Parasitology Lecture Notes PDF

Lecture 1 What is Veterinary Parasitology ? Veterinary Parasitology is the science that deals with the parasites of domestic animals. More specifically, it deals with the interactions between a host and the population of parasites that are found on or in that host. Parasitology is a multidisciplin...

Lecture 1 What is Veterinary Parasitology ? Veterinary Parasitology is the science that deals with the parasites of domestic animals. More specifically, it deals with the interactions between a host and the population of parasites that are found on or in that host. Parasitology is a multidisciplinary para-clinical subject which comprises the field of taxonomy, morphology, biochemistry, physiology, immunology and pharmacology. It is the science that dwells on the anatomy and physiology of parasites, their host(s), transmission, development, impact and their detection and control. Brief history of Parasitology Father of Parasitology: Platter Father of Modern Parasitology: Francesco Redi World 1500 B.C. Ebers Papyrus recorded at least four worm infections in ancient Egypt including Ascaris lumbricoides, Taenia saginata, Dracunculus medinesis (guinea worm) and Schistosoma haematobium. The Bible Description of the disease caused by Dracunculus medinensis, known as guinea worm, was given by the Greeks. Pulling out guinea worms by winding them on a stick was a treatment used. 129-200 Galen recognised Ascaris, Enterobius and Taenia. 1532 Fitzherbert described the liver fluke, Fasciola hepatica 1592 Dunas discovered Diphyllobothrium 1674 Leeuwenhoek described the first coccidian oocysts of Eimeria from rabbit which was later named Eimeria stiedae by Donbell (1922). 1681 Leeuwenhoek first observed Giardia from his own stool 1717 Lancisco suggested that malaria is carried by mosquitoes 1843 Dubini described the hookworm Ancylostoma duodenale 1851 Bilharz described Schistosoma haematobium, Hymenolepis nana and Heterophyes heterophyes 1857 Leuckart and Virchow described independently the life cycle of Trichinella spiralis 1880-81 Thomas and Leuckart described independently the life history of Fasciola hepatica 1 1889 Theobald Smith described Babesia parasites 1893 Theobald Smith and Kilbourne demonstrated the transmission of Babesia by ticks 1898 Ross described the life cycle of avian malaria parasites in mosquitoes 1898 Koch described Theileria parva 1907 Tyzzer described Cryptosporidium 1909 Nicolle and Manceaux discovered Toxoplasma gondii 1910 Chagas first observed Trypanosoma cruzi and its life cycle through bugs 1959-63 Introduction of first commercially produced antiparasite vaccine against Dictyocaulus in sheep and cattle through work of Jarett and co-workers 1972 Rommel; Heydorn and co-workers discovered life cycle of Sarcocystis 1988 Dubey and co-workers discovered Neospora caninum India 1878-79 Lewis reported first mammalian trypanosome, Trypanosoma lewisi in rats 1880 Griffith Evans discovered first pathogenic trypanosome, Trypanosoma evansi from blood of horses and camels suffering from ‘Surra’ 1885 Cunningham discovered Leishmania tropica 1894-99 Alfred Lingard made chemotherapeutic studies against Surra with arsenicals 1897 Ronald Ross found Anopheles mosquito as the vector of human malarial parasite 1898 Ross found Culex fatigans as the vector of bird malaria parasite, Plasmodium relictum 1903 Leishman and Donovan independently discovered Leishmania donovani at Dum Dum in Bengal 1906 Montgomery described blood flukes namely Schistosoma spindale, S. indicum and Orientobilharzia bomfordi of animals 1926 Chandler described Schistosoma incognitum from pig and dog 1932-33 M.A.N. Rao, discovered Schistosoma nasale in the veins of nasal mucosa of cattle 2 1935-36 P.G. Pande described Stephanofilaria assamensis, causing hump sore in cattle 1950 H.N. Ray described Stilbamidine test for diagnosis of latent trypanosomosis in bovines 1958 S.N. Singh described Stephanofilaria zaheeri causing ear sore in buffaloes Parasites The word parasite has been derived from the Greek word Parasitos (Para-beside, sitos- food). Parasite refers to an animal or organism that lives inside or on the body of a different animal called host (another species) and is metabolically dependent on it. In order to survive, the parasites have to overcome several problems some of which include: 1. Host finding and host cell invasion: They must develop successful strategies for finding a suitable finding. They must find methods for attachment and/or for partial or total penetration into their prospective hosts. 2. Metabolism: They must become able to feed on their host’s tissues or fluids and must be able to metabolize the nutrients obtained. 3. Immune Response: They must develop mechanisms to protect themselves from the attacks of the host’s defence systems, e.g., mechanisms for immune evasion. 4. Biotic potential: Parasites have to establish a high reproduction rate in places from which the offspring can be transmitted to other hosts. Types of parasites and their classification: A. According to the duration of parasite on/in the host 1. Temporary parasites: Also known as intermittent or periodic parasites, whose life cycles are not spent entirely on the host and are seen only for certain periods of time. E.g. mosquitoes and bugs. 2. Permanent parasites: Those parasites that spend their entire life cycle within or the host e.g. Melophagus ovinus (sheep ked). B. According to the habitat of the parasite in or on the host 1. Ectoparasite: A parasite that lives on the surface of a host, e.g. Fleas, ticks, lice, flies etc. 2. Endoparasite: A parasite that lives inside the body (body cavity/ organ/ tissue/ cell) of the host, e.g. helminths, protozoan parasites etc. Endoparasites are further of different types: i) Intracellular parasites: Those parasites that live and reproduce inside the host cell, e.g. piroplasms of Babesia bigemina inside RBCs. ii) Intercellular parasites: Those parasites that inhabit spaces in the body of the host. They are also referred as extracellular parasites, e.g. Trypanosoma evansi. 3  iii) Erratic or aberrant or ectopic parasites: Those parasites which are present in locations that are not their usual site, e.g. Fasciola in lungs or brain of sheep. iv) Accidental or incidental parasites: Those parasites found in a host that is not their original host, e.g. Toxocara vitulorum in goats, Dipylidium caninum in children. C. According to the degree of parasitism 1. Obligate parasites: Parasites that cannot complete their life cycle without spending a part of their life cycle on the host, e.g. trematodes. 2. Facultative parasites: Parasites that are not normally parasitic but become parasitic when they accidentally find a host, e.g. Chrysomyia sp. larva in wound. D. According to the type of host required in the life cycle of parasite 1. Monoxenous parasites: Parasites that require only one host to complete its life cycle, e.g. eimerian coccidia etc. 2. Heteroxenous parasites: Parasites that require two or more hosts to complete its life cycle, e.g. Babesia bigemina requiring cattle and ticks. 3. Auto-heteroxenous parasites: Those parasites whose definitive host (vertebrate) at one stage of infection may act as an intermediate host for another susceptible vertebrate host, e.g. Trichinella spiralis. 4. Stenoxenous parasites: Parasites with a narrow host range e.g. Haematopinus suis in pigs, coccidian parasites etc. 5. Euryxenous parasites: Parasites with a wide host range, e.g. Toxoplasma gondii. E. According to size of the parasites 1. Microparasites: Those parasites which can be seen with the aid of a microscope, e.g. Theileria annulata, Hepatozoon canis, Trypanosoma evansi etc. 2. Macroparasites: Those parasites which can be seen with naked eye, e.g. Ascaris suum, Haemonchus contortus etc. F. According to the activity in the day 1. Diurnal parasites: Parasites that are active in the day, e.g. Musca domestica, Tabanus sp. of flies. 2. Nocturnal parasites: Parasites that are active at night, e.g. Anopheline mosquitoes. 3. Crepuscular parasites: Parasites that are active at twilight (dawn or dusk), e.g. the biting midge, Culicoides sp. G. According to transmission to man or animals 1. Zoonotic parasites: Parasites that are transmissible from animals to man and vice versa e.g. Man getting Taenia solium infection after eating under cooked pork. 2. Non zoonotic parasites: Parasites which donot get transmitted from animals to man and vice-versa, e.g. Strongylus vulgaris. 4 H. According to invasion of the tissues of the host 1. Histozoic parasites: Those which lives within the cells and tissues of the host, e.g. coccidia inside the intestinal cells of host. 2. Coelozoic parasites: Those which live in the lumen of the intestine or other hollow organs of the host, e.g. Haemonchus contortus in the abomasum of sheep. I. According to the laying stages by the parasite 1. Oviparous parasites: Those parasites which lay eggs, e.g. Strongylus vulgaris, Ancylostoma sp. 2. Ovo-viviparous parasites: Those parasites which lay eggs containing fully developed larvae to hatch, e.g. Habronema sp. 3. Viviparous parasites: Parasites in which the embryonated eggs hatch in the uterus of the female and larvae are passed out, e.g. Filarid worms. 4. Pupiparous parasites: Those parasites in which the eggs hatch and larvae developed in the uterus and when passed outside they are ready to pupate, e.g. Hippobosca, Melophagus etc. J. According to the specificity of the parasites 1. Host specific parasites: The parasites whose host range is confined to either one species of the host or closely related species of the host, e.g Plasmodium vivax is specific to human beings. 2. Non-host specific parasites: The parasites whose host range is not limited to one species of the host and do not show any marked preference for one species or group of related species of host, e.g. Fasciola, Toxoplasma sp. K. According to development in the host 1. Proliferous parasite: The parasite enters the body of the host as one individual and grows, multiples and eventually produces number of daughter individuals. The daughter individuals further grow and multiply, so do their further progeny, thus the host, who begins with one parasites and finishes with harbouring many, e.g. Theileria, Babesia, etc. 2. Non-proliferous parasites: The parasites enters the body of the host as one individual and grows likewise but the daughter individuals do not multiply in the host in whom they are born. They must get into another host before they can multiply. Thus the host infected with one parasites will never have more than one in his body, e.g. helminths. L. Other parasites 1. Hyperparasites: Those parasites that parasitize other parasites, e.g. Histomonas meleagridis parasitizing the eggs of Heterakis gallinarum. 