice, diarrhea, and even in severe cases, death. However, they can be treated with anti-parasitic medication. All infectious diseases, including the common cold, result from organisms that parasitize humans, such as viruses and bacteria. Many of the organisms that parasitize humans can also parasitize other mammals and birds.

2)      In Plants

Aphids are small green insects that parasitize plants by eating their sap. Many types of fungi can also attack plants and can spoil wheat, fruit, and vegetables. Some plants are parasitic themselves. In angiosperms (flowering plants), parasitism has evolved at least 12 separate times, and 4100 species (about 1%) of angiosperms are parasitic. Parasitic plants have haustoria, which are modified roots which connect to the host plant’s xylem or phloem and drain it of water and nutrients. Some plants parasitize mycorrhizal fungi. This often happens when a plant species has evolved to no longer produce chlorophyll. Since it can no longer photosynthesize, it must gain nutrients for energy in other ways.

3)      In Insects

Entomophagous parasites are insects that parasitize other insects. Usually these parasites attack larva, or young insects. Some insects deposit their eggs within the body of another insect species’ larva; when the eggs hatch, the parasitic young kill and eat the larva, gaining nutrients from it. Sometimes, the parent parasite paralyzes a host which is then fed on by the young. This occurs commonly in wasps such as Ampulex compressa, whose young eat paralyzed cockroaches that have been stung by the parent. Other wasps like Ropalidia romandi burrow into the abdomen of their host and then live there. They do not kill their host, but can change its appearance and behavior, and even make it sterile. Parasitism is extremely common in insects. In fact, almost all species of insects are attacked by at least one type of insect parasite.

4)      In Fish

There are many organisms that parasitize fish, and sometimes different populations of the same species of fish living in the same region can be told apart because they have different characteristic parasites. Some parasites, such as copepods (small crustaceans), nematodes, and leeches. attach to the fish’s gills and live there. Cymothoa exigua is an isopod (another type of small crustacean) that parasitizes fish. It enters a fish’s mouth and eventually severs the fish’s tongue. Then, the isopod itself lives where the tongue was, and becomes the new tongue. The host fish can still eat, and will survive with an isopod in its mouth, but the isopod consumes a small amount of the fish’s blood and mucus while living there. Cleaner fish like bluestreak cleaner wrasses remove dead skin and parasites from other fish, including large predatory fish that would otherwise eat them. Fish parasites in can be a concern to human health when people eat foods that contain uncooked fish, such as sushi, because the parasites in these fish can also infect humans. However, infection through eating uncooked fish is relatively rare in the developed world, and some raw fish is frozen overnight to prevent infections.

RELATED BIOLOGY TERMS

1. Obligate Parasite – A parasite that depends on the host in order to complete its life cycle.
2. Facultative Parasite – A parasite that does not depend on a host can be free-living.
3. Parasitoid – An insect parasite that ultimately kills its host.
4. Protozoa – Single-celled eukaryotic organisms that can move around and prey on other organisms; some species are parasites.

 HOST PARASITE RELATIONSHIP

            When a parasite gains access to a host, the host has to compromise, and the parasite has to adopt itself in host environment. In this way host and parasite establish a sort of relationship which effects each other’s growth, metabolism, etc.

            In general the series of events that constitutes the relation of host and parasite may be considered as beginning with the transmission of parasite from one host to another, then follows the distribution and localization of parasite on or within the host, then growth or multiplication of parasite, the resistance of host to the parasite and the parasite to the host. The method of attack of parasite, changes in host brought about by parasite and those in parasite due to residence in host. Host parasite adjustments during the infection, the escape of infective stages of the parasite from the host and then the recovery or death of host.

HOST-PARASITE RELATIONSHIP STRATEGY

In the host-parasite relationship, we can identify two categories of bio-physiological function. These are:

1. Parasite invasiveness which is aimed to obtain entry into the host and continue its life within the host

2. Host resistance which tends to prevent the invasion of parasite and its colonization. In a host-parasite relation we can see that both these functions counter each other thereby acting as a check to maintain balance in the host parasite relationship.

3. When a parasite is growing and multiplying within or in a host, the host is said to have an infection.

HOST - PARASITE RELATIONSHIP

            From the definition of parasitism it is clear that it involves 2 partners, a parasite and a host and also that parasitism effects both the partners. Host Parasite relationship is defined as the influence of each partner by the activities of the other. In general the host-parasite relationship can be studied under two heads:

A. EFFECTS ON THE PARASITE  B. EFFECTS ON THE HOST

A. EFFECTS ON THE PARASITE

            Effects of parasite on the host are more obvious than those which operate in the reverse direction, but the later are nonetheless important. The general constitution of the host may profoundly influence the host-parasite relationship. The parasite besides undergoing several modifications called parasitic adaptations to survive in the hostile atmosphere in the host has several specific effects on it as-

1. EFFECT OF NUTRITION

            The kind of nutritive material ingested by parasites effects their development. A diet consisting largely of milk has an adverse effect on intestinal helminths or protozoan fauna, because it lacks p-aminobenzoic acid which is necessary for the parasite growth. A high protein diet has been found to be unfavourable for the development of many intestinal Protozoa. On the other hand, a diet low in protein favours the appearance of symptoms of amoebiasis.

            It has also been shown that carbohydrate rich diet favours the development of certain tapeworms. In fact the presence of carbohydrate in the diet is known to be essential for some of the worms.  The nutritional status is of an increased importance both in determining whether or not a particular infection will be accompanied by symptoms and in influencing their severity if present. Nutritional disturbances may also influence resistance through its effects upon the immune mechanisms of the host.

2. EFFECT OF HORMONES

            Hosts hormones have direct effect on the growth and in many cases sexual maturity of parasites e.g., Ascaridia galli attains greater lengths in hyperthyroid chickens whereas Heterakis gallinae attains greater length in hypothyroid host, the two worms apparently respond differently to the hormone thyroxin.

The dog nematode Toxocara canis develops into adult only in the female dogs i.e., bitches, during their pregnancy as hosts sex hormones are necessary for its maturity and growth.

3. EFFECT OF HOST AGE

            Human schistosomes usually infect young persons, and adults over thirty generally do not become infected on exposure. Age resistance does not appear to depend on immune reactions but rather to changes in the host tissues that render them as unsuitable environment for the parasite.

4. EFFECT OF IMMUNITY

            The host produces one or more substances known as antibodies that are chemically antagonistic to the parasite or its products. These antibodies may stunt the growth of the parasite or kill it or prevent its attachment to the host tissues or they may precipitate or neutralize parasitic products.

            Primary infection with Leishmania seems to confer a degree of immunity to reinfection while many protozoal and helminthic infections confer no long lasting immunity to reinfection. They do seem to stimulate resistance during the time that the parasites are still in the body. This resistance to hyperinfection is known as premonition.

5. EFFECT OF HOST SPECIFICITY

            The host specificity varies greatly among helminths. Even closely related helminths may exhibit great differences in host requirements. It is usually supposed that a helminth requires a very specific environment complex for its development and this is found only in proper hosts.

6. EFFECT OF PARASITE DENSITY

            When a number of helminths of one species is present in one host, the worms are usually stunted and of low reproductive capacity. This stunting effect seems to result not from insufficient food supply but from some action of the parasites on each other.

7. EFFECT OF HOST SEX

            An influence of host sex is evidenced in the development of some helminths e.g., Cysticercus fasciolaris is more frequent in male than in female rats, as a consequence of the action of sex hormones; gonadectomy lowers the resistance of females and increases that of males to infection, and injection of female hormones into males also increases the resistance of the latter, whereas injection of females with male hormones lowers their resistance to the Cysticercus.  Also Toxocara canis develops only in pregnant bitch and not in males and others.

B. EFFECTS ON THE HOST

            Sometimes the parasites bring about some changes within their hosts that may be interpreted as affecting the host’s welfare. It is necessary to give some consideration to types and degrees of changes caused by the parasitic animals.

            In classifying the various types of effects, one should remember that in a number of cases multiple effects may be present and it is often not possible to state that a given parasite causes only one specific type of effect. Furthermore, the types of effects often merge into each other so that sharp lines of demarcation between types cannot always be recognised. With our advanced knowledge of host-parasite relations it is increasingly apparent that in many instances it is extremely difficult if not impossible to distinguish between a true parasite and a commensal, because the effect of parasite in some cases may be so minute that it can hardly be considered injurious. However, some classical types of parasite inflicted effects on the host can be sighted:

1. UTILIZATION OF HOST’S FOOD

            Utilization of host’s food to a detrimental point by a parasite is probably the first kind of damage that comes one’s mind. Although in the past some biologists had doubts as the impact of parasites in this regard, since the amount of food microscopic parasites can utilize seems to be negligible. But recent physiological studies of nutritional requirements especially endoparasites have indicated that they robe the host of a good amount of nutrition resulting in serious consequences. Diphyllobothrium latum (Dibothriocephalus latus) in man has been known to cause an anemia similar to pernicious anemia, because of the affinity this tapeworm has for Vitamin B12. This tapeworm can absorb 10-50 times as much vit. B12 as other tapeworms. Since B12 plays an important role in blood formation, its uptake by D. latus causes anemia. Studies of cestode nutritional requirements show that tapeworms not only simple sugars but also nitrogen containing amino acids from the host.

2. UTILIZATION OF HOST’S NON-NUTRITIONAL MATERIALS

            In some cases parasites also feed on host’s substances other than nutrients. The endo- and ecto-parasites that feed on the hosts’ blood are examples. The exact amount of blood utilized by these parasites is difficult to measure during the survival in the host. Approximately e.g., due to blood feeding parasitic hookworms, the haemoglobin may drop 30% below normal.

            It is obvious that the blood lost through parasitic infections can become an appreciable amount over a period of time. Lepage (1958) estimated that 500 hookworms can remove 250 cc of blood (1/24th of the total volume of blood) each day. This estimate may be too high, for others estimate that no more than 50 cc of blood is removed. Nevertheless, the loss of even 50 cc of blood per day constitutes a serious drainage of blood cells, haemoglobin and serum.

3. DESTRUCTION OF HOST TISSUE

             Not all parasites are capable of destroying the host’s tissue, and even among those that do so; the gradation in the degree of damage is large. The parasites destroy the host’s tissue in two ways:

(a) Some parasites destroy (injure) the host’s tissue when they enter the host, and

(b) Others inflict tissue damage after they have successfully entered.

A combination of these two types of injury may occur.

            The hookworms – Necator americanus & Ancylostoma duodenale exemplify the first instance, for the infective larva of the nematodes do extensive damage to cells and underlying connective tissue during penetration of the host’s skin.

            Amoebic dysentery, caused by Entamoeba histolytica, actively ingest the epithelial cells lining host’s large intestine, causing large ulcerations that are not only damaging in themselves but also serve as sites for secondary infections.

            During migration of larvae of the large nematode Ascaris lumbricoides within its host, these larvae pass through the lungs of the host, as a result of the migration of a large number of worms, damage sometimes is due to the lung tissue.

            Histopathological studies of parasite damaged tissues reveal that cell damage other than removal by ingestion or from mechanical disruption is of three major types:

1. Parenchymatous or albuminous degeneration occurs when the cells become swollen and packed albuminous or fatty granules, the nucleus, becomes indistinct, and the cytoplasm becomes pale. This type of damage is characteristic of liver, cardiac muscles and kidney cells.

2. Fatty degenerations, describes the conditions in which the cells become filled with an abnormal amount of fat deposits that give them a yellowish appearance. Hepatic cells display this type of degeneration which are in contact with the parasites.

3. Necrosis occurs when any type of cell degeneration persists. The cells finally die giving the tissue an opaque appearance. In the encystment of Trichinella spiralis in striated muscles, necrosis of the surrounding tissue is followed by calcification.

4. ABNORMAL GROWTH

            One of the possible consequences of parasitism associated with cell and tissue parasites is a change in the growth pattern of the affected tissue. Some of these are serious changes, whereas others are structural and have no serious systemic importance to the whole organism. Such changes can be broadly divided into four main types:

(a) Hyperplasia (Increase in the rate of cell division)

             It is an accelerated rate of cell division resulting from an increased level of cell metabolism. This results to a greater total number of cells, but not necessarily an increase in their absolute size, e.g., the presence of trematode Fasciola hepatica in bile ducts is known to effect rapid division of the lining epithelial cells. The eggs of Schistosoma haematobium with their spiny projections are known to irritate the transitional epithelium of human urinary bladder causing hyperplasia. The presence of the protozoan Eimeria steidae is known to cause hyperplasia in the hepatic cells of rabbit.

(b) Hypertrophy (Increase in cell size)

            This condition is commonly associated with intracellular parasites e.g., during the erythrocytic phase of Plasmodium vivax, the parasitized red blood cells are commonly enlarged.

(c) Metaplasia (Transformation of one type of tissue into another)

            Metaplasia describes the changing of one type of tissue into another without the intervention of embryonic tissue. When the lung fluke – Paragonimus westermani parasitizes man and carnivores, the normal cuboidal cells lining the bronchioles commonly undergo both hyperplasia and metaplasia and are transferred to stratified epithelium.

