Cestoda Veterinary Helminthology PDF

Cestoda VPar 102 – Veterinary Helminthology John Philip Lou M. Lumain, DVM, MSTAH Learning Outcomes: Introduction Belong to the Phylum Platyhelminthes Parasites of fish, amphibians, reptiles, birds and mammals Hermaphrodite Dorsoventrally flattened Indirect life cycl...

Cestoda VPar 102 – Veterinary Helminthology John Philip Lou M. Lumain, DVM, MSTAH Learning Outcomes: Introduction Belong to the Phylum Platyhelminthes Parasites of fish, amphibians, reptiles, birds and mammals Hermaphrodite Dorsoventrally flattened Indirect life cycle (1 to 2 IH) Long patent period Lack digestive system Body covered by an absorptive tegument Larval stages in intermediate host: metacestode  Two main groups: 1. Cestodaria - Non-important* - Possess 10 hooks (decacanth) 2. Eucestoda - Possess only six hooks Introduction (hexacanth) Important species of Euscestodes Important species of Euscestodes General features Body plan of most cestodes includes a scolex, neck, and a strobila Entire worm behind the scolex is collectively called the strobili. Unique reproductive segments known as proglottids = tissues (e.g., tegument and muscles) are continuous between each segment. As new proglottids are formed in the neck, the previous ones move posteriorly in a continuous process (proliferation zone) Diagrammatic representation of the scolices of different groups of tapeworms. General features In some species, eggs are shed from the strobila while the proglottid remains attached. When these egg-filled gravid proglottids are spent, they detach and rapidly disintegrate. Other species, the proglottid detaches before releasing the eggs and leaves the host intact with the feces. General features Almost all cestodes have many proglottids and are referred to as polyzoic. All of the reproductive organs and the scolex are within a single body, without a strobilla lacking all signs of segmentation: known as monozoic (Carynphyllidea). The cestode tegument is complex and multifunctional (roles in nutrition, attachment, evasion of host immunity, and protection from host digestion). Reproductive System Most cestodes are monoecious with each proglottid have one set of male organs and one set of female organs. 1. Moniezia expansa – duplicate set of male and female organs each proglottids. 2. Diplophallus – two sets of male and one set of female organs. Reproductive System Self-fertilization is usually avoided because: the male repro system matures before the female counterpart (protandry). Or the female repro organs matures before the male organs (protogyny). Transfer of sperm normally occurs between different proglottids* of the same strobili, or between proglottids in different strobilla. Reproductive System Reproductive System The cirrus is a protrusible copulatory organ that evaginates through the genital atrium. Sperm transfer normally occurs from the cirrus into the vagina. Some species however, lack a vagina. In these case, the cirrus is forced through the body wall and sperm are deposited into the parynchyma. Reproductive Organs 1. Male Testis Vas Deferens Seminal receptacle/ vesicle Cirrus (protrusible) 2. Female Ovary (germarium) Yolk stock (vitellarium) Ootype Mehlis’ gland Uterus Vagina Egg Formation 1. The ovary of the cestodes releases periodically. 2. The oocytes are fertilized inside the ootype by sperms coming from the receptaculum seminis. 3. Yolk cells (produced inside the vitellarium) are added inside the ootype to the zygote, and an eggshell is formed. 4. The fertilized eggs are released from the ootype and are pushed to the uterus. Ø Thick-walled, scletorized “eggs” with an operculum Ø Non- or low-graded scletorized eggs Egg Formation 5. The terminal gravid proglottids are released (apolitically) singly or in groups from the strobila (=chain of all proglottids). For example, in the case of the Taenia species about 3–10 proglottids become released at the same time and are excreted within the feces of the host. Ø Thick-walled, selectorized “eggs” with an operculum Ø Non- or low-graded selectorized eggs Egg Formation In the case of Diphyllobothrium spp., the eggs are already released still inside the intestine, so that the proglottids seen in the feces are empty and the typical eggs are mixed within the host’s feces. 6. This type of excretion of small bands of empty proglottids is described as “pseudo- apolytic”. Ø Thick-walled, selectorized “eggs” with an operculum Ø Non- or low-graded selectorized eggs Egg Formation 7. In other species, the proglottids are already in the intestine from the strobila just after fertilization. Such phenomena are described as euapolytic or hyperapolytic. Ø Thick-walled, selectorized “eggs” with an operculum Ø Non- or low-graded selectorized eggs  Takes two pattern: General Life Cycle Tapeworms that are mostly aquatic Tapeworms that are associated with one intermediate host and typically a terrestrial in nature.  For aquatic parasites Larvae hatches and develops to coracidium. Penetrates the fish gut and Within the eggs are the Either the egg or the enters the hemocoele. oncosphere or hexacanth coracidium are ingested Transforms into a procercoid (six-hooked) embryos. by the zooplankton containing a cercomer. microcrustaceans or fish intermediate host. Plerocercoid transforms into Final larvae reach the final adult. The life cycle is completed location (species-specific when the first intermediate locations) it will transform to hosts are eaten by avian or plerocercoid. mammalian definitive host. In the two orders: Diphyllpobothridea and Proteocephalidea = uses the zooplankton microcrustaceans such as the copepod as the first IH and fish as the second IH For aquatic parasites For terrestrial parasites HAS TWO LARVAL BODY PLAN Eggs ingested by Eggs release from the intermediate host which Release of the oncosphere and apolytic proglottids are invertebrates such as attaches the gut wall. (apolysis) insects Transform to cysticercoid in the hemocoele of the insect and awaits for the consumption of the DH. Life cycle pattern is normally associated with a single intermediate host, and is typically terrestrial. For terrestrial parasites HAS TWO LARVAL BODY PLAN Gravid proglottids are Eggs are retained in the ingested and the eggs are Release of the oncospshere and proglottids (anapolysis). release in the GIT after transform to cysticercus/bladder the disintegration of the worm. proglottids. DH eats the IH and the cysticerci The cysticerci are deposited in are eaten and the hooks the muscular part of the IH’s evaginates. It attaches in the body (e.g., heart, muscle, intestine of the host. tongue, etc.). Cysticerci has an invaginated scolex. Undergoes strobilation to form the proglottids. For terrestrial parasites For terrestrial parasites For terrestrial parasites  Life Cycle Comparison  Cysticercoid Metacestodes Cysticercus Metacestodes Metacestodes  References Goater, T. M., Goater, C. P., & Esch, G. W. (2014). Parasitism: the diversity and ecology of animal parasites. Cambridge University Press. Dorny, P., Schwan, V., Dermauw, V., Trevisan, C., Claes, L., & Van Hul, A. (n.d.). Applied veterinary helminthology: Introduction on helminths and helminthoses. Kaufmann, J. (1996). Parasitic infections of domestic animals: a diagnostic manual. ILRI (aka ILCA and ILRAD). Grist, A. (2013). Ovine Meat Inspection (2nd ed.). Anatomy, Physiology, and Disease Conditions.