2. Spurious parasites: These parasites are found transiently in the excretions of the host in view of the host having consumed a parasite of another host, e.g. Eggs of Moniezia in dog faeces after ingestion of Moniezia infected sheep, goat and cattle intestines by the dog. 5 3. Synanthropic parasites: are parasites that are present on human dwellings e.g. houseflies, cockroaches etc. 4. Pseudoparasites: Things that resemble a parasite and which are present in the clinical specimens e.g. plant fibres, yeast, pollen grains etc. 6  Lecture 2 Animal association All animals are in constant interaction with other organisms. These interactions can be divided into two basic types: intra-specific interactions and inter-specific interactions. Intra-specific interactions are those that occur between organisms of the same species, e.g. association between members of a flock of sheep. Inter-specific interactions are those that take place between different species of organism, e.g. association between a sheep and a dog. Generally, an association/ interaction between two organisms living in close physical association is termed as Symbiosis. Any organism that is intimately associated with another organism of a different species is considered to be a symbiont. Symbiosis may be of different kinds viz., mutualism, commensalism, phoresis, parasitism, predation. 1. Mutualism: A kind of association where both partners (symbionts) are mutually dependant on each other. This relationship is usually obligatory and one symbiont cannot survive without the other, e.g., intestinal protozoa in termites, where termites lacking the enzyme cellulase still feeds on cellulose enriched food which is digested by the intestinal protozoa of the termites. 2. Commensalism: An association where one symbiont derives benefit from the other symbiont (host) but the host is neither benefited nor harmed, e.g. Escherichia coli in the intestine of man (host) where it feeds on the unwanted food of the host. 3. Phoresis or phoresy: An association between two symbionts which are merely traveling together and without physiological or biochemical dependence on each other, e.g. bacteria on the legs of a fly. 4. Predation: is the relationship between predators and prey where the predators kill the prey for food. 5. Parasitism: an association in which an organism (parasite) is metabolically dependent on another species of an animal (host). 6. Parasitoids: are those, whose immature stages develop on other parasites and emerge by killing the parasite. E.g. Hymenopteran flies on dipteran flies Types of Parasitism 1) Infestation: Parasitism of host by external parasites e.g. fleas, lice, ticks in livestock. 2) Infection: Parasitism of host by internal parasites, e.g. amphistomes in livestock. Infection can be further of two types: a) Autoinfection: Condition where the juvenile infective form of a parasite, without escaping from the host infects the same host e.g. Cryptosporidium parvum b) Hyperinfection: A condition where the juvenile form of a parasite without exiting the host penetrates in an area adjacent to the site of predilection and establishes in the same host e.g. Strongyloides sp. 3) Congenital (Transuterine or Transplacental): Transmission of parasites from the dam to the foetus across placental membranes, e.g. Toxocara canis in dogs. 4) Transmammary (Transcolostral): Transmission of parasites from the dam to the young one through the milk of the infected dam, e.g. Toxocara cati in cats. 5) Transovarian: Transmission of parasite from the female parent to the progeny through the ova, e.g. Babesia bigemina in ticks. 6) Transtadial: Transmission of parasite from one stage to another stage of the vector, e.g. Theleria annulata in Hyalomma spp. of ticks. Types of host 1. Definitive host or final host: The host in which the parasite reaches maturity and undergoes sexual reproduction, e.g. Sheep for Fasciola hepatica, Dog for Echinoccocus granulosus etc. 2. Intermediate host: The host in which the parasite undergoes its developmental stages (asexually) but cannot develop into an adult or reproduce sexually. Intermediate hosts can be further classified as: a) First intermediate host: The first larval stage of the parasite develops in this host, e.g. snail for Dicrocoelium dendriticum. b) Second intermediate host: This host picks up the early larval stages developed in the first intermediate host. Here these larval stages develop further and reach the infective stages of the parasite, e.g. ants for Dicrocoelium dendriticum. 3. Reservoir hosts: They are vertebrate hosts that harbour a parasite of another host without showing any clinical symptoms, but act a source of infection for the original host, e.g. Game animals for the protozoan parasite Trypanosoma gambiense. 4. Carrier hosts: The vertebrate hosts that have suffered from an infection and in later stage carries the infective organism in its body without showing any clinical signs. 5. Transport hosts: Those that harbour the immature/infective stage of a parasite of another host and help in disseminating the parasite without any development in itself, e.g. earthworms for egg/larvae of Ascaridia galli. 6. Paratenic hosts: Those that harbour the immature/infective stage of a parasite in an encapsulated form and helps in dissemination of the parasite to the definitive host, e.g. Calotes for Spirocerca lupi. 7. Intercalary host: The host that liberates the infective stages of a parasite of another trapped in the body of the original host, e.g. Cats by eating mice liberate the eggs of Capillaria hepatica which are trapped in the liver parenchyma. Vector A vector is an arthropod that carries the parasite between two vertebrate hosts. E.g. Ticks and mosquitoes for various blood protozoans. Vector may be divided into mechanical vector and cyclical vector. 1. Mechanical vector: An arthropod that carries the infectious agent from, one vertebrate host to another without any developmental or biological change in its body, e.g. Tabanus transmitting Trypanosoma evansi by interrupted feeding. 2. Cyclical vector: A vector in which the parasite undergoes development or multiplication before being transmitted to the next host, e.g. Hyalomma anatolicum transmitting Theileria annulata infection. Parasitic Zoonoses These are diseases transmissible between vertebrate animals and man. They can be classified accordingly: 1. On the basis of reservoir host: a) Anthropozoonoses: Infection transmitted to humans from lower vertebrates, e.g., Cystic echinococcosis from animals to humans, Onchocerca volvulus etc. b) Zooanthroponoses: Infection transmitted to lower vertebrate animals from man e.g. Taenia solium from humans to pigs. c) Amphixenoses: Infections shared by both man and lower vertebrates and are transmitted in either direction, e.g. Salmonellosis. 2. On the basis of type of life cycle: a) Direct zoonoses: Infection is transmitted between the two vertebrate hosts through direct contact or a mechanical vector, e.g. Toxoplasmosis, Amoebiosis etc. b) Cyclo-zoonoses: The zoonoses which involves two or more vertebrate hosts (but no invertebrates) for the completion of life cycle, e.g. Echinococcosis, Taeniosis etc. c) Meta-zoonoses: This type of transmission requires an invertebrate host and a vertebrate host, e.g. Schistosomosis, Leishmaniosis etc. d) Saprozoonoses: They include a vertebrate host and an environmental reservoir (food, soil, plant etc.), e.g. Myiasis, Larva migrans etc. Other Terminologies 1. Incubation period: The time lapse between the entry of the parasite and the first appearance or onset of clinical signs. 2. Prepatent Period: The period in which the form of the parasite is demonstrated in the clinical material of the host. 3. Hypobiosis: Temporary cessation in the development of immature stages of some nematode parasites in the host due to adverse environmental conditions, e.g. Ostertagia ostertagi in cattle. The epidemiological importance of hypobiosis is that the resumption of development of hypobiotic larvae usually occurs when conditions are optimal for free‐living development and so results in increased contamination of the environment. 4. Diapause: This phenomenon is observed in arthropods where they survive adverse conditions by cessation of growth and metabolism at a particular stage. It is most common in temporary arthropod parasites in temperate climates. In these, feeding activity is restricted to the warmer months of the year and winter survival is often accomplished by a period of diapause, e.g. Hydrotoea irritans, Stomoxys calcitrans etc. 5. Parthenogenesis (Virgin birth): refers to formation of progeny without fertilization, e.g. Haemaphysalis ticks and Strongyloides sp. of nematodes. 6. Paedogenesis (Juvenile multiplication): Multiplication of juvenile/immature stages of parasite in intermediate host, e.g. Multiplication of immature stages of trematodes in snail. 7. Metagenesis (Alternation of generation): Sexual multiplication alternating with asexual multiplication, e.g. In trematodes where sexual multiplication in definitive host alternates with paedogenesis in intermediate hosts.  Lecture-3 Standardized Nomenclature Of Animal Parasitic Diseases (SNOAPAD) The standard and uniform nomenclature formulated by the World Association for Advancement of Veterinary Parasitology (WAAVP) is Standardized Nomenclature of Animal Parasitic Diseases (SNOAPAD). Nomenclature is the process of naming the parasites. Members belonging to the animal kingdom are classified into phyla, classes, orders, families, genus and species. Later, additional categories such as super or sub were created to accommodate the increasing number of species discovered over the years. Super/Sub was prefixed to the existing categories (Superfamily/ Suborder). The family group includes taxa ranked as at the family and tribe levels (including super and subfamilies). The genus group includes taxa below subtribe and above species. The species group includes taxa ranked as species or subspecies. The names of parasites must be from Latin or Greek and not in the local language. The genus name should be a noun and the species names should be either noun or adjective. The name of the order ends in ‘ida’, e.g. Strongylida, superfamily ends in ‘oidea’, e.g. Ancylostomatoidea, family ends in ‘idae', e.g. Ancylostomatidae and subfamily ends in ‘inae’, e.g. Ancylostominae. The first letter of the genus should always be in capital letter while the first letter of the species should be in small letter except for those whose names have been derived from persons, where, it shall be either in small letter or in capital letter, e.g., Trypanosoma evansi or Trypanosoma Evansi, Cotugnia bhaleraoi or Cotugnia Bhaleraoi. In printed formats, the names of the genus and species should be italicized while in written text, the names of the genus and species should be underlined. The genus and species are also named after morphological characteristics, host, anatomical location, geographical location, scientists etc. The law of giving importance to the scientist who first named the parasite is known as Law of Priority. If the genus and species names are after scientists, the name of the scientists and the year should follow the scientific name. While writing, a comma should be used after the scientists and not anywhere, e.g. Schistosoma nasale, Rao, 1932. If the name of the original author is changed subsequently for valid reasons, his name and the year have to be written within brackets after the new classified name for e.g. Ancylostoma caninum (Ercolani, 1859) Hall, 1913. If a parasite name is changed subsequently for valid reasons, the earlier name is considered as the synonym e.g. Neoascaris vitulorum is the synonym for Toxocara vitulorum. Recommendations of SNOAPAD include The practice of using the suffix ‘osis’ to denote parasitic disease with apparent clinical signs and the suffix ‘iasis’ for subclinical infections are to be discontinued.  