(d) Neoplasia (Cancer or tumour formation)

            It is the growth of cells in a tissue to form a new structure, for example, a tumour. The neoplastic tumour: (i) is not inflammatory, (ii) is not required for the repair of organs, & (iii) does not conform to a normal growth pattern. Neoplasms may be benign or malignant.

Hyperplasia resulting from parasitic infections may result in neoplastic reactions i.e., the development of tumors from existing tissues, other known instances of neoplasm development include adenoma formation and papilloma which is caused by Schsitosoma mansoni eggs in the colon of man. The liver fluke Opisthorchis sinensis has been suspected of initiating cancer in the liver of man, the lung fluke Paragonimus westermai has been suspected of contributing to cancer in the lungs of tigers.

5. EFFECT OF TOXINS, SECRETIONS, EXCRETIONS, POISONS ETC.

            Specific toxins or poisons, egested, secreted or excreted by parasites have been cited in many cases as the cause of irritation and damage to hosts.

Example of irritating parasite that elicits an allergic reaction in the host is that of Schistosoma cercaria which causes cercarial dermatitis. The severe inflammatory reaction of the host tissue strongly suggests that the fluke secretes some substances that causes the inflammation and indeed such a secretion is now known to exist.

In case of blood sucking insects such as mosquitoes, the swelling resulting from the bites represent the host’s response to the irritating salivary secretions of the insect.

6. MECHANICAL INTERFERENCE

            Less is known about the injuries to the host resulting from mechanical interference by parasites. According to Cheng (1964) they are more common than generally supposed.

The best known case of the type of damage is elephantiasis. In persons infected with the filarial nematode Wucheraria bancrofti, the adult worms become lodged in the lymphatic ducts and thus obstruct the lymph into abnormal channels resulting in the swelling of affected parts, thus causing elephantiasis.

Mechanical damage by nematode is also demonstrated by Ascaris lumbricoides in the intestine and bile ducts of their host. This intestinal parasite which measures up to 14 inches in length, when person in large numbers, can easily block the normal flow of bile down the bile duct and the passage of chime into the intestine.

7. BIOLOGICAL EFFECTS IN THE HOST (Sex reversal) Other interesting and challenging aspect of host parasite relationship are the biological effects on the host. Among the most important and interesting of these are the secondary manifestations resulting from damage to the specific organs. Giard and Smith have shown that in crabs parasitized by Sacculina, the host’s genital tissue is invaded by this crustacean causing drastic changes in males, but not in females. 70% of the parasitized male crabs undergo degeneration of testes and acquire secondary female characteristics. This was found to be true also of ovarian tissue in parasitized females, thus an infected female crab acquires male characteristics. Hence there is a complete loss of sexual dimorphism. However, if the parasites are removed, female acquires normal ovaries but the males’ originally atrophied testis develop into ovotestes capable of producing both the eggs and the sperms. Such an effect on the host due to the parasite is termed as parasitic castration. There have been many studies of Sacculina because this unique crustacean parasite is known to affect the metabolism and sex-life of its host.

8. HOST TISSUE REACTION

            In instances of host tissue reaction, certain host cells and cell products aggregate around the invading parasite forming what is commonly known as host cyst, although cysts are not always of host origin e.g., when the metacercaria of the yellow grubs, Clinostomum marginatum encysts in the skin of fish, two cyst walls are formed around the parasite. The inner one is secreted by the parasite, the outer one is laid down by the host in response to the parasitic invasion. Although the double wall of Trematode metacercarial cysts is a common occurrence, single walled cysts also occur.

9. IMMUNITY TO THE PARASITE

            Majority of the hosts build resistance or immunity against the parasite and they show no visible effects. Immunity may be natural or acquired by previous infections.

Parasitism often becomes an elaborate compromise between the parasite and the host. The parasite harmonizes itself to the habitat and the host protects itself by formation of antibodies and by increasing its efficiency for repair of tissues. This delicate adjustment between the host and the parasite is very common but if it is lacking; then either the parasite fails to survive or the host injured and destroyed.

C) HOST-PARASITES SPECIFICITY

In mature condition a given parasite is quite often found in limited number of hosts. In extreme condition, distribution of a parasite may be restricted to a single host—mono-specific parasite. Even when poly-specific the different hosts are phylogenetically related. This host specificity is a function of physiological specialization and evolutionary age. It is broadly divided into two parts (a) Ecological specificity (b) Physiological specificity

(a) ECOLOGICAL SPECIFICITY

The parasites are capable of making room in a foreign host but normally never reach another host due to ecological barriers. Such parasites are able to develop in more host-species under labora­tory conditions than in nature.

(b) PHYSIOLOGICAL SPECIFICITY

The parasites are physiologically incapable of surviving and reproducing in a foreign host, e.g., Taenia solium in dog survives but never achieves reproductive ability. If the parasites find the conditions suitable for their development then it is said to be compa­tible with that of the host. If not, it is said to be incompatible.

D) IMMUNOLOGICAL INTERACTION BETWEEN HOST AND PARASITE

As the host has immune system which has efficiency to destruct the parasites by producing antibodies (IgG, IgE, etc.) against the specific parasites or their products. Host’s Immune system usually performs Antigen-Antibody reactions, such as toxin neutralization, Agglutination, Precipitation, Lyses, Compliment fixation, Increased Phagocytosis (Opsonification) & allergic sensitization. With the help of these host can resist against the parasite or can destroy it.

            Parasites also have evolved mechanisms to evade their host’s immune systems. Usually the mechanisms used by parasites for defending them against the host response are: Induce Immunosuppressions, Becoming hypoantigenic, Change their surface antigens rapidly & repeatedly (e.g., Trypanosoms rhodiense, T. gambiense), Becoming functionally non-antigenic (T. theileri, T. lewis), Mimicry of host antigens, Adsorption of host antigens (Schistosoma mansoni), Antigenic variation and blocking antibodies.

SYMBIOSIS DEFINITION

A symbiosis is an evolved interaction or close living relationship between organisms from different species, usually with benefits to one or both of the individuals involved. Symbioses may be ‘obligate’, in which case the relationship between the two species is so interdependent, that each of the organisms is unable to survive without the other, or ‘facultative’, in which the two species engage in a symbiotic partnership through choice, and can survive individually. Obligate symbioses are often evolved over a long period of time, while facultative symbioses may be more modern, behavioral adaptions; given time, facultative symbioses may evolve into obligate symbioses.

Endosymbiosis is a symbiotic relationship, occurring when one of the symbiotic partners lives within the body of the other. Endosymbiosis can take place either within the cells (intercellular symbiosis) of the ‘host’ organism, or outside the cells (extracellular symbiosis). On the other hand, ectosymbiosis is a symbiotic relationship in which one organism lives on the body surface of the host, including the lining of the digestive tract, or exocrine glands such as mucus or sweat glands.

TYPES OF SYMBIOSIS

1)      MUTUALISM

Mutualisms are a form of symbiosis in which both symbiotic partners benefit from the interaction, often resulting in a significant fitness gain for either one or both parties. Mutualisms can take the form of resource-resource relationships, service-resource relationships, or service-service relationships.

Resource-resource mutualisms (also known as ‘trophic mutualisms’) happen through the exchange of one resource for another between the two organisms involved. Resource-resource mutualisms most often occur between an autotroph (a photosynthesizing organism) and a heterotroph (an organism which must absorb or ingest food to gain energy). Most plants have a trophic mutualism called a mycorrhizal association, which is a symbiosis between the roots of the plants and a fungus. The fungus colonizes the plants roots and is provided with carbohydrates, sucrose and glucose. In exchange, the plant benefits from the fungi’s higher water and mineral absorption capabilities.

Service-resource mutualisms occur when the symbiotic partner provides a service in exchange for a resource reward. One of the best known examples of this is the exchange between plants and their pollinators. While visiting the plants to gain a supply of energy-rich nectar, the pollinator (insects, birds, moths, bats, etc.), provides the plant with the service benefit of being pollinated, while ensuring their own pollen is distributed when the pollinator visits more plants of the same species.

A rare form of mutualistic symbiosis comes in the form of service-service interactions. As the name suggests, both of the symbiotic partners receive a service, such as shelter or protection from predators. For example, the close relationship between anemone fish (family: Pomacentridae) and sea anemones provides both partners with protection from predators. The anemone fish, which have evolved an extra thick mucus layer on their skin to prevent them from being stung by the anemone’s nematocysts, are provided with shelter from predators and a place to breed, while aggressively chasing away other fish which may try to bite the ends off the nutrient-rich tentacles. However, it is argued that there are very few truly service-service mutualisms as there is usually a resource component to the symbiosis. In the case of the anemone-anemone fish mutualism, the nutrients from the anemone fish waste provide food for the symbiotic algae, which live within the tentacles of the anemone and provide energy to the anemone through photosynthesis. In this way, symbioses are shown to be highly complex and indicative of the delicate balance within ecosystems.

2)      COMMENSALISM

Commensalism is a symbiosis in which one organism benefits from, and is often completely dependent on, the other for food, shelter, or locomotion, with no obvious effect on the host. The relationship between whales and barnacles is an example of commensalism. The barnacles attach themselves to the tough skin of whales, and benefit from widespread movement and exposure to currents, from which they feed, while the whale is seemingly unaffected by their presence. Hermit crabs use the shells of dead snails for homes.

3)      AMENSALISM

On the opposing side of commensalism is amensalism. This occurs when one organism is inhibited or damaged by the presence of the other, who does not benefit. Amensalism may involve competition, in which a larger, more powerful, or environmentally better adapted organism excludes another organism from its food source or shelter; for example, one plant shades out another while growing at its normal speed and height. Alternatively, antibiosis, where one organism secretes chemicals as by-products that kill or damage the other organism, but do not benefit the other, can be seen commonly in nature.

RESERVOIR

In infectious disease ecology and epidemiology, a natural reservoir, also known as a disease reservoir or a reservoir of infection, is the population of organisms or the specific environment in which an infectious pathogen naturally lives and reproduces, or upon which the pathogen primarily depends for its survival. A reservoir is usually a living host of a certain species, such as an animal or a plant, inside of which a pathogen survives, often (though not always) without causing disease for the reservoir itself. By some definitions a reservoir may also be an environment external to an organism, such as a volume of contaminated air or water.

TYPES OF RESERVOIRS

Natural reservoirs can be divided into three main types: human, animal (non-human), and environmental.

Human reservoirs

Human reservoirs are human beings infected by pathogens that exist on or within the human body. Poliomyelitis and smallpox exist exclusively within a human reservoir. Humans can act as reservoirs for sexually transmitted diseases, measles, mumps, streptococcal infection, various respiratory pathogens, and the smallpox virus.

Bushmeat being prepared for cooking in Ghana, 2013. Human consumption of animals as bushmeat in equatorial Africa has caused the transmission of diseases, including Ebola, to people.

Animal reservoirs

Animal (non-human) reservoirs consist of domesticated and wild animals infected by pathogens. For example, the bacterium Vibrio cholerae, which causes cholera in humans, has natural reservoirs in copepods, zooplankton, and shellfish. Parasitic blood-flukes of the genus Schistosoma, responsible for schistosomiasis, spend part of their lives inside freshwater snails before completing their life cycles in vertebrate hosts. Viruses of the taxon Ebolavirus, which causes Ebola virus disease, are thought to have a natural reservoir in bats or other animals exposed to the virus. Other zoonotic diseases that have been transmitted from animals to humans include: rabies, blastomycosis, psittacosis, trichinosis, cat scratch disease, histoplasmosis, coccidiomycosis and Salmonella.

Common animal reservoirs include: bats, rodents, cows, pigs, sheep, swine, rabbits, raccoons, dogs, other mammals.

COMMON ANIMAL RESERVOIRS

Bats

Numerous zoonotic diseases have been traced back to bats. There are a couple theories that serve as possible explanations as to why bats carry so many viruses. One proposed theory is that there exist so many bat-borne illnesses because there exist a large amount of bat species and individuals. The second possibility is that something about bats' physiology make them especially good reservoir hosts. Perhaps bats' "food choices, population structure, ability to fly, seasonal migration and daily movement patterns, torpor and hibernation, life span, and roosting behaviors" are responsible for making them especially suitable reservoir hosts. Lyssaviruses (including the Rabies virus), Henipaviruses, Menangle and Tioman viruses, SARS-CoV-Like Viruses, and Ebola viruses have all been traced back to different species of bats. Fruit bats in particular serve as the reservoir host for Nipah virus (NiV).

Rats

Rats are known to be the reservoir hosts for a number of zoonotic diseases. Norway rats were found to be infested with the lyme disease spirochetes. In Mexico, rats are known carriers of Trypanosoma cruzi, which causes Chagas disease.

Mice

White footed mice (peromyscus leucopus) are one of the most important animal reservoirs for the Lyme disease spirochete (Borrelia burgdorferi). Deer mice serve as reservoir hosts for Sin Nombre virus, which causes Hantavirus Pulmonary Syndrome (HPS).

Monkeys

The Zika virus originated from monkeys in AfricaIn São José do Rio Preto and Belo Horizonte, Brazil the zika virus has been found in dead monkeys. Genome sequencing has revealed the virus to be very similar to the type that infects humans.