The suffix ‘osis’ should be added to the full generic name or the stem of an appropriate higher taxon name or from the genitive name of the parasite by deleting the last one or two letters. In some, the suffix ‘osis’ is added to the full generic name of the parasite, eg., Hepatozoon - Hepatozoonosis, Leucocytozoon - Leucocytozoonosis For certain parasites, the ‘osis’ is added to the appropriate higher taxon name as in the case of Schistosoma eg. Schistosom+osis = Schistosomosis, Ancylostoma - Ancylostom+osis = Ancylostomosis, Babesia - Babesi+osis = Babesiosis When the taxa, ends in ‘x’ as in Demodex, the stem is formed from the genitive as in the given example Demodex, Demodicis - Demodic+osis=Demodicosis Use of nomenclature such as Malaria, Surra, Myiasis, Mange etc., to be continued in addition to the new names as these are well established names and have been in use for a long period.  Lecture 4 Host-parasite relationship Host parasite relationship as the term implies is the relationship between two organisms namely the host and the parasite where the parasites invariably succeed in forging a relationship to its advantage. Parasites upon entering their hosts through various routes may survive or die in the host. If parasites survive they develop and multiply causing infection or disease in the host. In evolution, there is always a tendency towards mutual adjustment between two organisms and therefore both parasite and the host forge a relationship that may either limit the infection so that parasite control is achieved without any pathological changes. Therefore, successful parasites tend to become harmless to the host. Majority of the parasites that survive in their hosts do not endanger their hosts, since they do not want to lose their shelter and food. However, the host tries to expel or kill the parasite by immune responses. When the host attempts to kill the parasite by immune mediated mechanisms, immunopathological lesions develop leading to disease in the animal. Host-Parasite relationship is a dynamic process where the host employs innate and acquired immune mechanisms to destroy the parasite. The nutrition status of the host and the energy resources of the host, at the start of an infection play a role in determining the ultimate outcome of the host parasite relationship. Malnutrition will impede the animal's ability to respond immunologically to the parasite. As parasites are large and complex, the host finds it difficult to counter the parasites by immune mediated mechanisms, resulting in responses that are not always protective. In addition, parasites also evade the immune responses of the host by various ways to ensure their survival and propagation. Therefore, host parasite relationship is an intricate relationship where the host attempts to destroy the parasite but the parasite does not endanger their host lest that they so lose their shelter and food. Host parasite relationship occurs in a complex ecological setting where in vivo and external environments change continuously. Mode of transmission of the parasites Parasites have distinct routes of entering a host. Endoparasites enter the hosts in general through natural openings on the exterior of the body or through the skin. Parasites are transmitted from one animal to another by following routes: 1. Ingestion: The most common mode of transmission of parasites is through ingestion. The host may become infected by direct ingestion of an infective stage through  contamination of food and water or by ingestion of an intermediate host or transport host containing infective stages. Examples, the infective stages of the parasites with direct life cycle like Ascaris suum, Entamoeba histolytica find their way into the feed and water of the host thereby gaining access to the host or the infective stages (third larval stage) may climb up the vegetations and wait for the host to ingest. For parasites with indirect life cycle, the host becomes infected by ingestion of an intermediate host or transport host containing infective stages, e.g. Diphyllobothrium latum, Taenia solium etc. 2. Skin penetration: The infective stages of the parasite may actively penetrate the skin, e.g. cercariae in schistosomes, infective larvae of hookworms. Certain parasites enter the hosts via the bite of an intermediate host serving as a vector, e.g. Sporozoites of Babesia bigemina entering inside blood circulation of cattle by the bite of tick vector Rhipicephalus (Boophilus) microplus. 3. Contact and Predation: Parasites are transmitted between animals by contact especially when they are confined in sheds or houses. Eg. Lice infestation and mange is chiefly transmitted between animals by contact. Parasites are also transmitted during predation by a host. For example, when cats predate on rats, cats may acquire an infection with parasites. 4. Entry through nostrils: Oestrus ovis, the nasal bot fly, deposit its young larvae around the nostrils of the host, where upon they crawl upward and enter the nasal sinuses. 5. Coitus: Tritrichomonas foetus, the protozoan parasite that causes abortion in cattle and Trypanosoma equiperdum, the protozoa that causes dourine in horses are transmitted during coitus. 6. Transplacental/Transmammary transmission: Transplacental or prenatal infection refers to transmission from mother to foetus across the placenta as in Toxocara canis and transcolostral or transmammary transmission refers to transmission from infected dams to nursing offspring via colostrum or milk as in Toxocara vitulorum or Toxocara cati. Methods of dissemination of infective stages of parasites Once parasites are outside the hosts, they have to survive in the environment until they find a suitable host. As the environmental conditions are generally adverse to their survival, the infective stages of parasites are endowed with resilience. These resistant stages have the capability to survive the adverse conditions and remain infective to find a host. Temperature and moisture are two important factors that facilitate or deter parasite survival and development. Parasites generally do not develop below 10oC or above 40oC. When climatic conditions are hostile (freezing temperatures), parasites cease development in hosts (arrested development) and wait for the conditions to improve before they resume development and discharge their eggs in faeces. Dispersal of parasites  1. Water: Important agent for dissemination of parasites. Example includes larvae of Dracunculus which require water bodies for gaining access to cyclops. Parasites that require aquatic habitats for developments such as mosquitoes and black flies are carried to long distances by streams and rivers. Human interventions such as use of sewage and sludge to fertilize pasture, construction of irrigation canals directly facilitate breeding of snails’ thereby aiding dissemination of trematode parasites besides aiding breeding of insects. 2. Fomites: Insects mechanically disseminate the parasites from one place to another. The fungus Pilobolus aids in the dispersal of the lungworm infective larvae from faecal pats to the pasture thereby facilitating infection of cattle hosts. Parasite induced host behavioural changes 1. Metacercariae of Dicrocoelium enters the brain of ants and paralyse them thereby aiding dissemination of parasite infected ants for herbivores during grazing. 2. Grasshoppers infected with tetramers and beetles infected with cysticercoids of tapeworms become sluggish thereby facilitating ingestion of definitive hosts. 3. Ruminants heavily infected with hydatid cysts become debilitated, making them easier prey for carnivores. Strategies adopted by parasites to infect hosts 1. Some parasites employ certain strategies to augment their chances of finding a host. Liver fluke encysts on green parts of plants and on higher parts of the plants to facilitate ingestion by herbivore hosts. 2. As cattle are reluctant to feed on herbages near faeces, the motile gravid segments of Taenia saginata leave the faeces to contaminate the herbage and increase its chances of being eaten by an herbivore as against the non-motile gravid segments of Taenia solium which does not have to leave the faeces because pigs being coprophagic consume the faeces and pick up the infection. 3. Some parasites are endowed with sensory organs to locate hosts. Warmth, CO2, fatty acids, amines etc., serve as stimuli for parasites especially arthropods to locate hosts.  Lecture-5 Parasite specificity in relation to species, breed, sex and location Parasite specificity or Host Specificity is the natural adaptability of a species or groups of parasite to certain species or groups of host and is dependent upon the compatibility of a host to a parasite. In natural host parasite relationships, the parasite must be precisely adapted to the structural and physiological conditions that characterize the host species. This adaptation, which develops over long periods of evolutionary change, is the basis for the phenomenon of host specificity or parasite specificity. Parasite specificity is usually defined in terms or establishment or failure to establish in a host. However, a range of parameters, such as establishment, number, size, developmental stage of worms, duration, level of egg production and duration of infection can give indication of the degree of adaptation to a particular host. For example, the eggs of the human ascarid, Ascaris lumbricoides can hatch in a variety of mammalian hosts but can develop into adults in humans alone. However, in some cases, the restriction is absolute or total as occurring in Eimeria species or the restriction may be very loose and parasite can undergo development in and be transmitted between, a wide variety of hosts like protozoan parasite Toxoplasma gondii. Factors influencing parasite specificity Parasite specificity is also governed by anatomical, physiological and nutritional, beside ecological factors.The anatomy of the host animal may prevent the establishment of a parasite. The intestinal villi or crypts may be too short or intestinal movements too rapid to prevent the establishment of a parasite. Physiological factors such as composition of the bile, dissolved carbon dioxide in hosts, pO2, redox potential and the normal temperature of a host may also regulate host specificity. In unnatural hosts, the unsuitable body temperature may fail to provide the right stimulus for the parasite to establish in hosts. Parasite specificity in relation to host species 1. Host animals are susceptible to some parasites and resistant to others. For example, majority of the helminths of cattle are incapable of infecting sheep and goats. Th normal resistance of various species of animals to various pathogens is due to the presence of antibodies on their erythrocytes called isohaemagglutinins. 2. Many parasites do not develop in hosts other than their natural hosts, e.g Eimeria sp. 3. The red worms (Strongylus sp) of horses are specific to equine hosts and cannot infect cattle, buffalo, sheep and goat. 4. The nematode Ancylostoma caninum is a parasite of both dogs and cats. However, the strain adapted to dog survives better and produces more eggs in dog, as compared to the strain found in cat. Similarly, the cat adapted strain develops better and produces more eggs in the cat as compared to dogs.  5. Limited degree of development of parasite occurs in unnatural host in some cases as in the case of larvae of Ostertagia ostertagi (cattle parasite) in sheep where only few reach to adult stage or the dog parasite, Toxocara canis which undergoes limited development in children causing the condition visceral larval migrans. Parasite specificity in relation to sex 1. Some parasites affect only the females and not the males as in the case of the trematode, Prosthogonimus species which is mostly found in the oviduct of female gallinaceous birds. The influence of sex on helminth burden appears to be largely hormonal. 2. In animals whose oestrus cycle is seasonal, parasites tend to synchronize their development with that of the host. For example, ewes show a spring rise in faecal egg counts after lambing and onset of lactation. 3. In case of female dogs (bitch) above six months old, development of Toxocara canis is influenced by hormonal changes. When they become pregnant, the dormant larvae are activated and transported to the foetus and so puppies are born with Toxocara canis infection. However in the case of male dogs older than 6 months, dormant larvae are not activated but become calcified. Therefore, older male dogs serve as dead end hosts for Toxocara canis. Parasite specificity in relation to breeds 1. Different parasites have varied susceptibility to different breeds. 2. Indigenous breeds of cattle suffer less from tick infestation and tick borne diseases in comparison to cross breds and exotic breeds. 3. N’Dama breed of cattle in Africa and their crosses are tolerant to trypanosomes. Parasite specificity in relation to location in hosts 1. Each parasite has a specific predilection site or a location in hosts. The best example for site specificity is Eimeria species which parasitize only certain areas of the intestine. 2. Other examples include the nematode Dictyocaulus species which affect only the lungs in ruminants and the trematode, Paragonimus species in lungs of dogs. Parasite specificity in relation to locality 1. When parasites are limited to certain ecological or geographical areas as in the case of African animal trypanosomes and human trypanosomes that are restricted to Western, Central and Eastern Africa, it is referred to as ecological or geographical restriction. Tissue reactions caused by parasites to the host 1. Injuries during entry of parasites: Certain parasites cause direct injuries to the host, during the process of entering the host. The hookworms (Anclystoma sp., Bunostomum sp.) cause injuries to the cells and underlying connective tissue when they penetrate the skin of the host. Cercaria of certain schistosomes causes dermatitis while penetrating the host’s skin. 2. Blood loss and anemia: Some parasites suck blood (hookworms, barbers pole worm, mosquitoes, tick etc) from the hosts resulting in anaemia. Haemonchus contortus, in large numbers may bleed the animals causing severe anaemia and mortality in lambs. Heavy infestations with ticks can lead to severe anaemia in animals. 3. Changes in protein metabolism and mineral levels: It commonly occur in parasitic infections especially in helminthic infections. Reduced level of aminoacid incorporation in muscle protein results in reduced weight gain and weight loss. Mineral deficiences affects the growth rates since skeletal size (bone size) ultimately determines the capacity of growing animal to accumulate muscle. All these results in reduced weight gain, reduced wool growth and reduced milk production in infected animals. 4. Destruction of tissues: Many parasites during their course of development undergo migration in the tissues of hosts, e.g., immature stages of liver flukes that migrate in the liver of cattle, sheep and goats causing traumatic hepatitis. Larvae of Toxocara canis, T. cati, T. vitulorum and Ascaris suum migrate through liver and lungs inflicting physical damage, especially to lungs. 5. Injuries during establishment and feeding: Flukes, tapeworms and acanthocephalans armed with suckers, hooks and spines cause irritation to the mucosal surfaces of intestines. Immature stages of amphistomes ingest plugs of mucosal tissues as they feed.Ticks also cause inflammation and leakage of serum from damaged skin in sensitized animals. 6. Mechanical interference: Interference can occur either due to occlusion or pressure atrophy by the parasite. a) Occlusion: Death due to intestinal obstruction by parasites is common, eg. ascarids and tapeworms. Occlusions of bile ducts by liver flukes obstruct the flow of bile resulting in icteri. Gapeworms block the air passages causing dyspnoea and asphyxia in fowls. b) Pressure atropy: Pressure upon organs by larval stages of parasites, especially those of tapeworms result in atropy or distortion of the organ involved. Coenurus cerebralis, the larval stage of the tapeworm Taenia multiceps exert pressure on the brain of sheep causing the condition known as Gid or Staggers. 7. Pathological changes: One of the effects of parasites on hosts includes changes in tissues that are affected by the parasite.Some parasites cause chronic inflammatory reactions resulting in fibrosis and formation of nodules in the inflamed tissues. In Ascaris suum infections, spots of white fibrous tissue (Milkspots) are formed in the liver of affected piglets. Larvae of warble flies form cysts in the back of cattle and develop within it until ready to leave the hosts for pupation on the ground.  Lecture 6 Immunity against parasitic infections or infestations 1. Innate or natural immunity: Immunity possessed by the host animal from birth. In other words, innate immunity is physiological incompatibility between certain parasites and the host that prevents the entry and establishment of the parasite in the host. It is an inherited non-specific immunity and the first line of defense. It constitutes of physical and chemical barrier to infectious agents, identification and removal of foreign substances present in the host body by leucocytes like natural killer cells, mast cells, basophils, eosinophils, macrophages, neutrophils; activation of the complement cascade, production of cytokines etc. Eg. Helminths such as hookworms and schistosomes may not be able to penetrate the skin and gain entry into the host, Trypanosomes upon reaching the blood stream may be destroyed by substances present in serum. Innate immunity can be complete / absolute or incomplete / relative.  A host is said to possess complete innate immunity when a parasite is not able to infect a host under any circumstance, eg. sheep cannot be infected with ascarids.  When a host innately resistant to a species of parasite becomes infected owing to lowered health, it is incomplete innate immunity. 2. Acquired immunity: Immunity acquired by the host during its life time as a result of exposure to a particular parasite or through inoculation of parasite antigen. Acquired immunity may be either active or passive.  Active immunity: is acquired in response to the introduction of live or killed parasites. This may be either natural or artificial. Natural active immunity is derived following repeated exposure to an infection while artificial active immunity is derived by inoculation of parasites or their stages. It is stronger, long lasting, and diverse and takes time to fully develop.  Passive immunity: refers to transfer of antibodies or lymphocytes from immune to non-immune animals. It is only temporary and does not last long. It could be either natural or artificial. Natural passive immunity refers to transfer of immunity naturally from mother to offspring by placenta or through colostrum and these antibodies protect the young for a certain period. Artificial passive immunity is immunity transferred to a non-immune animal through injections of sera produced in another animal by repeated injections of particular antigens. Types of Natural Resistance Different types of natural resistance or immunity viz., premunity, concomitant immunity and sterile/ solid immunity are seen in parasitic infections.  1. Premunity: Immunity that is established after the primary infection has become chronic and is effective only if the parasite persists in the host or in other words premunity is immunity developed due to presence of residual parasites in the host. It is also known as incomplete immunity or infection immunity (Co-infectious immunity). Premunity is commonly associated with haemoprotozoan diseases such as theileriosis and babesiosis. 2. Concomitant immunity: It is one type of premunity developed as a result of stimulation of the host’s immune system by existing adult parasites. This immunity does not interfere with the survival of existing adult parasites but prevents the entry and establishment of newly invading larvae. This type of immunity is seen in schistosomiosis and cystic echinococcosis (hydatidosis). 3. Sterile immunity: Also known as complete immunity, it is maintained by the host even after the parasite is eliminated. The immune system remains sensitized for many years e.g. Cutaneous leishmaniosis (Oriental sore) in man, Theileria annulata infection in cattle, Plasmodium cynomolgi infection in monkeys, etc. Types of immune response in parasitic diseases If the parasite successively overcomes the animal's innate defence mechanisms, it will elicit an immune response specific to the parasite and these immune responses may be humoral mediated or cell mediated. Humoral Immune Response Humoral immunity is mediated through antibodies which are large glycoproteins released by B cells. These antibodies are present in blood, lymph and cerebrospinal fluid. There are five classes of antibodies, each of which is distinguished from the other by their heavy chains. o Immunoglobulin G (IgG): Major antibody in serum. Long half life o Immunoglobulin M (IgM): Largest and the first antibody to be produced in an immune response. Presence denotes acute infection. These antibodies are able to neutralize, fix complement, agglutinate and immobilize parasitic antigens. o Immunoglobulin A (IgA) : Predominantly found in secretions (mucous, saliva, tears) and colostrums and hence called secretory Ab. It is also known as mucosal antibody. o Immunoglobulin E (IgE): Also called as reaginic antibody. This Ab binds to the surface of mast cells and causes degranulation of the cell and release of histamine into circulation. This Ab is associated with helminthic infections or allergies. o Immunoglobulin D (IgD): The function of this Ab with respect to parasitic infections is not known.  