ENVIRONMENTAL RESERVOIRS

Environmental reservoirs include living and non-living reservoirs that harbor infectious pathogens outside the bodies of animals. These reservoirs may exist on land (plants and soil), in water, or in the air. Pathogens found in these reservoirs are sometimes free-living. The bacteria Legionella pneumophila, a facultative intracellular parasite which causes Legionnaires' disease, and Vibrio cholerae, which causes cholera, can both exist as free-living parasites in certain water sources as well as in invertebrate animal hosts.

ZOONOSIS

A zoonosis (plural zoonoses, or zoonotic diseases) is an infectious disease caused by bacteria, viruses and parasites that spread between animals (usually vertebrates) and humans.

Major modern diseases such as Ebola virus disease and salmonellosis are zoonoses. HIV was a zoonotic disease transmitted to humans in the early part of the 20th century, though it has now mutated to a separate human-only disease. Most strains of influenza that infect humans are human diseases, although many strains of swine and bird flu are zoonoses; these viruses occasionally recombine with human strains of the flu and can cause pandemics such as the 1918 Spanish flu or the 2009 swine flu. Taenia solium infection is one of the neglected tropical diseases with public health and veterinary concern in endemic regions. Zoonoses can be caused by a range of disease pathogens such as viruses, bacteria, fungi and parasites; of 1,415 pathogens known to infect humans, 61% were zoonotic. Most human diseases originated in animals; however, only diseases that routinely involve animal to human transmission, like rabies, are considered direct zoonosis.

Zoonoses have different modes of transmission. In direct zoonosis the disease is directly transmitted from animals to humans through media such as air (influenza) or through bites and saliva (rabies). In contrast, transmission can also occur via an intermediate species (referred to as a vector), which carry the disease pathogen without getting infected. When humans infect animals, it is called reverse zoonosis or anthroponosis. The term is from Greek: "animal" and "sickness".

DISEASE TRANSMISSION

            A disease reservoir acts as a transmission point between a pathogen and a susceptible host. Transmission can occur directly or indirectly.

1)      DIRECT TRANSMISSION

            Direct transmission can occur from direct contact or direct droplet spread. Direct contact transmission between two people can happen through skin contact, kissing, and sexual contact. Humans serving as disease reservoirs can be symptomatic (showing illness) or asymptomatic (not showing illness), act as disease carriers, and often spread illness unknowingly. Human carriers commonly transmit disease because they do not realize they are infected, and consequently take no special precautions to prevent transmission. Symptomatic persons who are aware of their illness are not as likely to transmit infection because they take precautions to reduce possible transmission of the disease and seek out treatment to prevent the spread of the disease. Direct droplet spread is due to solid particles or liquid droplet suspended in air for some time. Droplet spread is considered the transmission of the pathogen to susceptible host within a meter of distance; they can spread from coughing, sneezing, and talking.

• Neisseria gonorrhoeae (Gonorrhea) is transmitted by sexual contact involving the penis, vagina, mouth, and anus through direct contact transmission.
• Bordetella pertussis (Pertussis) is transmitted by cough from human reservoir to susceptible host through direct droplet spread.

2)      INDIRECT TRANSMISSION

Indirect transmission can occur by airborne transmission, by vehicles (including fomites), and by vectors.

Airborne transmission is different from direct droplet spread as it is defined as disease transmission that takes place over a distance larger than a meter. Pathogens that can be transmitted through airborne sources are carried by particles such as dust or dried residue (referred to as droplet nuclei).

Vehicles such as food, water, blood and fomites can act as passive transmission points between pathogens and susceptible hosts.  Fomites are inanimate objects (doorknobs, medical equipment, etc.) that become contaminated by a reservoir source or someone/something that is a carrier. A vehicle, like a reservoir, may also be a favorable environment for the growth of an infectious agent, as coming into contact with a vehicle leads to its transmission.

Vector transmission occurs most often from insect bites from mosquitoes, flies, fleas, and ticks. There are two sub-categories of vectors: mechanical (an insect transmits the pathogen to a host without the insect itself being affected) and biological (reproduction of the pathogen occurs within the vector before the pathogen is transmitted to a host). To give a few examples, Morbillivirus (measles) is transmitted from an infected human host to a susceptible host as they are transmitted by respiration through airborne transmission. Campylobacter (campylobacteriosis) is a common bacterial infection that is spread from human or non-human reservoirs by vehicles such as contaminated food and water. Plasmodium falciparum (malaria) can be transmitted from an infected mosquito, an animal (non-human) reservoir, to human host by biological vector transmission.

UNIT NO. II EPIDEMIOLOGY OF DISEASES

EPIDEMIOLOGY

            The word epidemiology comes from the Greek words epi, meaning on or upon, demos, meaning people, and logos, meaning the study of. In other words, the word epidemiology has its roots in the study of what befalls a population. Many definitions have been proposed, but the following definition captures the underlying principles and public health spirit of epidemiology:

            Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems.

            Epidemiology is a scientific discipline with sound methods of scientific inquiry at its foundation. Epidemiology is data-driven and relies on a systematic and unbiased approach to the collection, analysis, and interpretation of data. Basic epidemiologic methods tend to rely on careful observation and use of valid comparison groups to assess whether what was observed, such as the number of cases of disease in a particular area during a particular time period or the frequency of an exposure among persons with disease, differs from what might be expected. However, epidemiology also draws on methods from other scientific fields, including biostatistics and informatics, with biologic, economic, social, and behavioural sciences.

            In fact, epidemiology is often described as the basic science of public health, and for good reason. First, epidemiology is a quantitative discipline that relies on a working knowledge of probability, statistics, and sound research methods. Second, epidemiology is a method of causal reasoning based on developing and testing hypotheses grounded in such scientific fields as biology, behavioural sciences, physics, and ergonomics to explain health-related behaviors, states, and events. However, epidemiology is not just a research activity but an integral component of public health, providing the foundation for directing practical and appropriate public health action based on this science and causal reasoning.

DISTRIBUTION

            Epidemiology is concerned with the frequency and pattern of health events in a population:

            Frequency refers not only to the number of health events such as the number of cases of meningitis or diabetes in a population, but also to the relationship of that number to the size of the population. The resulting rate allows epidemiologists to compare disease occurrence across different populations.

            Pattern refers to the occurrence of health-related events by time, place, and person. Time patterns may be annual, seasonal, weekly, daily, hourly, weekday versus weekend, or any other breakdown of time that may influence disease or injury occurrence. Place patterns include geographic variation, urban/rural differences, and location of work sites or schools. Personal characteristics include demographic factors which may be related to risk of illness, injury, or disability such as age, sex, marital status, and socioeconomic status, as well as behaviours and environmental exposures.  Characterizing health events by time, place, and person are activities of descriptive epidemiology, discussed in more detail later in this lesson.

DETERMINANTS

            Epidemiology is also used to search for determinants, which are the causes and other factors that influence the occurrence of disease and other health-related events. Epidemiologists assume that illness does not occur randomly in a population, but happens only when the right accumulation of risk factors or determinants exists in an individual. To search for these determinants, epidemiologists use analytic epidemiology or epidemiologic studies to provide the “Why” and “How” of such events. They assess whether groups with different rates of disease differ in their demographic characteristics, genetic or immunologic make-up, behaviours, environmental exposures, or other so-called potential risk factors. Ideally, the findings provide sufficient evidence to direct prompt and effective public health control and prevention measures.

HEALTH-RELATED STATES OR EVENTS

            Epidemiology was originally focused exclusively on epidemics of communicable diseases but was subsequently expanded to address endemic communicable diseases and non-communicable infectious diseases. By the middle of the 20th Century, additional epidemiologic methods had been developed and applied to chronic diseases, injuries, birth defects, maternal-child health, occupational health, and environmental health. Then epidemiologists began to look at behaviors related to health and well-being, such as amount of exercise and seat belt use. Now, with the recent explosion in molecular methods, epidemiologists can make important strides in examining genetic markers of disease risk. Indeed, the term health-related states or events may be seen as anything that affects the well-being of a population. Nonetheless, many epidemiologists still use the term “disease” as shorthand for the wide range of health-related states and events that are studied.

APPLICATION

            Epidemiology is not just “the study of” health in a population; it also involves applying the knowledge gained by the studies to community-based practice. Like the practice of medicine, the practice of epidemiology is both a science and an art. To make the proper diagnosis and prescribe appropriate treatment for a patient, the clinician combines medical (scientific) knowledge with experience, clinical judgment, and understanding of the patient. Similarly, the epidemiologist uses the scientific methods ofdescriptive and analytic epidemiology as well as experience, epidemiologic judgment, and understanding of local conditions in “diagnosing” the health of a community and proposing appropriate, practical, and acceptable public health interventions to control and prevent disease in the community.

EPIDEMIOLOGY OF TUBERCULOSIS

Tuberculosis or TB, as it’s commonly called is a contagious infection that usually attacks your lungs. It can spread to other parts of your body, like your brain and spine. A type of bacteria called Mycobacterium tuberculosis causes it. In the early 20th century, TB was a leading cause of death in the United States. Today, most cases are cured with antibiotics. But it takes a long time. You have to take meds for at least 6 to 9 months. In the 20^th century, TB was a leading cause of death in the United States. Today, most cases are cured with antibiotics. But it takes a long time. You have to take meds for at least 6 to 9 months.

TUBERCULOSIS TYPES

A TB infection doesn’t mean you’ll get sick. There are two forms of the disease:

1)      Latent TB: You have the germs in your body, but your immune system stops them from spreading. That means you don’t have any symptoms and you’re not contagious. But the infection is still alive in your body and can one day become active. If you’re at high risk for re-activation for instance, you have HIV, your primary infection was in the past 2 years, your chest X-ray is abnormal, or your immune system is compromised your doctor will treat you with antibiotics to lower the risk for developing active TB.  

2)      Active TB: This means the germs multiply and can make you sick. You can spread the disease to others. Ninety percent of adult cases of active TB are from the reactivation of a latent TB infection.

SIGNS AND SYMPTOMS

There aren’t any for latent TB. You’ll need to get a skin or blood test to find out whether you have it. There are usually signs if you have active TB disease. They include: A cough that lasts more than 3 weeks, Chest pain  Coughing up blood, Feeling tired all the time Night sweats  Chills, Fever Loss of appetite, Weight loss  If you have any of these symptoms, see your doctor to get tested. Get medical help right away if you have chest pain.

CAUSES AND HOW TB IS SPREAD

Tuberculosis is caused by bacteria that spread through the air, just like a cold or the flu. When someone who has it coughs, sneezes, talks, laughs, or sings, tiny droplets that contain the germs are released. If you breathe in these germs, you can get it. TB can spread from person to person, but it isn’t easy to catch. You usually have to spend a lot of time around someone who has a lot of bacilli in their lungs. You’re most likely to catch it from co-workers, friends, and family members. Tuberculosis germs don’t thrive on surfaces. You can’t get the disease from shaking hands with someone who has it or by sharing their food or drink. 

DIAGNOSIS

There are two common tests for tuberculosis, but they don’t tell you whether you have latent or active TB:

1)       SKIN TEST

This is also known as the Mantoux tuberculin skin test. A health care worker injects a small amount of fluid into the skin of your lower arm. After 2 or 3 days, they’ll check for swelling in your arm to determine your results. If your results are positive, you probably have been infected with TB bacteria. But the results can be false positive. If you’ve gotten a tuberculosis vaccine called bacillus Calmette-Guerin (BCG), the test could say you have TB when you really don’t. The results can also be false negative, saying that you don’t have TB when you really do, if your infection is recent. You might get this test more than once.

2)       BLOOD TEST

These tests, also called interferon-gamma release assays or IGRAs, measure the response when TB proteins are mixed with a small amount of your blood.

If you have a positive skin or blood test, your doctor will probably give you a chest X-ray or CT scan to look for changes in your lungs. They also might test for TB bacteria in your sputum, the mucus that comes up when you cough. These results will help diagnose latent or active TB.

TREATMENT

Your treatment will depend on whether you have latent TB or active TB. If you have latent TB, your doctor will probably give you medications to kill the bacteria so you don’t develop active TB. If you start to see any of the symptoms of active TB, call your doctor right away. Your doctor will treat active TB with a combination of medications. You’ll take them for 6 to 12 months. Whether you have latent or active TB, it’s important to finish taking all of your medications, even if you feel better after starting them.

RISKS

You can get TB only if you come into contact with others who have it. Other things that could increase your risk include:

1)       A friend, co-worker, or family member has active TB.

2)       You live in or have traveled to an area where TB is common, like Russia, Africa, Eastern Europe, Asia, Latin America, and the Caribbean.

3)       You’re part of a group in which TB is more likely to spread, or you work or live with someone who is. This includes homeless people, people with HIV, people in jail or prison, and people who inject drugs into their veins.

4)       You work or live in a hospital or nursing home.

5)       You’re a health care worker for patients at high risk of TB.

6)       You’re a smoker.

COMPLICATIONS

   A healthy immune system fights the TB bacteria. But if you have any of the following, you might not be able to fend off active TB disease HIV or AIDS, Diabetes, Severe kidney disease, Head and neck cancers, Cancer treatments such as chemotherapy, Low body weight and malnutrition,  Medications for organ transplants, Certain drugs to treat rheumatoid arthritis, Crohn’s disease. Babies and young children also are at greater risk because their immune systems aren’t fully formed.