Parasites are not composed of a single antigen but a mosaic of antigens. Animal hosts therefore will recognize a number of these different antigens resulting in a polyclonal antibody response. In addition, the host will produce different immunoglobulin classes having the same antigen specificity.   In general, humoral immune response (antibodies) controls extracellular parasites in the intestine, blood stream and tissue fluids. Humoral immune response is predominant in helminthic infections involving IgE, IgA and IgG antibodies. Many helminth infections are associated with characteristic type I hypersensitivity, including eosinophilia, oedema, asthma and urticarial dermatitis where IgE levels and eosinophil levels are increased. One of the major tasks of eosinophils is the destruction of helminths. Cell Mediated Immune Response Cellular immunity is mediated by T cells subsets and their cytokines and like the antibody response; there is involvement of macrophages and the presentation of antigens in combination with specific macrophage surface molecules to the T cells. Specific cytotoxic cells can directly kill parasite infected cells. Some parasites preferentially stimulate T helper cells (subsets Th-1 or Th-2) and each helper T cell subset secretes a characteristic set of cytokines, referred to as a T cell cytokine profile. For example, in Leishmania infections, there will be Th-1 response with a characteristic cytokine profile of interleukins (IL2, IL3, IL-12 and Interferon). Cellular immunity is often directed against intracellular parasites (e.g. Theileria, Toxoplasma etc). Hypersensitivity reactions During the process of destruction and removal of parasites by the host immune system, surrounding body tissues may be damaged. These harmful effects are called as hypersensitivity reaction. The different types of hypersensitivity include:- 1. Type –I (Anaphylactic shock): acute or immediate reaction due to binding of antigen with IgE fixed to mast cells and basophils leading to release of vasoactive, amines (histamine & serotonin) e.g., anaphylactic shock following rupture of hydatid cyst and release of hydatid fluid into the system. 2. Type-II (Cytotoxic): it is a subacute reaction where antigen binds on IgG or IgM antibody. It is associated with development of anaemia in malaria and haemoglobinuria in babesiosis. 3. Type-III (Immune Complex disease): Circulating antigen antibody complexes (IgG or IgM) coupled with complement are deposited in tissue space causing damage to the tissues, e.g., glomerulonephritis in babesiosis, malaria, and granuloma formation around eggs of schistosomes. 4. Type-IV (Delayed): Biting fleas secrete saliva into the skin wound and some low molecular weight components present in the flea saliva act as haptens by binding to dermal collagen resulting in local type IV hypersensitivity reaction characterized by mononuclear cell infiltration. This is commonly known as flea bite dermatitis. However, in some sensitized animals, after some months, type I reaction takes over resulting in eosiniphil infiltration. Kinds of parasitic antigens 1. ES antigens: Antigens from the excretions (E) and secretions (S) of the parasite are called ES antigens. 2. Somatic antigens: Antigens elaborated by the entire body of the parasite is called somatic antigen. 3. Internal antigens: Antigens obtained after the disruption of the parasites. 4. External antigens: Antigens manifested by intact parasites. 5. Released antigens: Metabolic products of parasites are released antigens and these are comparable to external antigens. 6. Concealed or Hidden antigens: Antigens present on the intestinal surfaces of helminths and arthropods which are not recognized by the host. However, these concealed antigens are excellent targets for artificially induced responses. Evasion of immune response Helminths and protozoa have the capability to survive within immunologically competent host and can thus evade the host’s immune response by various mechanisms: 1. Parasite location in sanctuary sites: There is failure of phagosome fusion with lysosome (Toxoplasma gondii), escape into cytosol (Trypanosoma cruzi) or resistance to lysosomal enzymes (Leishmania sp.). In Toxoplasmosis, host antibodies are protective but the cystic stage of Toxoplasma is inaccessible to the humoral factors, hence the antibody cannot escape the cystic stage; as a result the overt clinical disease is rare but subclinical infection is relatively frequent. 2. Antigenic variation: In trypanosomosis and malaria, the parasites escape from the cytocidal action of humoral antibody on their cycling blood forms by altering their antigenicity. 3. Antigenic mimicry: In Schistosomosis, the host tissue materialgets attached to the surface of parasite and the host immune system fails to recognise the antigen to elicit immune response. Sometimes, antigenic determinants of parasite resemble host determinants and will not be recognised as ‘non self’ by the host and thus no immune response will be produced against them. Effect of immune response/ immunity on parasites 1. Prevention or reduction in the rate of establishment 2. Structural or metabolic alterations in the parasites 3. Retardation or inhibition of development, for example adult female Ostertagia ostertagi recovered from immunized calves show absence of vulvar flaps as compared to those recovered from non-immunized calves. 4. Inhibition of reproduction, for example in ticks that fed on immunized animals there will be extended oviposition, reduced egg laying and diminished hatchability of eggs. 5. Destruction of parasites in situ.  6. Elimination of existing infection. Harmful effects of parasites on their hosts Parasites have different types of effects on their hosts. Variability in the degree of harmful effects amongst various parasites is related to their number, invasive power, virulence, reproductive potentiality, propensity of release of toxic products and their localistaion in the body of their hosts, besides many other intrinsic and extrinsic factors in their surrounding within and outside of their hosts like general health condition, age, breed, sex, nutritional level, concurrent infections, state of hygienic condition,etc. The following types of pathological conditions are caused by different parasites:- 1. Compete with the host for food including vitamins (e.g. ascarid roundworms, tapeworms like Diphyllobothrium latum). 2. Decreased utilization and absorption of nutrients. 3. Reduction in the feed intake by the animals. 4. Increase in the passage of food, without proper digestion, through the digestive tract of animals. 5. Changes or reduction in the absorptive surface of the intestine (intestinal nodular worm of ruminants e.g. Oesophagostomum spp., Paracooperia nodulosa in buffaloes etc.) 6. Decreased synthesis of protein in skeletal muscles. 7. Alterations in the efflux and influx of water and sodium and chloride ions into the bowel (gastrointestinal nematodes). 8. Morphological and biochemical changes in the epithelial cells and their microvilli (e.g. coccidia). 9. Removal of host’s body fluid including blood (e.g. hookworms, ticks etc.). 10. Parasites feed on host’s solid tissues (kidney worm, liver fluke, immature amphistomes). 11. Destruction of host’s tissue mechanically or by pressure of the growing size of the parasite (Cysticercus, hydatid cyst etc.). 12. Cause mechanical obstruction of gut lumen, air passages, ducts, blood vessels etc. (e.g. ascarid worms, lungworms, liver fluke etc.) 13. Destroy host cells like epithelial, endothelial, connective tissue, RBC, WBC (e.g. coccidian, Babesia, Theileria etc.). 14. Produce toxic substances causing haemolysis, neurotoxin, anticoagulants, toxic metabolites etc. (e.g. hookworms, tapeworms, ascarids).  15. Various host’s tissue reactions against parasites like inflammation, haemorrhage, necrosis, fibrosis, excessive mucus production, nodulation, tumor formation, atrophy, paralysis, swelling, blindness etc. 16. Immune responses to parasites to include immunopathological lesions (e.g. eosinophilic granuloma around eggs of blood flukes; auto-immunity in piroplasmosis). 17. Some worms carry pathogenic organisms (e.g. Heterakis gallinae transmits Histomonas meleagridis, Metastrongylus apri carries swine influenza virus). 18. Parasitic infections depress immune system of animals making them susceptible to other pathogens (e.g. trypanosomosis, theileriosis etc.). General control measures against parasites The following measures should be kept in mind to prevent healthy animals from getting infection: 1. Animals should be kept in hygienic and in dry surroundings. 2. Avoiding access of susceptible animals to various sources of infection including contact with diseased animals. 3. Providing balanced nutrition and clean drinking water. 4. Removing spots/ places of breeding of intermediate hosts/ vectors including their killing by using molluscicides/ insecticides. 5. Proper maintenance of slaughter houses and effective disposal of offals/ blood accessible to stray animals. 6. Proper investigation of new animals before introducing in the herd/ flock. 7. Use of sterilised equipments for mass vaccination, artificial insemination, feeding, watering, storing etc. 8. Frequent screening of animals to detect any latent/ carrier case and its immediate treatment. 9. Formulating mass drenching schedule for prophylaxis according to the requirement in the area against possible parasitic infection and to remove infection from sub-clinical or carrier cases, particularly at organised livestock farms. Frequent removal of ticks from the body of animals and their immediate burning. 10. Newly born and young growing animals should be reared separately from the adult animals and they should not be allowed to graze on infected pastures. 11. Segregation of clinical cases and their proper treatment (chemotherapy). 12. All apparently healthy animals should be given preventive medication (chemoprophylaxis). 13. Vaccination where available and possible will also be helpful in curbing the disease.  Lecture 1 (Eucestoda) All parasites are classified into three major groups – Helminths, Arthropods and Protozoa. Helminths : Name helminths is derived from a Greek word helmins or helminthos which means a worm and this is applied to only parasitic and non parasitic species belonging to phylum Platyhelminthes and phylum Nemathelminthes. The annelids (leeches, earthworms etc.) are fundamentally different and not regarded as helminths. Characteristics of Phylum platyhelminthes : 1. The members of this phylum are dorsoventrally flattened and usually hermaphrodite with solid bodies. 