PREVENTION

Following precautions should be taken to stop the spread of TB

1)       If you have latent TB, take all of your medication so you don’t develop active TB, which is contagious.

2)       If you have active TB, limit your contact with other people at work, school, or home. Cover your mouth when you laugh, sneeze, or cough. Wear a surgical mask when you’re around other people during the first weeks of treatment.

3)       If you’re traveling to a place where TB is common, avoid getting close to or spending a lot of time in crowded places with people who have TB.

4)       Children in countries where TB is common often get the BCG vaccine. It isn’t recommended in the United States. Other vaccines are being developed and tested.

EPIDEMIOLOGY OF TYPHOID

            Typhoid fever is caused by Salmonella typhi, a Gram-negative bacterium. A very similar but often less severe disease is caused by the Salmonella serotype paratyphi A. In most countries in which these diseases have been studied, the ratio of disease caused by S. typhi to that caused by S. paratyphi is about 10:1.

            Typhoid fever remains a global health problem for Salmonella typhi. It is difficult to estimate the real burden of typhoid fever in the world because the clinical picture is confused with many other febrile infections, and the disease is underestimated because of the lack of laboratory resources in most areas in developing countries. As a result, many cases remain under-diagnosed. In both endemic areas and in large outbreaks, most cases of typhoid fever are seen in those aged 3–19 years.

            Humans are the only natural host and reservoir. The infection is transmitted by ingestion of faecally contaminated food or water. The highest incidence occurs where water supplies serving a large population are faecally contaminated. The incubation period is usually 8–14 days, but may range from 3 days up to 2 months. Some 2–5% of infected people become chronic carriers who harbour S. typhi in the gall bladder. Chronic carriers are greatly involved in the spread of the disease. Many mild and atypical infections occur and relapses are common. Patients infected with HIV are at a significantly increased risk of severe disease due to S. typhi and S. paratyphi.

SUSCEPTIBILITY

            Susceptibility is general. Susceptibility is increased in individuals with gastric achlorhydia and HIV positive people. Specific immunity follows recovery from clinical disease and/or active immunization.

PERIOD OF COMMUNICABILITY

            The disease is communicable for as long as the infected person excretes S.typhi in their excreta, usually after the 1st week of illness through convalescence. Approximately 10% of untreated cases will excrete S. typhi for 3 months and between 2-5% of all cases become chronic carriers.

MODE OF TRANSMISSION

            Mode of transmission is person-to-person, usually via the faecal-oral route. Faecally contaminated drinking water is a commonly identified vehicle. S. typhi may also be found in urine and vomitus and, in some situations, these could contaminate food or water. Shellfish grown in sewage-contaminated water are potential vehicles, as are vegetables. Flies can mechanically transfer the organism to food, where the bacteria then multiply to achieve an infective dose.

            The inoculum size and the type of vehicle in which the organisms are ingested greatly influence both the attack rate and the incubation period. In volunteers who ingested 109 and 108 pathogenic S. typhi in 45 ml of skimmed milk, clinical illness appeared in 98% and 89% respectively. Doses of 105 caused typhoid fever in 28% to 55% of volunteers, whereas none of 14 persons who ingested 103 organisms developed clinical illness.

CLINICAL FEATURES

            The clinical presentation of typhoid fever varies from a mild illness with low grade fever, malaise and dry cough to a severe clinical picture with abdominal discomfort, altered mental status and multiple complications.

            Clinical diagnosis is difficult. In the absence of laboratory confirmation, any case of fever of at least 38 °C for 3 or more days is considered suspect if the epidemiological context is suggestive. Depending on the clinical setting and quality of available medical care, some 5–10% of typhoid patients may develop serious complications, the most frequent being intestinal haemorrhage or peritonitis due to intestinal perforation.

            The severity and outcome of the infection is influenced by many factors including; duration of illness before the initiation of treatment, the choice of antimicrobial treatment, age, previous exposure or vaccination history, the virulence of the bacterial strain, the quantity of inoculums ingested, host factors (e.g. AIDS or other causes of immune-suppression) and whether the individual was taking other medications such as H2 blockers or antacids to diminish gastric acid. Patients who are infected with HIV are at significantly increased risk of clinical infection with S. typhi and S. paratyphi.

Acute non-complicated disease

            Acute typhoid fever is characterized by prolonged fever, disturbances of bowel function (constipation in adults, diarrhoea in children), headache, malaise and anorexia. Bronchitic cough is common in the early stage of the illness. During the period of fever, up to 25% of patients show a rash or rose spots, on the chest, abdomen and back.

Complicated disease

            Acute typhoid fever may be severe, with up to 10% of patients developing serious complications. Intestinal perforation has also been reported in up to 3% of hospitalized cases. Abdominal discomfort, the symptoms and signs of intestinal perforation and peritonitis, are other complications. Altered mental status in typhoid patients has been associated with a high case-fatality rate. Such patients generally have delirium and may progress to coma.

            Other rarely reported complications include: Typhoid meningitis, encephalomyelitis, Guillain-Barre syndrome, cranial or peripheral neuritis, and psychotic symptoms. Other serious complications documented with typhoid fever include haemorrhages (causing rapid death in some patients), Hepatitis, myocarditis, pneumonia, disseminated intravascular coagulation, thrombocytopenia and haemolytic uremic syndrome. In the pre-antibiotic era, which had a different clinical picture, if patients did not die with peritonitis or intestinal haemorrhage, 15% of typhoid fever cases died with prolonged persistent fever and diseases for no clear reason. Patients may also experience genitourinary tract manifestations or relapse, and/or a chronic carrier state may develop.

Carrier state

            1-5% of patients, depending on age, become chronic carriers harbouring S.typhi in the gallbladder.

Standard case definitions/classifications of Typhoid fever

Confirmed case	·         A patient with persistent fever (38 °C or more) lasting 3 or more days, with laboratory-confirmed S. typhi organisms (blood, bone marrow, bowel fluid) ·         A clinical compatible case that is laboratory confirmed
Probable case	·         A patient with persistent fever (38 °C or more) lasting 3 or more days, with a positive sero-diagnosis or antigen detection test but no S. typhi isolation ·         A clinical compatible case that is epidemiologically linked to a confirmed case in an outbreak
Chronic Carrier	·         An individual excreting S. typhi in the stool or urine for longer than one year after the onset of acute typhoid fever ·         Short-term carriers also exist, but their epidemiological role is not as important as that of chronic carriers. ·         Some patients excreting S. typhi have no history of typhoid fever

 LABORATORY ANALYSIS

            Blood culture samples and stool/rectal swab have been used to culture for isolation of S typhi. Bone marrow aspirate is a very painful sample to collect though the yield is high. Guidelines for specimen handling for this organism are important for optimal recovery of the bacteria.

Isolates

            Submission of Salmonella isolates to the National Microbiology Reference Laboratory (NMRL) is required by law.

Specimens: Stool for culture.

Collection: Use an enteric kit (bottle with a Cary-Blair medium (0.16% agar))

Amount: Marble size (3-10 gram sample; preferred over rectal swabs)

Call the laboratory for information on other specimen types and correct specimen collection.

Specimen transportation

            For blood culture it is essential to inoculate media at the time of drawing blood. For other specimens it is advisable to make the time of transportation to the laboratory as short as possible. It is more important to process the specimens quickly than to keep them cold. Once they have been inoculated, blood culture bottles should not be kept cold. They should be incubated at 37°C or, in tropical countries, left at room temperature, before being processed in the laboratory.

Blood

            The volume of blood cultured is one of the most important factors in the isolation of S. typhi from typhoid patients: 10-15 ml should be taken from schoolchildren and adults in order to achieve optimal isolation rates; 2-4 ml is required from toddlers and preschool children. Blood should be drawn by means of a sterile technique of venous puncture and should be inoculated immediately into a blood culture bottle with the syringe that has been used for collection.

            In order to assist the interpretation of negative results the volume of blood collected should be carefully recorded. The blood culture bottle should then be transported to the main laboratory at ambient temperature (15°C to 40°C) as indicated above. Blood cultures should not be stored or transported at low temperatures. If the ambient temperature is below15°C it is advisable to transport blood cultures in an incubator. Blood culture bottles should be transported to the referral laboratory at ambient temperature.

Serum

            For serological purposes, 1 to3 ml of blood should be inoculated into a tube without anticoagulant. A second sample, if possible, should be collected at the convalescent stage, at least 5 days later. After clotting has occurred the serum should be separated and stored in aliquots of 200 ml at +4°C. Testing can take place immediately or storage can continue for a week without affecting the antibody titre. The serum should be frozen at -20°C if longer-term storage is required.

Stool

            Stool can be collected from acutely ill patients and they are especially useful for the diagnosis of typhoid carriers. The isolation of S. typhi from stool is suggestive of typhoid fever.  However, the clinical condition of the patient should be considered. Stool specimens should be collected in a sterile wide-mouthed plastic container. The likelihood of obtaining positive results increases with the quantity of stool collected. Specimens should preferably be processed within two hours after collection. If there is a delay, the specimens should be stored in a refrigerator at 4°C or in a cool box with freezer packs, and should be transported to the laboratory in a cool box. Stool culture may increase the yield of culture-positive results by up to 5% in acute typhoid fever. If a stool sample cannot be obtained, rectal swabs inoculated into Carry Blair transport medium can be used but these are less successful.

DIAGNOSIS

WIDAL TEST

            Widal test is used to identify specific antibodies in serum of people with typhoid by using antigen-antibody interactions. In this test, the serum is mixed with a dead bacterial suspension of salmonella having specific antigens on it. If the patient's serum is carrying antibodies against those antigens then they get attached to them forming clumping which indicated the positivity of the test. If clumping does not occur then the test is negative. The Widal test is time-consuming and prone to significant false positive results. The test may also be falsely negative in the early course of illness. However, unlike the Typhidot test, the Widal test quantifies the specimen with titres.

TYPHIDOT

            The test is based on the presence of specific IgM and IgG antibodies to a specific 50Kd OMP antigen. This test is carried out on a cellulose nitrate membrane where a specific S. typhi outer membrane protein is attached as fixed test lines. It separately identifies IgM and IgG antibodies. IgM shows recent infection whereas IgG signifies remote infection. The sample pad of this kit contains colloidal gold-anti-human IgG or gold-anti-human IgM. If the sample contains IgG and IgM antibodies against those antigens then they will react and get turned into red color. This complex will continue to move forward and the IgG and IgM antibodies will get attached to the first test line where IgG and IgM antigens are present giving a pink-purplish colored band. This complex will continue to move further and reach the control line which consists of rabbit anti-mouse antibody which bends the mouse anti-human IgG or IgM antibodies. The main purpose of the control line is to indicate a proper migration and reagent color. The typhidot test becomes positive within 2–3 days of infection. Two colored bands indicate a positive test. Single-band of control line indicates a negative test. Single-band of first fixed line or no bands at all indicates invalid tests. The most important limitation of this test is that it is not quantitative and the result is only positive or negative.

TUBEX TEST

            Tubex test contains two types of particles brown magnetic particles coated with antigen and blue indicator particles coated with O9 antibody. During the test, if antibodies are present in the serum then they will get attached to the brown magnetic particles and settle down at the base and the blue indicator particles remain up in the solution giving a blue color that indicates positivity of the test.

            If the serum does not have an antibody in it then the blue particle gets attached to the brown particles and settled down at the bottom giving no color to the solution which means the test is negative and they do not have typhoid.

Action and alert threshold

The alert threshold for typhoid is 1 case. The action threshold is 5 suspected cases per 50,000 population

CONTROL MEASURES

A) EDUCATION

Educate community members, notably the most vulnerable who include food handlers and people in group settings such as day care/Crèche staff and attendees; closed institutions like boarding schools residential homes for the elderly, orphanages and prisons. These are encouraged to do the following:

1.      Practice hand washing with soap and running water before food preparation and eating, after using the toilet, handling soiled diapers, bed linen, etc., and maintain a high standard of personal hygiene in general.

2.      Maintain rigorous standards of cleanliness in food preparation and handling of food, especially salads and other cold-serve foods.

3.      Make sure to properly refrigerate food where possible.

4.      Report all deaths due to diarrhoeal diseases to health workers.

B) HEALTH EDUCATION MESSAGES FOR COMMUNITIES

1.      Eat foods that have been thoroughly cooked and that are still hot and steaming.

2.      Ensure that cooked food is covered to protect it from flies.

3.      Avoid raw vegetables and fruits that cannot be peeled. Vegetables like lettuce are easily contaminated and are very hard to wash well.

4.      When you eat raw fruit or vegetables that can be peeled, peel them yourself. (Wash your hands with soap first.) Do not eat the peelings.

5.      Avoid foods and beverages from street vendors. It is difficult for food to be kept clean on the street, and many travellers get sick from food bought from street vendors.

6.      Treat all drinking water by bringing it to a rolling boil for 1 minute or using Aqua-tablettes /jik or other household water treatment products before you drink it.

7.      Ask for drinks without ice unless the ice is made from boiled or chlorine treated water.

8.      Avoid flavoured ices and juice because they may have been made with contaminated water.

PROPHYLAXIS

            Immunization is not routinely recommended in Zimbabwe except for travellers to areas where Typhoid is endemic. Two vaccines are currently available: Ty21a (oral vaccine) and ViCPS (parenteral/intra muscular vaccine). Neither the polysaccharide vaccine nor the Ty21a vaccine is licensed for children under 2 years of age. The Ty21a vaccine should not be used in patients receiving antimicrobials. For the single dose parenteral vaccine, efficacy is reached 14-20 days after injection and coverage lasts for about 3 years. The oral vaccine’s efficacy is reached 10 days after the third dose (taken in capsular or liquid form every other day); coverage lasts for 3 years.

            Mass vaccination may be an adjunct for the control of typhoid fever during a sustained, high-incidence epidemic, in displaced settings particularly when access to well-functioning medical services is not possible or in the case of a multidrug-resistant strain. Other issues to be considered include surveillance data on the outbreak, cold chain and EPI capacity. If the involved community cannot be fully vaccinated, children aged 2–19 years should be given priority. Typhoid immunization is not 100% effective, and typhoid fever could still occur.

AVOIDING INFECTION

            Typhoid is spread by contact and ingestion of infected human feces. This can happen through an infected water source or when handling food. The following are some general rules to follow when traveling to help minimize the chance of typhoid infection: Drink bottled water, preferably carbonated. If bottled water cannot be sourced, ensure water is heated on a rolling boil for at least one minute before consuming. Be wary of eating anything that has been handled by someone else. Avoid eating at street food stands, and only eat food that is still hot. Do not have ice in drinks. Avoid raw fruit and vegetables, peel fruit yourself, and do not eat the peel.

UNIT 3

RICKETTSIA AND SPIROCHAETES

Brief account of Rickettsia prowazekii, Borrelia recurrentis and Treponema pallidum

A)  RICKETTSIA

            Small Gram negative bacilli, virus like, obligate intracellular parasites. Di erse group of organism’s. Common feature of Intracellular growth, Transmission by hemagogous (blood sucking) Arthropod vectors (Lice, fleas, tick, mites Rickettsia - causative agent of two groups of diseases Typhus fever – Rickettsia prowazekii Spotted fever - Rickettsia Rickettsii

1)      RICKETTSIA PROWAZEKII

Disease - Epidemic Typhus (louse borne typhus)

Host – Humans, natural vertebrate host, guinea pigs, mice and cotton rats.

Vector – Human body louse – Pediculus, humanus, corporis

Head louse may also transmit the infection but not pubic louse.

Transmission

The lice become infected by Rickettsia patient. Rickettsias multiply in the gut of lice and appear in the feces in 3-5 days. Lice succumb to the infection within 2-4 weeks remaining infective till they die. They can transmit infection after about a week of being infected. Lice may be transfer from person to person. Infection is transmitted When the contaminated louse feces is rubbed through the minute abrasions caused by scratching. Occasionally by aerosols of dried louse feces through inhalation or through conjunctiva.

Incubation period is 5-15 days.

The disease starts with fever and chills. A characteristic rash appears on the trunk, spreading over the limbs but sparing the face, palms and soles.

Symptoms

1.     Severe headache

2.     High fever (above 102.2°F)

3.     Confusion

4.     Stupor and seeming out of touch with reality

5.     Low blood pressure (hypotension)

6.     Eye sensitivity to bright lights

7.     Severe muscle pain

B)               SPIROCHETES

Elongated motile, flexible bacteria twisted spirally along the long axis are termed as spirochetes. They are gram negative. Many are free living saprophytes, while some are obligate parasites. They may be aerobic, unaerobic. Reproduction by transverse fission. Treponemes are relatively short, slender spirochetes with fine spirals and pointed or round ends.

1)   TREPONEMA PALLIDUM

Treponema pallidum causes veneral syphilis. (STD) T. Pallidum is thin, delicate spirochete with tapering ends.

Veneral Syphilis – Sexually transmitted disease. The spirochete enters the body through minute abrasions on the mucosa or skin.

Infectivity – Infectivity of a patient to the sexual partner is maximum during the first two years of the disease, the primary, secondary and early latent stage.

a)      Primary syphilis

The primary lesion in syphilis is the chancre at the site of entry of spirochete. Chancre is genital, other common sites are mouth and nipples. Chancre is a painless relatively avascular, circumscribed, indurated superficially ulcered lesions. It is known as hard Chancre.

Chancre is covered by thick, glairy, exudate, rich in spirochetes. The Chancre heals in about 10-14 days even without treatment leaving a thin scar.

b)     Secondary syphilis

Sets in first 2-3 months after the primary lesion heal. During this interval the patient is asymptomatic. The secondary lesions are due to wide spread multiplications of the spyrochetes and their dissemination through the blood. Roseolar or papular skin rashes Mucus patches in the oropharynx Condylomata at the mucocutaneous junction are the characteristic lesions. Spirochetes are abundant in the lesions and consequently the patient is most infectious during the secondary stage.

c)      Latent syphilis

After the secondary lesions disappear, there is a period known as latent syphilis. In many cases this is followed by natural cure but in other after several years’ manifestation of tertiary syphilis appear. These consist of cardiovascular lesions including aneurysms, chronic granulomata and meningovascular manifestations. Tertiary lesion – Contains few spirochetes and may represent manifestations of delayed hypersensitivity. Late tertiary or quaternary syphilis develops in a few cases presenting with neurological manifestations such as general paralysis.

Prophylaxis

As a transmission is by direct contact it is possible to protect against syphilis by avoiding sexual contact with infected individuals. The use of physical barriers (such as condoms, antiseptics (potassium permagnet) or antibiotics may minimize the risk). The use of prophylytic penicillin carries the danger that it may suppress the primary lesion without elevating the infection so that recommendation and treatment of disease may become more difficult.

Treatment

Penicillin is uniformly effective in syphilis. It is necessary to give an adequate dose and maintain the drug level for a sufficiently long period to establish care.

2)   BORRELIA RECURRENTIS

Borrelia is large, motile retractile spirochetes. Borrelia recurrentis causing relapsing fever. Relapsing fever is an arthropod borne infection Two types of relapsing fever – Louse borne and Tick borne

History

      Relapsing fever has been described since the days of the ancient Greeks. After an outbreak in Edinburgh in the 1840s, relapsing fever was given its name, but the etiology of the disease was not better understood for a decade. Physician David Livingstone is credited with the first account in 1857 of a malady associated with the bite of soft ticks in Angola and Mozambique. In 1873, Otto Obermeier History first described the disease-causing ability and mechanisms of spirochetes, but was unable to reproduce the disease in inoculated test subjects and thereby unable to fulfill Koch's postulates. The disease was not successfully produced in an inoculated subject until 1874. In 1904 and 1905, a series of papers outlined the cause of relapsing fever and its relationship with ticks. Both Joseph Everett Dutton and John Lancelot Todd contracted relapsing fever by performing autopsies while working in the eastern region of the Congo Free State. Dutton died there on February 27, 1905. The cause of tick-borne relapsing fever across central Africa was named Spirillum duttoni. In 1984, it was renamed Borrelia duttoni. The first time relapsing fever was described in North America was in 1915 in Jefferson County, Colorado. Sir William MacArthur suggested that relapsing fever was the cause of the yellow plague, variously called pestis flava, pestis ictericia, buidhe chonaill, or cron chonnaill, which struck early Medieval Britain and Ireland, and of epidemics which struck modern Ireland in the famine. This is consistent with the description of the symptoms suffered by King Maelgwn of Gwynedd as recorded in words attributed to Taliesin and with the "great mortality in Britain" in 548 CE noted in the Annales Cambriae.

1)      Epidemic or louse borne relapsing fever

 Caused by Borrelia recurrentis. It is an exclusive human pathogen being transmitted from person to person through body lice Pediculus humaneous corporis. No extra human reservoir is known.

    2) Endemic or tick borne Relapsing fever

Borrelias causing endemic relapsing fever normally live in their natural hosts, rodents or other mammals on which the vector tick feeds. Human infection is only an accidental event.

1)   EPIDEMIC OR LOUSE BORNE RELAPSING FEVER (RF)

Transmission

The bacteria that cause RF infect body lice when they take a blood meal from an infected person. The bacteria multiply in the gut of the louse, but the infection is not transmitted to new hosts when the louse bites a healthy person. Instead, humans acquire the infection when they scratch their bites and accidentally crush a louse, releasing its infected body fluids onto their skin. The bacteria enter through breaks in the skin, typically caused by scratching the itchy louse bites. After entering into the skin, the bacteria multiply in the person’s blood and they can also be found in the liver, lymph glands, spleen and brain.

Symptoms

a.       Headache

b.      Joint pain

c.       Dry cough

d.      Red or purple spots on skin.

The symptoms continue for three to nine days, While the immune system of the patient makes antibodies that attach to the bacteria and clear them from the blood, and the patient appears to recover. However, not all of the bacteria are destroyed. The numbers of bacteria gradually increase,

Four to seven days after recovering from the first episode of fever, the patient ‘relapses’, i.e. the symptoms begin all over again. Almost all the organs are involved There will be pain in the abdomen and an enlarged liver and spleen, in addition to the other symptoms. Without treatment with special antibiotics, 30% to 70% of cases can die from complications such as pneumonia and infection in the brain, leading to coma (a state of deep unconsciousness) and death.

2)   ENDEMIC OR TICK BORNE RELAPSING FEVER

Transmission

The Borrelia persists in the body of infected ticks throughout their life and is also transmitted transovarially so that the ticks act as reservoirs as well as vectors. The Borrelia invades all parts of the body of the tick and is shed in its saliva and feces. So the infection is transmitted to humans through the bite of ticks or their discharge

Symptoms

1.      Headaches

2.      Muscle pain

3.      Joint pain

4.      Chills

5.      Vomiting

6.      Abdominal pain Headaches

Prophylaxis

Prevention of louse borne relapsing fever consists of prevention of louse infestation along with the use of insecticides whenever necessary. Prevention of tick borne disease is less easy and consists of identification of tick infested places and their avoidance or eradication of the vectors. No vaccine is available.

Treatment

Tetracycline Chloramphenicol, Penicillin, Erythromycin

UNIT 4

INSECTS OF ECONOMIC IMPORTANCE

1)      IDENTIFYING FEATURES AND ECONOMIC IMPORTANCE OF HELICOVERPA (HELIOTHIS) ARMAGIRA

Host: This is a polyphagous pest that feeds on pulses, Bengal gram, soya beans, black gram, pea, cotton, maize, tomato, cotton bolls, sun flower and a variety of vegetables.

Damage: Caterpillars cause a variety of damage to different crops. They feed on leaves and tender shoots and bore into the fruits. In pulses, they bore into the pod to feed on seeds, sometimes half of the body remains outside the pod if the pod is small. Fungus and other diseases follow in the damaged fruits. One larva may feed on several fruits before completing development.

Life cycle: Adult moths are medium sized, with a wing span of 3-4 cm. They are extremely variable in colour from buff to light brownish to grayish-brown, marked with dark grayish irregular lines on the fore wing and a broad blackish band near the outer margin. Hind wing is dull whitish in colour, with outer margin broadly black. Sometimes there is a dark spot in the middle of fore wing. Eggs are spherical, dome-shaped with a flat base, 0.5 mm in diameter, yellowish and turn brownish as the embryo develops. They are laid singly on tender leaves and take 2-4 days for hatching.

Full grown larva may be green, pale yellow, pale brown or grayish but always with a dark stripe on the lateral sides of the body. Body also bears inconspicuous tubercles and scattered small hairs. There are 6 larval instars and the entire larval development takes 20-25 days. Pupation takes place in the soil. Pupal period is 10-15 days. Moths emerge and make their way through the soil.

Distribution: Widely distributed in the tropics, subtropics and warmer temperate areas of the old world, up to Germany and Japan.

Control: The pest can be controlled by spraying 0.02% Malathion, endosulphan, endrin, monocrotophos or carbaryl at 15 day interval commencing flowering stage. Dusting with BHC or carbaryl 10-15% also helps.

Ploughing of the field after harvesting kills and exposes the pupae in soil.

Economic importance: The damage caused by H. armigera is annually estimated, world-wide, to exceed US$2 billion, and the bollworm is listed as an A2 quarantine pest by EPPO. In the Middle East it is a major pest of cotton, tomatoes and other solanaceous crops, legumes like peas and beans, and maize (corn). Attacking cotton, the larvae initially feed on leaves, later boring into flowers and bolls. As bolls are infested while too small to sustain the larvae, they move from boll to boll; the affected bolls fail to develop and the quality of the lint is severely spoilt. Slightly damaged bolls are also damaged due to being invaded by rot microorganisms. In tomatoes, the larvae bore into immature, ripening and ripe fruit, preferring the latter, and cause rot. In maize, larvae bore into stems and can cause serious plant lodging. Infesting the developing cobs, larvae penetrate mainly through the “silk” and feed on the seeds. In all cases, the economic value of the crops, for commercial or for industrial use, is much reduced.