2. They do not have body cavity. The organs are embedded in the parenchyma. 3. Respiratory and blood vascular systems are absent. 4. Flame cells are the excretory organs. 5. Like Nemathelminthes they are not metamerically segmented. 6. Life cycles are usually indirect. Phylum platyhelminthes further divided in to four classes. Class: Trematoda ; Class : Eucestoda ; Class : Turbellaria ; Class :Cotyloda. 1.Class: Trematoda :The parasites under this class have alimentary canal. Species are parasitic in man and animals.Commonly they are called as flukes. Further they are devided into two sub classes :1. Sub class- Digenea. 2. Sub class- Monogenea. 2. Class: Eucestoda: They are true cestodes.They do not have alimentary canal.Food is absorbed through the surface tegument. Commonly they are called as tape worms. 3. Class:Turbellaria : This class mainly comprised of the non parasitic species living in fresh water,sea water or on the land.These species have ciliated covering on their body.The species which are parasitic ,they are non parasitic in domesticated animals. 4. Class:Cotyloda : Shape of these parasites looks like tape worms. Forms are mainly parasitic in fishes except few (Diphyllobothrium & Spirometra sps.) whicg are parasitic in animals and man. Wardle et al.(1974) divided the cestode into two classes. ; Cotyloda and Eucestoda. The class Eucestoda contains 15 orders, of which 7 contain important parasites of domestic animals, man and fishes. Class: Eucestoda They are true cestodes.They do not have alimentary canal.Food is absorbed through the surface tegument. Commonly they are called as tape worms.  Cestus’ – Tape like structure.  Tapeworms are hermaphrodite.   They are endoparasites, elongate and flat in nature. Few millimeter to several centimeter in length.  Body cavity, digestive, respiratory and circulatory systems are absent.  Saprozoic nutrition.  Tape worms have 3 important parts,  Head or scolex: Scolex is usually globular in shape. Has four suckers(acetabula) , which may be armed with hooks. A protrusible part ; the rostellum, often armed , may be present.  Neck  The remainder body is called as strobila which consists of number of segments called as proglottids. Proglottids are vary in shape and size and are separated by transverse constrictions. Each proglottid contains one or two sets of reproductive organs. Majority of tapeworms have metameric repetition of their reproductive organs called as proglottidization. Proglottids are formed from neck/growth region and mature segment are pushed away from the scolex. The posterior proglottids when fully mature are packed with eggs and are called as gravid segments The body of tapeworms covered with tegument composed of syncytial outer layer formed by tegumental cells. The outer cytoplasm is extended into microtriches &microvilli (which are spine like processes covered with plasma membrane) containing micro tubular structure. The whole act as absorptive surface. Excretory system: Consists of Nephridial system with flame cells There is a presence of efferent canals ,usually on the either side two longitudinal canals joined by a loop in the scolex. Each pair may be connected in the posterior portion of the proglottids. Nervous system: Central part of the nervous system is situated in the scolex generraly consists of a rosteller nerve ring and two lateral nervous ganglia, from which six cords run posteriorly. In addition to that there is a dorsal and ventral nerve cords. Reproductive system: There are one or two sets of reproductive organs per proglottids. Mature proglottids are those in which reproductive organs are fully mature and functional. Following fertilization of eggs , the reproductive organs degenerates leaving gravid proglottids full of eggs. Gravid proglottids are detached from the worm and passed out of the host singly or in chains. Eggs set free by disintegration of gravid proglottids. The process is called apolysis. In some species (eg. Taenia) the eggs are released by pressure of eggs in uterus and the muscular activity of proglottids through an opening called as thysanus created in the uterus when gravid proglottid break away from strobila. When egg production ceased the exhausted proglottids detached from strobila and disintegrated , the process is called as pseudoapolysis. In cotyloda the proglottids are not detached and eggs are normally discharged from proglottids through an uterine pore opening on ventral side of proglottid. Male reproductive organs developed first and it is termed as protandry or androgyny Male reproductive system There is one/more but usually more number of testes. These testes discharge in vasa efferentia which join to form vas deference and ends in cirrus which is surrounded by cirrus sac. Male and female genital pore lies close together in genital sinus on lateral or ventral side. Self fertilization or cross fertilization between proglottids may occur. Female reproductive System Female genital pore leads to vagina Receptaculum seminis. Ovary is usually bilobed. Vitellaria is compact in Eucestoda May be follicular in cotyloda Uterus arises from ootype. The uterus in cotyloda may have pore which communicate outside In eucestoda it is filled with eggs. Uterus (in eucestoda) may be found as a tube or diverticula or may develop branching (Taenia). In gravid segments uterus may degenerate and eggs may pass singly or may pass, in groups, in a protective structure with in the segment. Protective structure such as hyaline egg capsules which enclose and protect the group of eggs. This structure is formed from uterus. Paruterine organs made up of fibro-muscular tissue of parenchyma and dilation of uterus. Eggs when passed out of the host may be embryonated or unembryonated. Embryonated eggs contain onchosphere armed with three pairs of hooks. Hatching and activation of onchosphere occur in the intestine of the intermediate host. Hatching may be by a combination mechanical action of the host and digestive enzymes (Taenia sp.). The activated onchosphere penetrate the intestinal mucosa and migrate to the site of predilection via circulation. General Life cycle of cestodes (tape worms): In majority of cases tapeworms are found in intestine of animals and man. Therefore the eggs or gravid segments are found in the faeces of infected animals. In majority of cases these eggs contain hexacanth embryo or onchosphere. Onchosphere do not hatch from the eggs unless the eggs have been swallowed by the intermediate host. Different species of invetebrate and vertebrate host act as intermediate hostfor different species of the tapeworms. 1) Life cycle of tape worm having invertebrate host as intermediate host: In this life cycle the eggs are swallowed by different species of invertebrate animals (Oribated mites ,flies ,fleas, ants beetles, earthworm etc.) which act as intermediate host. In the gut of these intermediate hosts eggs hatch and onchosphere released which subsequently penetrate the gut wall and reach to the body cavity In the body cavity the onchosphere converted into infective stage called cysticercoids. Final host acquire infection by swallowing infected invertebrate hosts containing cysticercoids ,with contaminated food and water. In the intestine of final host cysticercoids are releasedand scolex attach to the intestinal mucosa. Lateron by the process of proglottidization adult tapeworms are formed. 2) Life cycle of the tapeworms having vertebrates as intermediate hosts: In this life cycle eggs are swallowed by the herbivorous (cattle, sheep, goat, buffalo) omnivorous (pigs) and man which act as intermediate hosts.In the intestine of intermediate host eggs hatch and onchosphere released which invade the intestinal mucosa to reach in the blood circulation from where they are distributed throughout the body of Intermediate host. Only those onchosphere survived which reach to skeletal muscle, cardiac muscle and visceral organs depending upon the species of the tape worm. These later on develop into infective stage called as cysticercus, strobilocercus, coenurus, hydatid cyst). These are called as bladder worms because of their typical appearance like cyst or bladder /balloon. The final host acquire infection by swallowing uncooked/partially cooked meat and visceral organs containing these metacestodes. In the body of final host the scolices are released in the intestine and attach themselves to the intestinal mucosa and adult tapeworms are formed by the process of proglottidization. Types of metacestodes 1. Cysticercus Single invaginated scolex with cavity filled with fluid. Eg. Cysticercus cellulosae - larval stage of Taenia solium. And Cysticercus bovis - larval stage of T. saginata 2. Cysticercoid  Single non-invaginated scolex with drawn into a small vesicle. Practically no cavity.  Eg. Larval stage of ruminant and poultry tapeworm, Moniezia expansa has oribated mites as intermediate host. 3. Strobilocercus  A single scolex which is not invaginated when fully developed and attached with the bladder by a long neck.  Eg. Larval stage of Taenia taeniaeformis. 4. Coenurus   A large fluid containing bladder in which number of invaginated scolex attached to the wall.  Eg. Larval stage of Taenia. multiceps. 5. Hydatid cyst  Large fluid containing bladder it can produce daughter cyst is called as “Brood capsule” in which the scolices are develop. The mature brood capsule detached and float free in the fluid is called as “hydatid sand”.  Eg. Larval stage of Echinococcus granulosus. 6. Procercoid  Is the larval stage of Cotylodan tapeworms which is occurs in the first Intermediate Host.  Procercoid is solid body and possess hooks on the posterior region/cercomere e.g.Diphyllobothrium latum 7. Plerocercoid  Is also larval stage of Cotylodan tapeworms which occurs in the second Intermediate Host.  It is elongated, solid and has a scolex like in adults e.g. Diphyllobothrium latum. 8. Tetrathyridium It is a larval stage of Mesocestoides lineatus. The body is elongate, solid and has a deeply invaginated Scolex. Class Cotyloda Contains the parasites which are important in fishes in the plerocercoid or adult stage of the parasite except Diphyllobothrium and Spirometra species which are parasitic in man ,dog and cat. Eucestoda Cotyloda Hold fast organ is known as suckers. Suckers may be Hold fast organ is known as Bothria, two armed or unarmed and 4 in numbers. longitudinal weak muscular grooves. Segmentation is present. Segmentation is absent. Genital pore is present on the lateral aspect. Genital pore is on ventral aspect. Eggs are embryonated when laid and hatch out within Eggs are unembryonated, operculated and hatch out I/H.eg. Taenid egg in the water.eg. Diphyllobothrium latum egg It requires only one I/H It requires two I/H. Apolysis is present. Apolysis is absent.  