2. IDENTIFYING FEATURES AND ECONOMIC IMPORTANCE OF PYRILLA PERPUSILLA

            Pyrilla perpusilla commonly known as Sugarcane plant hopper is mainly found is Asian  countries like Afghanistan, Bangladesh, Burma, Cambodia, India, Indonesia, Nepal, Pakistan,  South China, Sri Lanka, Thailand, and Vietnam. The original host of P. perpusilla is not known but it has been recorded feeding and reproducing on a wide range of species of Gramineae, Leguminae and Moraceae families.

IDENTIFICATION OF PYRILLA PERPUSILLA

Adult Pyrilla perpusilla is a pale tawny-yellow, soft-bodied insect with head prominently  drawn forward to form a snout. The wingspan of males is 16 - 18 mm and 19 - 21 mm for  females.

LIFECYCLE OR PYRILLA PERPUSILLA

Egg: Females lay eggs on the lower, shady and concealed side of the leaves near the midrib.  Eggs are laid in clusters of 30-40 in number in rows of 4-5. They are covered by pale waxy  material. Eggs are oval-shaped, pale whitish to bluish green when laid and turn brown just  before hatching. A female lays 600 - 800 eggs in her lifetime. First instar nymph has Whitish thorax with a thin transverse pale brown band on the posterior end. Last abdominal segment is green with whitish threads.  Second instar nymph has dark brown strips along the lateral margin

Third instar nymph has a thoracic region with one dark brown dorsal patch on either side.  Abdominal segments are pale blue on dorsal side and pale yellow on ventral side.  Abdominal segments of fourth instar nymph have a dark brown band on the dorsal surface  and pale green ventral surface  Abdominal segments of fifth instar nymph have a dark brown transverse band on the dorsal  surface and pale white ventral surface. Anal tufts are buff colored  Adult: Just after molting, the adults are white colored but later their body turns straw colored,  eyes turn pale green and head develops a snout with a black spot at the posterior side. The  anterior area has numerous minute black spots.  Female measures 10 mm length and 2.2 mm breadth whereas male measures 8 mm length  and 3.5 mm breadth. Adult females are ready to mate 2 days after emergence from the 5th  nymphal instar. Female lays eggs mainly during the day.

DAMAGE CAUSED BY PYRILLA PERPUSILLA

Pyrilla is a major pest in Bihar, Delhi, Haryana, Punjab, Madhya Pradesh, Uttar Pradesh, Maharashtra, Gujrat, and Orissa. In the recent years, its incidence has increased in peninsular India. Leaves turn yellowish white and wither away due to heavy infestation. This infection causes great loss to the yield to poor growth of seed sets and difficulties in milling cane from affected plants.Sucking of sap from the leaves weakens the plant and reduces the sucrose contents by up to 50%. The hoppers exude a sweet sticky fluid called "honeydew” which promotes a quick growth of fungus Capnodium sps. Completely coverage of leaves by the sooty mold affects photosynthesis.

CONTROL MEASURES OF PYRILLA PERPUSILLA

The Burning of trash helps in destroying unhatched eggs and overwintering nymphs. During  pre-monsoon, dusting the fields with HCH 5-10% at 20-30 kg/ha or methyl parathion (2%) at  12.5 kg/ha with a rotary duster can be helpful.

During Pyrilla epidemics aerial sprayings of the following insecticides must be done

*        Fenthion (560 ml/ha), * Malathion (500 ml/ha), * Phosphomidon (250-300 ml/ha)

*        Monocrotophos (1250 ml/ha), * Endosulphan (750 ml/ha)

Economic importance

P. perpusilla is a serious pest of sugarcane in the Orient, but it has also been recorded as a pest of other crops such as rice, wheat, maize and millet. The damage by the pest affects sugar yield and quality (Butani, 1964; Bindra and Brar, 1978; Asre et al., 1983). Losses ranging from 2-34% in sucrose content of the cane and from 3-26% in the purity of the sugar have been recorded. Poor growth of seed sets and difficulties in milling cane from affected plants have also been recorded. However, despite the high economic importance of this pest no review has been published apart from that of Butani (1964).

3. IDENTIFYING FEATURES AND ECONOMIC IMPORTANCE OF PAPILIO DEMOLEUS

Host: This is a common pest of all citrus plants.

Damage: Larvae are voracious feeders of tender leaves and defoliate the trees. They eat leaves from margin inwards, leaving the larger veins intact. Younger plants cannot withstand defoliation and die.

Life cycle: Adult is a large butterfly having a wingspan of 7-8 cm. It has prominent black and yellow markings on the wings. Hind wing has a crimson spot on the tail on dorsal side  and a ring-like eye spot on the anterior margin on the ventral side. They are active fliers  and found throughout the year in plains. Fecundity is 80-150 eggs. Eggs are small, round,  smooth, yellowish and laid singly glued on to the tender leaves. They hatch in 3 -6 days.  First three instars of the larvae resemble bird droppings as they are brownish-black in  colour, with one or two white patches. Last two instars are green in colour, sometimes  with greyish markings, 3-4 cm long and stout anteriorly, with a Y-shaped osmeterium on  the prothorax. They also emit a foul odour when disturbed. Larval period is 8-14 days in  summer but can extend up to 30 days in winter. Pupation takes place on the plant. Pupa,  which is called chrysalis, is 3 cm long, greenish to brown in colour, resembles a twisted  leaf and remains attached to a branch with a fine silken thread. Pupal period is 8-15 days.  The pest completes 5-6 generations in a year and there is no hibernation. Total life cycle  may take 100 days to complete depending on temperature. Peak population occurs in April  and then July to October.

Distribution: The entire Indian subcontinent and SE Asia, China, Japan and Northern  Australia.

Control: Handpicking and destruction of the larvae which are so prominent on the leaves  helps to save the plants in nurseries. Dusting the trees with sodium fluosilicate or BHC 5%  or spraying Malathion, endosulfan, parathion, fentrothion 0.02% or lead arsenate 0.25%  effectively controls the pests orchards. Spraying spores of Bacillus thuringiensis gives  high mortality of caterpillars. The egg-parasites, Trichogramma evanescens, Petromalus  luzonensis and Telenomus sp. destroy large number of eggs. The larval parasites, Erycia  nymphalidaephaga, Charops sp. and Brachymeria sp.have also been recorded on this pest.

Economic importance

The lime butterfly is an economic pest on many cultivated citrus species in India, Pakistan, Iraq, and the Middle East. Due to its history of successful dispersal and range extension, the lime butterfly is likely to spread from its original point of introduction in Hispaniola in the Caribbean to neighboring Florida, Central America, and South America. Due to its capability for rapid population growth under favorable circumstances and its having been recorded to have five generations in a year in temperate regions of China, it is considered a serious potential threat. The caterpillars can completely defoliate young citrus trees (below 2 feet) and devastate citrus nurseries. In mature trees, caterpillars may prefer young leaves and leaf flush. Hand-picking of caterpillars and spraying with endosulfan 35 EC (2 ml/10 litres of water) were the recommended means of pest control by Indian government agencies and agricultural colleges, however, endosulfan has since been banned by the Supreme Court of India.

4. IDENTIFYING FEATURES AND ECONOMIC IMPORTANCE OF CALLOSOBRUCHUS CHINENSIS

Hosts: A pest of pulses, cowpea, soybean, gram, pigeon pea, lablab etc.

Damage: Both larvae and adults cause damage to the grains. They bite holes in the grains  to enter inside and feed on kernel, damaging several grains in the process. As the beetles  can actively fly, the infestation can start in the fields, where the beetles deposit their eggs  on the pods.

Life cycle: Adult beetle is 3-4 mm long, female being larger, brownish in colour, broader  at shoulders and rounded posteriorly. There are dark patches on elytra and thorax. Adults  show sexual dimorphism. Males possess deeply emarginated or indented eyes and  prominently serrate antennae, while in female these characters are not distinctly marked.

In females tip of abdomen is exposed while in males it is covered by elytra. They are active beetles and readily fly when disturbed. Fecundity is about 100 eggs per female.  Eggs are whitish, elongated and stuck on the grains or on pods and sometimes on the surface of the container. Incubation period is 3-6 days. Grubs are scarabeiform or  eruciform, plump and with short legs and yellowish in colour.

First instar larvae bear functional legs and a pair of thoracic plates to facilitate  boring into the seeds. They feed on the inner contents of the grain and may damage several  grains during development. Larval period may vary between 12 and 20 days. Pupation  takes place inside the grain and pupa is dark brown in colour. Occasionally pupation may  take place outside the grain in a cocoon made of excretory matter. Completion of life cycle  takes 4-5 weeks and there may be 6-7 overlapping generations in a year.

Distribution: Cosmopolitan in the tropics and subtropics of the world. A closely related  species, Callosobruchus maculatus is found existing along with chinensis. Adults of the  former species are elongated and darker and posterior part of the abdomen is exposed.

Economic importance: The Adzuki beetle is a major pest of stored lentils. Pod infestation can start in the field before harvest, the pest thus gaining entrance into storage bins. It may cause substantial damage, coming to over 80% losses in weight and in germination rates. Infested seeds are less nutritious and unfit for humans.

5.      IDENTIFYING FEATURES AND ECONOMIC IMPORTANCE OF SITOPHILUS ORYZAE

Rice weevils are usually found in grain storage facilities or processing plants,  infesting wheat, oats, rye, barley, rice, and corn. Although not often found in the home, they  are sometimes found infesting beans, birdseed, sunflower seeds, dried corn, and to a lesser  degree macaroni and spaghetti. Rice weevils do not bite, nor do they damage wood or  furniture.

Identifying features: Adult weevils are about 3/32 to 1/8 inch long (2-3mm). The adult rice  weevil is a dull reddish-brown to black with round or irregularly shaped pits on the thorax  and four light reddish or yellowish spots on the elytra (wing covers). The adult weevil can fly  and is attracted to lights. The larval stage is legless, humpbacked, and white to creamy white,  with a small tan head. The maize weevil is very similar to the rice weevil, but larger.

Life Cycle: The adult female rice weevil lays an average of 4 eggs per day and may live for  four to five months (producing 250-400 eggs). A single generation can be completed in  around 28 days. The eggs hatch in about 3 days. The larvae feed inside the grain kernel for an  average of 18 days. The pupal stage lasts an average of 6 days (5-16 range). The new adult  will remain in the seed for 3 to 4 days while its cuticle hardens and matures.

Economic importance: Both species of Sitophilus are major pests of several cereal crops,  including barley, maize, oats, rye and wheat, as well as peas, cassava and fruits, like apples in  storage. Under humid, unaerated store conditions, half the grain may be destroyed. As the  larvae feed and tunnel within these commodities, their damage is usually not immediately  noticed. However, emergence holes are large and rugged and the beetles may be seen on the  commodities’ surface.

Control: Control of these insects involves inspection and removal of infested food products,  discarding the heavily infested material, repackaging material in new containers, and  vacuuming kitchen cabinets. Products that need to be retained may be placed in the freezer  for several weeks to kill adults and larvae.

Chemical control: A combination of low dosages of vegetable oils and  an organophosphate (pirimiphos-methyl) was highly toxic to immatures and adults of S.  zeamais. These mixtures retained some controlling activity up to 60 days after application.  However, resistance to pesticides has been reported from several regions. Essential  oils applied as fumigants killed up to 100% of the pest population, and edible oils applied by  contact were also very detrimental. Plant powders prepared from the leaves of five plant  species killed over 50% of the exposed beetle adults.

6.IDENTIFYING FEATURES AND ECONOMIC IMPORTANCE OF TRIBOLIUM CASTANEUM

The red flour beetle (Tribolium castaneum) is a species of beetle in the  family Tenebrionidae, the darkling beetles. It is a worldwide pest of stored products,  particularly food grains, and a model organism for ethological and food safety research.

The red flour beetle attacks stored grain and other food products including flour,  cereals, pasta, biscuits, beans, and nuts, causing loss and damage. The United Nations, in a  recent post-harvest compendium, estimated that Tribolium castaneum and Tribolium  confusum, the confused flour beetle, are "the two most common secondary pests of all plant  commodities in store throughout the world."

The red flour beetle is of Indo-Australian origin and less able to survive outdoors than  the closely related species Tribolium confusum. It has, as a consequence, a more southern  distribution, though both species are worldwide in heated environments. The adult is long-  lived, sometimes living more than three years. Although previously regarded as a relatively  sedentary insect, it has been shown in molecular and ecological research to disperse  considerable distances by flight.

Adult

This species closely resembles the confused flour beetle, except with three clubs at the  end of each of its antennae. Female red flour beetles are polyandrous in mating behavior.  Within a single copulation period, a single female will mate with multiple different males.  Female red flour beetles engage in polyandrous mating behavior in order to increase their  fertility assurance. By mating with an increased number of males, female beetles obtain a  greater amount of sperm. Obtaining a greater amount of sperm is especially important since  many sexually active male red flour beetles are non-virgins and may be sperm-depleted. It is  important to note that red flour beetles engage in polyandry to obtain a greater amount of  sperm from males, not to increase the likelihood of finding genetically compatible sperm.

Economic importance

A major pest of stored products, especially in warmer climates. It infests mostly seeds, kernels and other products, usually those that had already been wounded by other pests or damaged during harvest and storage. The affected product becomes contaminated with faeces, and the increased humidity promotes molding. Economic losses consist of reduced weight and product quality, difficulties in baking, reduced marketability of infested products and an accompanying unpleasant smell. Pest presence may cause allergic responses.