Class Eucestoda Order: Anoplocephalidea Characters:  They do not have rostellum or hooks  Segments are usually broader than the length  Each set has one or two sets of genital organs  Genital pore located at the margin of the segments  The transverse uterus may persist or replaced by eggs capsule or one or more paruterine organs. Eggs have three covering, outer most vitelline membrane, a middle albuminous coat and inner most chitinous membrane which is frequently pear shaped bearing one side a pair of hooked projection called pyriform apparatus. Family -Anoplocephalidae  Uterus persists as transverse tube or network of tubes.  Intermediate hosts are oribatid mites. TAPE WORMS OF EQUINES Genus Anoplocephala Species A. perfoliata  Found in large intestine and small intestine of horse and donkeys.  Cosmopolitan in distribution and common species in horses.  Adult are up to 5 cm. Or up to 8 cm. And 1.2 cm. In width.  The scolex is 2-3 mm. In dia. And provided with lappet behind each sucker  Segments are wider than long & contain one set of reproductive organs.  Gravid uterus is transverse sack like and lobed.  Eggs measure 50-60 µm. Species: Anoplocephala magna  Found in small intestine (jejunum )and stomach of horse and donkeys.  They may reach to 80 cm X 2.5cm.  Scolex is 4-6 mm (large) & without lappets.  Eggs measure 50-60 µm. Genus Paranoplocephala Species P. mamillana  Found in small intestine, occasionally in stomach of equines.  They are 6-50 X 4-6 mm. In measurement.  The scolex is narrow.  The opening of the suckers is slit like situated dorsally and ventrally.  Lappets are absent.  Eggs measure 51 X 37 µm.  Life cycle  Gravid segments are passed out with the faeces. They are eaten up by oribatid mites (I.H.) in which cysticercoid develop in 2-4 months after infection.  Adult tapeworms are produced in the D.H. in 4-6 weeks after accidental ingestion of the infected mites during grazing. Pathogenesis: Light infection goes unnoticed but heavy infection may cause ill health, unthriftiness and even death.  A. perfoliata usually found near the ileo-caecal orifice so here it may cause dark depressed ulcerative lesions. There may be oedema and granulation tissue and rarely occlusion of ileocaecal orifice. A. magna if present in large number, may cause haemorrhagic / catarrhal enteritis. Perforation of intestine has been recorded by A. perfoliata and A. magna. P. mamillana is usually not causing ill health. Diagnosis By finding the eggs in the faeces of the host Treatment: Niclosamide @ 88 mg./KG. B.Wt. Bithional @ 7mg. / Kg. B. Wt. Micronised mebendazole @ 15-20 mg/kg. b.wt. Egg life cycle  L=lappets S=suckers Anoplocephala perfoliata  TAPE WORMS OF RUMINANTS Genus: Moniezia Species : Moniezia expansa Found in small intestine of sheep, goat, cattle and other ruminants. Cosmopolitan. Measurement; 600cm.X 1.6cm. , scolex - 0.38-0.8 mm. Wide ,have prominent suckers. Rostellum and hooks are absent. Segments are broader than long and each segment contains two sets of reproductive organs with genital pore at the margins. Ovaries and vitelline glands form a ring on both sides median to longitudinal excretory canal. Testes are distributed throughout the central field. Interproglottidal are rosette like found at the posterior border of the segment and extended across the width of the proglottid. Uterus becomes sac like when filled with the eggs. Eggs roughly triangular in shape contain well developed pyriform apparatus. Eggs measure 56-67 um. Genus: Moniezia Species : Moniezia benedeni Small intestine of cattle , other ruminants. It is broader (2.6cm.) than M. expansa. Interproglottidal glands in a short continuous row close to midline of the segment. Life cycle: Gravid segment in faeces → eggs eaten by oribatid mites (I.H.) →cysticercoids develop in mites in 4 months → animal is infected by eating of mites when grazing. P.P. 37-40 days. Infection is common in calves/ lambs/kids in first summer on pasture. Lambs may start passing ripe segments in faeces at the age of 6 week. Pathogenesis: Infection is common in lambs, kids and calves under 6 months age. May cause diarrhoea, unthriftiness, obstruction of intestine, depressed wool and meat production. Light infection has no clinical significance. Diagnosis: Faecal Examination Gross examination may reveal Cooked rice like segments. Eggs are square in shape with pyriform apparatus Treatment: Niclosamide 75mg./kg. , Praziquantel 15mg/kg. , Fenbendazole – 5mg/kg., Cambendazole 20 mg./kg. Albendazole 10 mg./kg. Moniezia expansa mature segment Moniezia benedeni egg  Moniezia benedeni (mature segment) Family : Thysanosomidae In the members gravid uterus disappear and replaced by paruterine organ or capsule Genus : Avitellina Species: A. centripunctata Small intestine of sheep and other ruminants. Prevalent in Europe, Africa and Asia. Size: 300cm.X3mm. They are cylindrical in posterior end. Segments are short and not distinctly segmented. Genital organ is single set and G.P. Alternate irregularly. Uterus lies transversely in middle portion. Uterus and par uterine organs show a opaque line in the middle portion of segment. Eggs without pyriform apparatus measuring 21-45 um. Life cycle: Psocids(bark lice, dust lice, book lice) may serve as Intermediate host in which the cysticercoid develops. Pathogenesis: same as Moniezia, considered to be less pathogenic. Treatment: Bithional, praziquantal and niclosamide are given with same dose rates. Genus : Stilesia Species: Stilesia hepatica Found in the bile ducts of sheep, goat, cattle and wild ruminants in Africa and Asia. In Africa 90-100% sheep may be infected. Adults are 20-50 cm long and 3 mm wide. It has broad neck and prominent sucker. Proglottids are short. Reproductive organs are single set and genital pore alternate irregularly. Uterus long transverse and dumbel bell-shaped Eggs pass into two paruterine organs each containing about 30 eggs. Eggs have pyriform apparatus measuring 26x 16-19 um Life cycle: Oribatid mites act as intermediate hosts Pathogenesis: Occurs in animals of all ages groups. In light infection non pathogenic, in heavy infection may cause slight cirrhosis. In most of the cases where whole bile ducts may be full of worms even these worms form dilatations but no icterus or other clinical signs are seen. Infected liver is condemned during meat inspection. Treatment: praziquantel - @ 15 mg./kg. Genus : Stilesia Species: Stilesia globipunctata Small intestine of sheep , goat, cattle & other ruminants. Common in Europe, Africa and Asia. Morphology: Adult are 45-60 cm long and 8.5 mm wide. Characters same as S. hepatica except testes are arranged in two rows on lateral side of lateral canals. Life cycle: Psocids and oribatid mites act as intermediate host in which cysticercoid develop. Pathogenesis: They are attached at the junction of duodenum and jejunum. Scolex of immature worms penetrate in the mucosa of intestine. At the site of the attachment there is nodule formation, cell infiltration, proliferative inflammation and desquamation of epithelial cells. Scolex and anterior part of segments are embedded in mucosa and rest of tapeworm is found free in the lumen. Treatment: Praziquantel @ 15 mg/ kg body weight. Thysanosoma actinoides Called as fringed tapeworms and found in bile ducts, pancreatic ducts and small intestine of sheep, cattle and deer in western part of USA and South America Size:15-30 cm x 8mm, scolex 1.5 mm segments are short and fringed posteriorly Each segment contains two sets of genital organs and testes lie in the median field. Uterus is single undulating tube. Eggs pass in several paruterine organs each containing 6-12 eggs. Eggs do not have pyriform apparatus Life cycle: not well understoodnot well understood possibly cysticercoids develops in psocids. Pathogenesis: It may obstruct the flow of bile and pancreatic juice and cause digestive disorders and unthriftiness. Infected liver is liable to be condemned. Treatment : Bithional @ 200mg./kg, niclosamide @ 400mg./kg, praziquantel @ 15 mg./kg Genus : Thysaniezia Species: Thysaniezia giardi It occurs in the small intestine of sheep, goat and cattle of Europe, Russia, Africa And America. Morphology Size 200 cm x 12mm wide Short segments Single pore Gential pore alternate irregularly The side of the segments, cirrus sac bulges out, thus the margins seem to be having irregular appearance  No pyriform appartus Eggs pass from uterus to a large number of par uterine organs Life cycle Psosids act as intemediate hosts Pathogenesis Infect both large and small animals but rarely produce clinical symptoms Treatment:Same as Moniezia sp.  TAPEWORMS OF POULTRY ORDER: Davaineidea. Small to medium sized tapeworms. Rostellum is retractable and armed with numerous hammer shaped hooks. Suckers are usually armed. Genital organs are usually single. Uterus may persist or eggs may pass into egg capsule or in paruterine organ. Family: Davaineidae In this family uterus is replaced by egg capsule. Genus: Davainea Davainea proglottina Common name Dwarf tapeworm of poultry Host Chicken and pigeon Location Duodenum I/H Slug (snail without shell). Limax and Arion species Morphology  The worms are microscopic in nature, about 0.5 to 3mm in length. They have only 4 to 9 segments.  Rostellum is retractable and armed with hammer shaped hooks.  Suckers also armed with hooks.  Each segment has single set of genital organ.  Genital pore opens regularly alternate.  In the gravid segment, the uterus is replaced by egg capsule. 1   Each egg capsule contains single egg.  Eggs are 28-40 um. In diameter  Raillietina tetragona Common name Largest poultry tapeworm Host Chicken, pigeon and guinea fowl Location Posterior half of the small intestine I/H Ants. (Pheidole spp. and Tetramorium spp.) Morphology  Adults are up to 25 cm in length. Scolex is smaller than the R.echinobothridia. Rostellum is armed with 1 to 2 rows of hooks. Suckers are oval in shape and armed with hooks.  Each segment has single set of reproductive organs genital pore opens unilaterally.  Each egg capsule contains 6 to 12 eggs.  found in posterior half of small intestine of poultry guinea fowl, pigeon and other birds..  Cosmopolitan in distribution.  It is one of the largest fowl tapeworm and may reach 2   up to 25 cm in length.   R. echinobothridia Host Chicken and turkey Location Small intestine I/H Ants. (Tetramorium spp.) Causes Nodular taeniosis  Scolex is large in size when compared to R. tetragona.  Rostellum heavily armed with two rows of hooks. Suckers are circular in shape.  Each segment has single set of genital organ. Genital pore irregularly alternate  Gravid segments are separated by windows in progottids.  Each egg capsule contains 6 to 12 eggs. 3 R. cesticillus Host Chicken Location Small intestine I/H Dung beetles Morphology  Usually 4 cm in length. Rarely it attains 15 cm. Scolex is very wide.  Large rostellum armed with 400 to 500 small hooks.  Suckers are indistinct and are not armed.  Each segment contains single set of genital organs. Genital pore unilateral.  