Unit 5: POULTRY FARMING

INTRODUCTION

Poultry are domesticated birds kept by humans for their eggs, their meat or their feathers. These birds are most typically members of the superorder Galloanserae (fowl), especially the order Galliformes (which includes chickens, quails, and turkeys). Poultry also includes other birds that are killed for their meat, such as the young of pigeons (known as squabs) but does not include similar wild birds hunted for sport or food and known as game. The word "poultry" comes from the French/Norman word poule, itself derived from the Latin word pullus, which means small animal. The domestication of poultry took place several thousand years ago. This may have originally been as a result of people hatching and rearing young birds from eggs collected from the wild, but later involved keeping the birds permanently in captivity. Domesticated chickens may have been used for cockfighting at first and quail kept for their songs, but soon it was realized how useful it was having a captive-bred source of food. Selective breeding for fast growth, egg-laying ability, conformation, plumage and docility took place over the centuries, and modern breeds often look very different from their wild ancestors. Although some birds are still kept in small flocks in extensive systems, most birds available in the market today are reared in intensive commercial enterprises

POULTRY FARMING

Poultry farming is defined as a term for rearing and keeping of birds such as fowl, duck and hen for egg and meat. Poultry farming has become popular because it is comparatively easy to start and maintain. It gives quick return within one to six month of investments, is easily manageable and requires less space and labour. Poultry birds and their eggs are a rich source of nutrients.

. Poultry farmers mostly choose chickens for poultry farming. Farmers raise more than 50 billion chickens annually as a source of food, both for their meat and for the eggs. Chickens raised for eggs are usually called layers while chickens raised for meat are often called broilers

POULTRY BREEDING

It refers to mating poultry birds for either maintaining or increasing the current flock or for selecting specific individuals for improvement in one or more characteristics (e.g., for size, weight, egg production, meat quality, behavior, plumage, comb type, or a combination of factors).

COMMON BREEDS OF POULTRY BIRDS

Indian poultry breeds provide good quality meat but produces small sized eggs. They have natural immunity against common diseases as compared to exotic varieties bred abroad which require greater protection and immunization.

THE CHICKEN IS COMMONLY CLASSIFIED ON THE BASIS OF ITS ORIGIN

POULTRY HOUSING

Poultry production systems should provide fresh air, clean feed and water, protection against predators, shelter from cold, rain, wind, sun and excessive heat; as well as a source of heat when birds are young. Basically, the birds need to be able to grow, sleep and lay eggs in comfort. The birds should also be free from stress and disease. The basic requirements for poultry housing are

(i)                 Protection from weather

(ii)               Protection from predators

(iii)             Enough space

(iv)             Adequate ventilation

(v)               A clean environment

(vi)             Access to dust bathing facilities

SPACE REQUIREMENTS OR DENSITY OF BIRDS PER UNIT AREA

This is the most important basic principle in housing, as the space available determines the number and type of poultry that can be kept.

MINIMUM SPACE REQUIREMENTS FOR DIFFERENT POULTRY

SYSTEM OF POULTRY HOUSING

I. DEEP LITTER SYSTEM

Birds are fully confined within a house (3 to 4 birds/ m2) but can move around freely. The floor is covered with a deep litter (5 to 10 cm deep layer) of grain husks (maize or rice), straw, wood shavings or a similarly absorbent, non-toxic material. The fully enclosed system protects the birds from thieves and predators and is suitable for specially selected commercial breeds of egg or meat producing poultry (layers, breeder flocks and broilers).

II. SLATTED FLOOR SYSTEMS

Wire or wooden slatted floors are used instead of deep litter, which allow stocking rates to be increased to five birds/m^ of floor space. Birds have reduced contact with faeces and are allowed some freedom of movement. Faeces can be collected from below the slatted floor and used as fertilizer.

III. BATTERY CAGE SYSTEMS

This is usually used for laying birds, which are kept throughout their productive life in small cages. There is a high initial capita investment, and the system is mostly confined to large-scale commercial egg layer operations.

3. BROILER MANAGEMENT OF POULTRY

1.      Since broilers are being reared for meat it is important that they always have an adequate supply of high quality broiler feed.

2.      As the birds get heavier, they will need more floor space and ventilation.

3.      It may be well to use night lights equivalent to 15 watts per 200 square feet. This allows birds to eat at night and helps prevent pile-ups.

4.      Keep litter dry to help prevent breast blisters. Provide ample cool, clean water.

4. PULLET MANAGEMENT OF POULTRY

1.      Feed starter and grower feeds as outlined under Feed and Water section.

2.      Keep young and old birds separated. If it is necessary for one person to care for young and old birds, care for the young birds first each day.

3.      Remove any unthrifty pullets.

4.      Keep birds free of parasites.

5.      Keep complete and accurate records.

5. LAYER MANAGEMENT OF POULTRY

1.      Clean and disinfect laying house before placing pullets in it.

2.      If floor management is used, put in 4 to 6 inches of clean litter.

3.      House only well developed well fleshed pullets.

4.      Use artificial light to provide 14 hours of total light per day – one 40 watt bulb per 200 square feet, hung 8 feet above the floor.

5.      Use a feeding program as outlined above.

6.      Keep birds free of parasites.

7.      Keep complete and accurate records.

8.      Remove obvious culls.

6. BROODING OF POULTRY

The care and management of young chicks during early part of their life is called brooding i.e. up to the age of 3-5 weeks.

BROODERS

1.      Hover-type – Follow manufacturer’s direction. Starting temperature at the edge of the hover should be 95 degrees F. for the first week and reduced 5°F each week.

2.      Heat lamp – Use either white or infra-red heat lamps.

3.      Home made brooder – An inexpensive method of supplying heat to a few chicks is to place a 100-watt light bulb inside a gallon tin can and place the can on the floor of the brooder house.

7. CAGES FOR POULTRY

Normally cages are 18 inches deep and 16 inches high in the following widths

1.      8 inches wide – one bird per cage

2.      10 inches wide – can accommodate two layers per cage.

3.      12 inches wide – can accommodate two or three layers per cage.

4.      Although more than one bird per cage can be housed, one bird per cage is recommended for small flocks for the following reasons; cleaner eggs, fewer cracked eggs, usually higher production, better bird plumage and less cannibalism. Manure management is much easier since the manure is not so concentrated, thus aiding in drying and reducing odors and fly problems.

8. INCUBATION AND HATCHING PROCEDURES OF POULTRY

I. HATCHING EGG PRODUCTION AND CARE

1.      Keep 1 male for each 10-12 females.

2.      Males should be kept with females at least 1 week prior to saving hatching eggs to insure high egg fertility.

3.      Feed a complete diet.

4.      Collect eggs at least 3 limes per day.

5.      The hatching of fertilized eggs requires about 21 days and hatching takes place at 38°C temperature.

II. INCUBATION ESSENTIALS

(a) Obtaining a small incubator

Still air incubator can be purchased or constructed. Small forced-air self-turning incubators are commercially available. For details regarding incubators, incubator parts and/or construction plans, contact an extension poultry specialist or see “Incubation, Embryo Development and Display, and Baby Chick Care”.

(b) Proper operating temperature

A still air incubator requires an operating temperature of 102 to 103°F. At a position level with the top of the eggs. A forced draft (which contains a fan for circulating the air) incubator should be operated at 99 to 100°F. Do not place the incubator in drafts or direct sunlight which may cause extreme fluctuations in temperature.

(c) Sufficient humidity

Wet bulb reading of 86°F. For a small incubator, moisture can be added to the air by placing a small pan of water under the egg tray. It may be necessary to sprinkle the eggs lightly with warm water at the time of hatching to prevent the chicks from sticking to the shell.

(d) Turning of eggs

Eggs should be turned an odd number of times and a minimum of three times each day. Mark each egg as an aid in determining that all eggs are turned from one side to the other at each turning. For self- turning incubation, follow manufacturer’s instructions.

(1) An Egg contains 67% water, 13% protein, 9% fat and 11% minerals.

(2) Moulting

It is a natural physiological process for the birds to renew old feathers at the end of the first year of lying.

(3) Dubbing

Removal of comb may be restricted to in day old chicks belonging to breeds, which have larger/ lopped comb.

(4) Debeaking

Debeaking is cutting off part of the upper beak. It helps in preventing peaking injuries and cannibalism among chicks.

(5) Poultry Disease

Rearing of poultry birds requires properly ventilated place and vaccination of new born chicks. Poultry diseases can be classified as infectious or non-infectious. Non-infectious diseases are caused by faulty management, faulty feed preparation and inadequate diet or nutritionally efficient disease.

A) THE PRINCIPLES OF POULTRY HUSBANDRY

There are a number of requirements by which animals should be managed so that the best performance is achieved in a way acceptable to those responsible for the care of the animals and to the community generally. These requirements are the keys to good management and may be used to test the management of a poultry enterprise in relation to the standard of its management. These requirements are also called Principles. The importance of each Principle changes with the situation and thus the emphasis placed on each may alter from place to place and from time to time. This means that, while the Principles do not change the degree of emphasis and method of application may change. Every facet of the poultry operation should be tested against the relevant principle(s). The Principles of Poultry Husbandry are

1)      THE QUALITY AND CLASS OF STOCK

If the enterprise is to be successful it is necessary to use stock known to be of good quality and of the appropriate genotype for the commodity to be produced in the management situation to be used. The obvious first decision is to choose meat type for meat production and an egg type for egg production. However, having made that decision, it is then necessary to analyse the management situation and market to select a genotype that suits the management situation and/or produces a commodity suitable for that market. A good example is that of brown eggshells. If the market requires eggs to have brown shells, the genotype selected must be a brown shell layer. Another example would be to choose a genotype best suited for use in a tropical environment. The manager must know in detail the requirements of the situation and then select a genotype best suited to that situation.

2)      GOOD HUSBANDRY

The following are of major importance when considering the health, welfare and husbandry requirements for a flock confines the birds. Confining the birds provides a number of advantages

1. Provides a degree of protection from predators
2. Reduces the labour costs in the management of the birds
3. Increases the number of birds that can be maintained by the same labour force
4. Reduces the costs of production
5. Better organization of the stocking program
6. Better organization management to suit the type and age of the birds housed Importantly, the confinement of the birds at higher stocking densities also including a number of disadvantages these are

a.      Increases the risk of infectious disease passing from one bird to another

b.      Increases the probability that undesirable behavioral changes may occur

c.       Increases the probability of a significant drop in performance

d.      Birds housed at very high densities can often attract adverse comments

1)      PROTECTION FROM A HARSH ENVIRONMENT

A harsh environment is defined as the one that is outside of the comfort range of the birds. In this context high and low temperature, high humidity in some circumstances, excessively strong wind, inadequate ventilation and/or air movement and high levels of harmful air pollutants such as ammonia are examples of a harsh environment. Much effort is made in designing and building poultry houses that will permit the regulation of the environment to a significant degree.

It is the responsibility of those in charge, and responsible for, the day-to-day management of the birds that the environment control systems are operated as efficiently as possible. To this end, those responsible require a good knowledge of the different factors that constitute the environment and how they interact with each other to produce the actual conditions in the house and, more importantly, what can be done to improve the house environment.

2)      WELFARE NEEDS

A successful poultry house has to satisfy the welfare needs of the birds which vary with the class, age and housing system. Failure to satisfy these needs will, in many cases, result in lower performance from the birds. These needs include:

a.      The provision of adequate floor space with enough headroom

b.      The provision of good quality food with adequate feeding space

c.       The provision of good quality water with adequate drinking space

d.      The opportunity to associate with flock mates

e.       The elimination of anything that may cause injury

f.       The elimination of all sources of unnecessary harassment

g.      The maintenance of good health

The presence of disease in the poultry flock is reflected by inferior performance. It is essential that the flock is in good health to achieve their performance potential. There are three elements of good health management of a poultry flock. These are:

A.    The prevention of disease

B.     The early recognition of disease

C.     The early treatment of disease

A)    Prevention of disease

Preventing the birds from disease is a much more economical way of health management than waiting for the flock to become diseased before taking appropriate action. There are a number of factors that are significant in disease prevention. These are

1.  Application of a stringent farm quarantine program

a.       The isolation of the farm/sheds from all other poultry.

b.       The control of vehicles and visitors.

c.        The introduction of day-old chicks only onto the farm.

d.       The prevention of access to the sheds by all wild birds and all other animals including vermin.

e.        The provision of shower facilities and clean clothing for staff and visitors.

f.        The control of the movement of staff and equipment around the farm.

2.  The use of good hygiene practices

1. The provision of wash facilities for staff, essential visitors and vehicles prior to entry.
2. The use of disinfectant foot baths at the entry to each shed.
3. The thorough cleaning and disinfection of all sheds between flocks.
4. Maintaining the flock in a good state of well being by good stockmanship, nutrition and housing.
5. The use of a suitable vaccination program.
6. The use of a preventive medication program.
7. The use of monitoring procedures to keep a check on the disease organism status of the farm, to check on the effectiveness of cleaning and sanitation procedures and to test the immunity levels to certain diseases in the stock to check the effectiveness of the vaccination program.

B)    The early recognition of disease

Early recognition of disease is one of the first skills that should be learned by the poultry flock manager. Frequent inspection of the flock to monitor for signs of sickness are required. It is expected that inspection of all the birds is the first task performed each day, to monitor for signs of ill health, injury and harassment. At the same time feeders, drinkers and other equipment can be checked for serviceability. If a problem has developed since the last inspection, appropriate action can be taken in a timely manner.

C)    The early treatment of disease

If a disease should infect a flock, early treatment may mean the difference between a mild outbreak and a more serious one. It is important that the correct treatment be used as soon as possible. This can only be achieved when the correct diagnosis has been made at an early stage. While there are times when appropriate treatment can be recommended as a result of a field diagnosis i.e. a farm autopsy, it is best if all such diagnoses be supported by a laboratory examination to confirm the field diagnosis as well as to ensure that other conditions are not also involved. When treating stock, it is important that the treatment be administered correctly and at the recommended concentration or dose rate. Always read the instructions carefully and follow them. Most treatments should be administered under the guidance of the regular flock veterinarian.

3)      NUTRITION FOR ECONOMIC PERFORMANCE

Diets may be formulated for each class of stock under various conditions of management, environment and production level. The diet specification to be used to obtain economic performance in any given situation will depend on the factors such as:

a.      The cost of the mixed diet

b.      The commodity prices i.e. the income

c.       The availability, price and quality of the different ingredients

Maximizing production is not necessarily the most profitable strategy to use as the additional cost required to provide the diet that will give maximum production may be greater than the value of the increase in production gained. A lower quality diet, while resulting in lower production may bring in greatest profit in the long term because of the significantly lower feed costs. Also the food given to a flock must be appropriate for that class of stock – good quality feed for one class of bird will quite likely be unsuitable for another.

The following are key aspects in relation to the provision of a quality diet:

a.      The ingredients from which the diet is made must be of good quality.

b.      The weighing or measuring of all the ingredients must be accurate.

c.       All of the specified ingredients must be included. If one e.g. a grain is unavailable, the diet should be re-formulated. One ingredient is not usually a substitute for another without re-formulation.

d.      The micro-ingredients such as the amino acids, vitamins, minerals and other similar materials should not be too old and should be stored in cool storage – many such ingredients lose their potency over time, and particularly so at high temperatures.

e.       Do not use mouldy ingredients – these should be discarded. Mould in poultry food may contain toxins that may affect the birds.

f.       Do not use feed that is too old or has become mouldy. Storage facilities such as silos should be cleaned frequently to prevent the accumulation of mouldy material.

4)      THE PRACTICE OF GOOD STOCKPERSONSHIP

The term “stockpersonship” is difficult to define because it often means different things to different people. However, “stockpersonship” may be defined as ‘the harmonious interaction between the stock and the person responsible for their daily care’. There is no doubt that some stock people are able to obtain much better performance than others, under identical conditions. The basis of good stockpersonship is having a positive attitude and knowledge of the needs and behaviour of the stock under different circumstances, of management techniques and a willingness to spend time with the stock to be able to react to any adverse situations as they develop to keep stress to a minimum. Having the right attitude is also a very important element. The stockperson who spends as much time as possible with the stock from day old onward by moving among them, handling them and talking to them, will grow a much quieter bird that reacts less to harassment, is more resistant to disease and performs better.

5)      THE MAXIMUM USE OF MANAGEMENT TECHNIQUES

There are a number of different management techniques available for use by stockpersons that, while not essential for the welfare of the stock, do result in better performance. Examples of these are the regulation of day length, the management of live weight for age and of flock uniformity. The good manager will utilize these techniques whenever possible to maximise production efficiency and hence profitability of the flock.

6)      THE USE OF RECORDS

There are two types of records that need be kept on a poultry enterprise

1)      Those required for financial management – for business and taxation reasons

2)      Those required for the efficient physical management of the enterprise

For records to be of use in the management of the enterprise, they must be complete, current and accurate, be analyzed and then used in the decision making process. Failure to use them means that all of the effort to gather the information will have been wasted and performance not monitored. As a result, many problems that could have been fixed before they cause irreparable harm may not be identified until too late.

7)      MARKETING

There are three important elements to good marketing practice

a.       Produce the commodity required by the consumer – this usually means continuous market research must be carried out to relate production to demand.

b.      Be competitive – higher price is usually associated with good quality and/or specialised product. Therefore, it is necessary to relate price to quality and market demand and to operate in a competitive manner with the opposition.

c.       Reliability – produce a commodity for the market and ensure that supply, price and quality are reliable.

B) MANAGEMENT OF BREEDING STOCK AND BROILER

To attain both genetic potential and consistent flock production, it is important that the producer or flock manager has a good management programme in place. Broiler, also known as Cornish Cross, is a type of chicken raised specifically for meat production. Produced by fast-growing breeds with low mortality, broilers can be reared successfully in standard housing conditions on readily available, custom-formulated broiler federations
Broiler, also known as Cornish Cross, is a type of chicken raised specifically for meat production produced by fast-growing breeds with low mortality, broilers can be reared successfully in standard housing conditions on readily available, custom-formulated broiler feed ratios.

CROSS BREEDS FOR PARENT STOCK (BROILER BREEDERS)

Consumers expect the meat from broilers to be tender and of high quality. The whole broiler production process is designed for this requirement but the same inputs are at odds with those required for egg production by broiler breeders. The three main steps and stages in the whole broiler production process are:

1) rearing and managing broiler breeders
2) fattening of broiler chicks
3) marketing and processing of finished broiler birds

The broiler producer clearly requires birds that will achieve a high body weight, with good carcass quality, over the shortest possible period of time using the minimum amount of regular feed. In addition the producer also wants birds that possess the correct body conformation, which will feather rapidly and have a minimal mortality rate.

On the other hand, producers of broiler breeders (the producer of broiler parent stock) is essentially interested in all factors related to egg production and successful embryo development – onset, frequency and continuity of laying, number, size, weight, shape, and quality of eggs. This is because the producer is focused on producing as many chicks as possible for sale.

But parent birds would have been selected and bred for the fast growing characteristics they pass on to their offspring (i.e. the broiler chicks to be fattened into broilers).  Birds that accumulate weight quickly in the first few weeks after hatching are generally overweight, when mature and egg production is inversely proportional to body weight. Consequently, broiler breeder hens lay only around 140 eggs per year compared with the 250 typically produced by hens laying eggs for human consumption.

A compromise must be built into the breeding programme. Failing this producers of broiler breeders are saddled with the double disadvantage of hens that lay less than 150 eggs per year and are difficult to manage because of rapid growth rate and heavy body weight at maturity.

Compromise is achieved by cross breeding. Simple programmes will typically use a ‘table quality’ strain as the male line (e.g. Cornish) and an egg producing strain (e.g. New Hampshire) for the female line. More complicated schemes yielding a better result would be ‘Cornish’ males and ‘New Hampshire’ females, crossed with the ‘White Plymouth Rock’ strain. Crossbred males and crossbred females from these respective crosses are then used as broiler parent stock to breed the broiler chicks.

High selection pressure for feed efficiency and feed conversion, growth and meat/carcass quality is applied in the male strain, but much less so in the female strain. And the use of crossbred females ensures a high degree of hybrid vigour with maximum levels of egg production, egg viability and hatching success.  

            In slat or deep litter system, keep nest boxes at the rate of one hole for 4 to 5 hens at 18-20 weeks of age. Close the nest holes during night time, to discourage broodiness and soiling of nest material. Introduce males around 22 weeks of age at 8 cocks/ 100 hens or as per the recommendation of the principal breeder. Collect hatching eggs when they reach at least 48-50g weight or from 25 weeks of age whichever is later. Collect eggs at hourly interval during forenoon and once in 2 hours in the after-noon in deep litter and wire floor sheds. In cages collect eggs 2 or 3 times a day. Separate clean, soiled dirty, broken, misshapen and abnormal eggs soon after collection. Save clean eggs with sound shell, shape and size for hatching; without any cleaning. Dry clean soiled eggs with the help of a sand paper, dry cloth or cotton and also save them for hatching. Do not practices wet cleaning of eggs. Discard other eggs which can be sold for table purpose. Fumigate hatching eggs with formaldehyde gas at 3 X concentration and store in an egg store room, until 6 hours before setting. Do not store hatching eggs for more than a week. In case of cage system, rubber mat is placed over the cage floor to prevent hair cracks in hatching eggs. Otherwise, plastic coated steel mesh is used as cage bottom.

C) PROCESSING AND PRESERVATION OF EGGS

There are different methods of processing and preservation of eggs

1. Lime water method

2. Soluble glass method

3. Salicylic Acid and cold storage method

4. Wood ashes or salt method

A) LIME WATER METHOD OF PRESERVING EGGS

Slack four pounds lime, and then add four pounds salt, stirring well together. Add eight gallons water. Stir and leave to settle. The next day stir again. After the mixture has settled the second time draw off or carefully dip out the clear liquid. Take two ounces each of baking soda, cream of tartar, saltpetre, and a little alum. Pulverize and mix, and dissolve in two quarts boiling water. Add this to the lime water. Put the eggs in a stone jar, small end down, one layer on top of another, and pour on the solution. Set the jar away in a cool place. This process has been secret in the past, and the recipe has been widely sold for $5. The method is quite satisfactory, although not so good as the method of preserving in soluble glass, as the eggs are liable to have a somewhat limy taste.

B) SOLUBLE GLASS METHOD OF PRESERVING EGGS

Sodium silicate is a liquid of a rather smooth, slippery consistency, readily soluble in water. For preserving eggs use one quart soluble glass to about 10 quarts pure water. Put the eggs in a stone jar, small end down, one layer on top of another until the jar is filled, then pour on the solution. If the specific gravity of the solution is greater than that of the eggs, as is sometimes the case, add water until the eggs will just sink.

C) SALICYLIC ACID AND COLD STORAGE METHODS OF PRESERVING EGGS

“Submerge the fresh eggs for five or ten minutes in a solution of one ounce of salicylic acid in one quart of strong alcohol, and immediately on removing the eggs from the solution, and while they are still wet, wrap them in sterilized cotton and store in a box or barrel in a dry room, the temperature of which does not go above 60 degrees Fahrenheit.”

D) WOOD ASHES OR SALT FOR PRESERVING EGGS

WOOD ASHES

Experiments conducted by the National Agricultural School in Germany shows that eggs may be kept a year packed in wood ashes, with a loss of only 20 per cent. Wood ashes are cleanly, convenient and always at hand.

SALT

Salt also is good. Use a grade of salt a little coarser than table salt what is called coarse-fine salt. Pack the eggs in a jar. Put in first a layer of salt, then a layer of eggs, and so on until the jar is filled. Stand the eggs upon the small ends, and do not let them touch. Cover them completely with salt. Set the jar in a cool place.

BENEFITS OF POULTRY FARMING BUSINESS

Poultry farming is defined as ‘raising different types of domestic birds commercially for the purpose of meat, eggs and feather production’. Though, the most common and widely raised poultry birds are chicken. Around 5k million chickens are being raised every year as a source of food (both meat and eggs of chicken). The chickens raised for eggs are called as layer chicken, and the chickens which are raised for their meat production are called broiler chickens. Commercial poultry farming is also a very profitable business. It is one of the traditional business ventures. Here we will inform you about the benefits of poultry farming business

Poultry farming business has plenty of benefits. Therefore, many farmers prefer to invest in this business. People generally establish poultry farm for the purpose of producing eggs, meat and generating high revenue from these products. Around, billions of chickens are raised throughout the world as a good source of food from their eggs and meat.

1. Less Capital Required

The main benefit of poultry farming is that it doesn’t require high capital for starting. You just need basic capital to start raising poultry. Also, most of the poultry birds are not expensive to start rising.

2. No Need for a Big Space

Poultry farming doesn’t need a big space unless you are going to start commercially. You can easily raise some birds on your own backyard with one or numerous coops or cages. Hence, if you are interested in poultry farming, then you can simply do it on your own backyard with several birds.

3. High Returns in Short Time Period

Interestingly, commercial poultry farming business ensures high return of investment within a very short time period. Few poultry birds such as broiler chickens take shorter duration of time to mature and generating profit. Poultry products are not much expensive. It can be afforded by most of the people.

4. High Maintenance not required

High maintenance is not required in poultry farm structures. Also, you can minimize diseases and illness in poultry by following proper hygiene and care. Diseases are less in some poultry birds such as quails, turkeys etc.

5. License not Compulsory

It must be noted that, in most cases, you don’t need any license. As almost all types of poultry birds are domestic. Also getting license from the relevant authority is also easy for poultry.

6. Huge Global Demand

Poultry gives you fresh and nutritious food and has a huge global demand. Therefore, global consumers of poultry products prefer them due to their nutrients and freshness.

7. Easy Marketing

Marketing poultry products is very easy. There is an established market for poultry products in almost all places of the world. So you can easily sell the products in your nearest local market.

8. Income & Employment Opportunities

Poultry farming creates income and employment opportunities. Unemployed educated youth can easily make a great income by raising poultry commercially. Women and students can also do this business.

9.Easy Bank Loans

Almost all banks approve loans for these types of business ventures. So, if you want to start this business commercially, then you can apply for loans to your local banks.