Each egg capsule has single egg. 4   Cotugnia digonopora Common name Double pored poultry tapeworm Host Chicken Location Small intestine I/H Ants. (Pheidole spp., Monomoriumfloricola) Morphology  Rostellum is armed with two rows of hooks.  It has cup like muscular suckers.  Each segment contains two sets of genital organs.  Eggs capsule contain single egg. 5   Order – Dilepididea Amoebotaenia sphenoides 1. Rostellum is armed with two or more rows of rose thorn 2. shaped hooks. 3. Sucker are armed. Genital organs are single or double sets. 4. Uterus may be sac like or eggs pass in capsule or par uterine organ. 5. The species are found in birds. Family_ Dilepididae: Uterus persists as transverse sac. Host Chicken Location Small intestine 6  I/H Earthworm Morphology  Small worm. Elongate triangular shape. 4 mm long and 1 mm wide.  Rostellum bears 12-14 hooks.  There are about 20 proglottids.  Testes are 12 or more in number and lie near the posterior border of the segment.  Uterus is sac-like and slightly lobed.  Family : Dipylidiidae  In the members gravid uterus is replaced by egg capsule containing one or more eggs. Genus : Choanotaenia Species: C. infundibulum  Found in the upper half of small intestine of fowl and turkey.  Size: up to 23 cm. Segments are wide posteriorly  Rostellum is armed with 16-20 slender hooks.  G.Pore alternate regularly.  Uterus is sac like.  Proglottids leave host before maturity Life cycle: Musca domestica and beetles of genera Calathus & Tribolium act as I.H 7 Hymenolepis carioca Host Chicken Location Small intestine I/H Dung bettles, flour beetles and Stomoxys calcitrans Morphology  Rostellum armed with spanner shaped hooks.  Segments are very small. Each contains single set of reproductive organ. Genital pore is unilateral.  Each segments contains three testes. One testes on poral side while the other two on aporal side.  Eggs are covered with 3 layers and is rugby ball shaped. Host Ducks Location Small intestine 8  H. lanceolata I/H Aquatic crustaeceans Morphology  Similar to H.carioca. Life cycle  The gravid segments are passed in the droppings of birds and are crawling on the surface of droppings, during this process, eggs are released. Egg contains hexacanth embryo.  The eggs are ingested by intermediate hosts where they hatch and develops into cysticercoid in about 3 weeks time. Infection of poultry by ingestion of infected I/H. Prepatent period D. proglottina 14 days R. tetragona 21 days R. echinobothridia 20 days R. cesticillus 13 days C. infundibulum 15 days C. digonopora 20 days Hymenolepis spp. 20 days Epidemiology 9   Tapeworm infections are common in free range birds than the intensive system of rearing. Since free range birds have more access to eat I/H than birds reared under confined environment.  Sometimes heavy tapeworm infection occurs in intensive system of management due to this system provide conducive environment for breeding of I/H like flies, beetles and ants. Pathogenesis  D. proglottina is most pathogenic tapeworm. The worms are penetrate deeply between the villi causes necrosis and haemorrhagic enteritis. Sometimes death may occur due to intestinal obstruction.  Chronic infection characterized by reduced growth rate, emaciation and weakness.  R. echinobothridia is most pathogenic causes nodules formation in the intestine is called as “Nodular taeniasis” in poultry. Hyperplastic enteritis may also occur.  All other tapeworms are less pathogenic but in heavy infection results in reduced egg production and general weakness. Diagnosis, treatment and control Diagnosis  Macroscopic or gross examination of dropping for the presence of gravid segment.  PM examination of representative bird from affected flock. Treatment  Niclosamide - 75 mg/Kg b wt.  Fenbendazole - 5 mg/Kg b wt.  Aricolinehydrobromide (Arica nut).  Praziquantel - 15 mg/Kg b wt.  Closantel - 7.5 mg/Kg b wt. Control  Elimination of I/H is very important by: 10  Hygienic maintenance of poultry shed. Applying chemical compounds like BHC and HCH. Insect growth regulators like larvadex may be used against Musca spp. Laris (Cyromazine) - Chitin inhibitor may be used against I/H develop.  Periodical deworming of birds. 11  Order : Hymenolepididea  Small to medium sized tapeworms.  Rostellum is retractable with single circle of hooks.  Scolex has four unarmed suckers.  Single set of genital organs & genital pore unilateral.  Eggs have three delicate membranes.  Intermediate hosts are arthropods in which cysticercoid develops. Family : Hymenolepididae Genus: Hymenolepis Species H. nana (Dwarf tapeworm of man) 1. Found in small intestine of man and rodents. 2. They are 2.5-4cm. Long. 3. Eggs are oval; onchosphere has three pairs of hooks. It is most common tape worm of man in tropics and sub tropics. Life Cycle: Direct. In man cysticercoids develop in villi of small intestine and emerge out and develop in lumen as adult. P.P. 16 days. Auto infection has been recorded. In rodents life cycle can be direct or indirect where flour beetles and fleas act as intermediate host. Pathogenesis Heavy infection in man may cause anorexia, vomition, diarrhea and pain Diagnosis: eggs in faeces. Treatment: Rodents: Niclosamide 100-200mg/kg body weight in rats and hamster Bunamidine hydrochloride 200mg/kg bodyweight Praziquantel: 25 mg/kg body weight.  Hymenolepis nana egg Order Dilepididea Family: Dipylidiidae Genus : Dipylidium Species: D. caninum  Found in S.I. of dogs, cat, fox and occasionally in man.  Worldwide in distribution,   commonest species in dogs. Dipylidium caninum Common name Double pored dog tapeworm. It also occurs in man and cat. Location Small intestine I/H Dog flea: (Ctenocephalides canis), Dog lice: Trichodectes canis and Heterodoxus spiniger) Metacestode stage Cysticercoid Morphology  Retractable rostellum armed with three or four rows of rose thorn shaped hooks.  They are upto 50cm  Each segment contains two sets of genital organ.  Vitelline glands and ovary form a mass on either side resembling a bunch of grapes.  In the gravid segment uterus are replaced by egg capsule or egg packets.  Egg packets contain 30 eggs per packet. Gravid segments are elongate and oval in shape resembling cucumber seed shape. Life cycle   The gravid segments are passed in the faeces or spontaneously leaving the host and crawling on the body surface of the host or on the floor, during this process eggs are released.  Eggs are ingested by larval stage of fleas, but cysticercoid development occurs in the adult flea.  D/H acquires infection by ingestion of infected adult flea.  Man acquires infection by accidental ingestion of flea while playing with dog and cat. Egg ----> Larval flea ----> Adult flea ---->D/H Pathogenesis  It depends upon the age of host. Adult worms are not pathogenic to dog but heavy infection causes abdominal pain, unthriftiness, diarrhoea or constipation and rarely intestinal obstruction may occur.  When gravid segment leave the intestines they cause severe irritation around the perianal area and due to constant irritation the dog will drag its anus over the ground. This condition is known as “anal pruritus”. Diagnosis and treatment Diagnosis  Demonstration of egg packets in faeces.   Macroscopic examination of feaces for gravid segment. Treatment  Arecolinehydrobromide - 1 to 2 mg/Kg b wt.  Praziquantel – 5 mg/Kg b wt.  Niclosamide – 100 to 150 mg/Kg b wt.  Mebendazole – 100 to 200 mg/Kg b wt. Twice daily fo 5 days.  Bithionol – 200 mg/Kg b wt. Dipylidium caninum eggs  ORDER : Taeniidea It contains usually large tapeworms. Gravid segments are longer than wide. Rostellum may be absent or present (armed with double row of small and large hooks). Genital pore are single and alternate irregularly. Testes are in large number. Ovary in the posterior part of the segment. Uterus has median longitudinal stem and lateral branches. Eggs has outer envelop, inside it is inner envelope which develops into embryophore which is made of blocks and give characteristic appearance to eggs within this is present onchospheral membrane which surrounds the hexacanth embryo. Metacestodes are cysticercus, Strobilocercus, coenurus or a hydatid cyst. Genus: Taenia Species: Taenia saginata Tapeworm is found in small intestine of man and cysticercus (metacestode) is found in cattle. Other animals such as llama, and reindeer may also serve as intermediate host. T. saginata survive many years in definitive host & cosmopolitan in distribution. It is most important in Africa, South America and Mediterranean countries. Morphology: Adult worm is 4-8 meter long and may reach 25 meter. Scolex has 4 suckers without hooks. Rostellum is absent. (present in T. solium with 2 rows of hooks) Gravid segment contains 80000 eggs. (40000 in T. solium) Uterus has 14-32 lateral branches. (7-16 in T. solium) Vaginal sphincter muscle is present (absent in T.solium) Cirrus pouch does not extend to excretory vessel (reach in T. solium) Ovary is bilobed (trilobed in T. solium) Gravid segments leave host spontaneously (In T.solium they do not)  A=scolex, B=gravid segment, C= mature segment Life cycle: About 10 segments are shed daily which migrate out of anus. They are motile and migrate for few centimeters over body, clothed, grounds or beds and discharge the eggs. The eggs remain viable for several weeks- months in sewage in river or pasture. By variety of ways neonatal calves become infected such as if they are handled by infected person who also disperse eggs in pastures. The places which are closely infected are camping ground, spots visited by tourists, irrigation ditches, hay fields etc. Eggs can survive for 71 days in liquid manure, 16 days in city sewage 33 days in river water and 159 days on pastures. When eggs are ingested by cattle→onchosphere hatch→after activation by gastric and intestinal juice penetrate intestinal mucosa to reach in general circulation→disseminated throughout body and skeletal and cardiac muscles, in fat and other organs. Cysticerci are found in all muscles but muscles of heart, messeters, diaphragm and tongue have highest concentration of Cysticercus bovis. Cysticerci become infective in 10 weeks and remain viable for 9 months or longer. Man is infected by ingestion of raw or under cooked infected (measly beef) gravid segmens start passing after 100 days. Cysticerci degenerate 4-6 months after infection and by 9 months large number may be dead.  In neonatal calf, cysticerci remain viable for longer period perhaps for whole life. Taenia solium Small intestine of man. The pigs and wild boars act as intermediate host. Man act as definitive host. Morphology: Adults are 3-5 meters long and may reach 8 mater and may survive for 25 yars. Scolex bears a rostellum which has 2 rows of hooks. Gravid segment 10-12 meter long and 5-6 mm wide. Uterus has 7-16 lateral branches. Vaginal sphincter muscle is absent. Cirrus pouch reach to excretory vessel. Ovary is trilobed in T solium. Gravid segment has about 40,000 eggs. Gravid segments do not leave host spontaneously and voioded in facese in chain. Eggs are 26-34 μm in diameter in T. saginata they are 46-50 by 39-41 μm  Life cycle Life cy