Cestodes.docx

Cestodes: General Info Cestodes are in the phylum Platyhelminthes and are also known as “tapeworms”. Cestodes have a flat body and lack a body cavity (meaning that they lack intestines). Their flat body has segments of proglottids. They are hermaphroditic with both sex organs being present in each p...

Cestodes: General Info Cestodes are in the phylum Platyhelminthes and are also known as “tapeworms”. Cestodes have a flat body and lack a body cavity (meaning that they lack intestines). Their flat body has segments of proglottids. They are hermaphroditic with both sex organs being present in each proglottid. The cestode body includes the proglottids (segments), strobila (body), head, and neck. The cestode head (AKA: scolex): Has either 4 suckers or a bothria Can be armed or unarmed with hooks Most have a rostellum (mouth opening) The cestode body (AKA: strobila) has: Proglottids (segments) When counting the number of proglottids on a cestode, ensure to note the presence of the neck before starting the count of proglottids. Mature posterior (portion of the body furthest from the scolex is most mature/developed) The most mature proglottids are detached first. When cestodes are still alive, they are actively moving, and it can be difficult to accurately describe them. However, if you observe the most mature end of the cestode, you can give a more accurate description of the parasite’s proglottids. The cestode proglottids (segments) can have: Male and female reproductive organs Vitelline glands (which are used for species recognition) Genital pores When trying to identify a cestode species, it is important to not these features within the proglottid: The shape (is it bell shaped?) The width The length Whether or not fringe is present If there are 1 or 2 genital pores Where the glands are positioned Cestodes lack an alimentary canal, meaning that they absorb nutrients through their integument (skin) of each proglottid. Cestodes have an indirect life cycle which means that they require an intermediate host for their development. Cestodes have several types of larval stages, however there is only 1 type found per species. The adult stage of cestodes is ALWAYS found within the final host. When sending in pictures of a parasite to a specialist for identification, it is important to try to get the whole body of the parasite within the picture to determine the size of the parasite. Clinical Relevance: Some can be zoonotic Can cause clinical symptoms in young animals if the infection is heavy If “pearly beef” if present, the meat has to be condemned which can cause a financial loss for farmers. Larva invasion into the lungs or liver can cause illness in animals Cestodes do not rely on seasonality for infection because their host defecate all year long, which is their mode of infection, through the feces. Cestodes: Order Pseudophyllidea The order pseudophyllidea has 2 intermediate hosts, with the first IH being a crustacean. They use BOTHRIA and scolex for attachment to the host’s organs. Their eggs are contained in oncospheres but have cilia for motility. Cestodes: Order Cyclophyllidea Anatomy Cyclophyllidea only has 1 intermediate host (IH). They use (4) SUCKERS and scolex for attachment to the host’s organs. Their eggs are contained within an oncosphere. When trying to identify the specific species, it is important to note the following: The size of the sucker Whether or not the sucker has hooks The shape of the sucker Whether or not a rostellum is present Whether or not the rostellum has hooks All adult cyclophyllidea are ALWAYS found within the small intestines of their final host, regardless of the animal being used as the host. Their eggs look like they have finger bones within them. Cestodes: Order Cyclophyllidea Life Cycle Step 1: The adult stage is found within the final host (dogs) where they use their rostellum to stay attached to the host’s small intestines. Step 2: The proglottids are found within the feces (from the final host) where eggs are released from the proglottid. Step 3: The eggs are ingested by the IH (fleas) where the larvae will develop. The ONLY purpose of the larvae is to develop into a scolex so that the parasite can attach to the small intestines of the host. Step 4: The final host can ONLY be infected by CONSUMING the infected IH. Cestodes: Order Cyclophyllidea Pathogenicity The adult stage is typically not problematic, unless the infection is heavy, then diarrhea can be caused. Therefore, when dogs are dewormed for this type of tapeworm, it is solely for cosmetic reasons because the owner of the dog does not like seeing the proglottids in the feces, despite the parasite being relatively harmless. The larvae stage, if infected in humans, will cause the most damage. This can be zoonotic, but it is very uncommon. The major goal of this parasite is to release it’s proglottids into the environment. The proglottids are released as oncospheres or hexacanth embryo. Hydatic cysts: Echinococcus species When larva is found imbedded in the muscle of cattle, it is referred to as “pearly beef”. This species of tapeworm has humans as their final host, and cows as their intermediate host. The larva tend to imbed in the liver and lungs of the host. Cestodes: Taenia solium Normal Life Cycle They have a flattened shape and are hermaphroditic. The adult stage is only found within the small intestines of the final host. Clinical signs are rare within the final host. The only clinical sign would be having an itchy anus (AKA: Taeniasis). Proglottids are typically found within human feces- where the eggs can be oncospheres or hexacanth embryos. The final host (humans) can only become infected by EATING the infected IH (pigs). Humans typically gain infection by accidentally eating undercooked pork or by intentionally eating the “pearly pork” as it can be a delicacy in some parts of the world. The IH can have clinical signs of sickness. The IH gets infected by eating the hexacanth embryo within human feces. The larva develop within the pig and can commonly be found in the tongue or any other muscle of the pig. Larva embedded in the muscle of pigs is referred to as “pearly pork”. If few larva are present on the tongue, the diagnosis of infection can be missed. This parasite is not commonly found within the USA, however, it is found in South America and Africa. It is important to understand this parasite, because the parasite travels with it’s host, so it could travel to the USA. This parasite can grow to become several feet long. Cestodes: Taenia solium Abnormal Life Cycle If humans ingest infected human feces, they can become infected with this parasite. However, because there is no IH present for larva development, the parasite gets lost and migrates to the brain of the human and begins larval development there. The parasite develops into cysticercus. This can be extremely deadly and very commonly leads to epilepsy. Taenia solium is the number one most preventable cause of epilepsy. Humans act as an aberrant and dead-end host in this abnormal life cycle where the human is infected with the larval stage of this parasite. Larval infection in the human brain is referred to as NCC (neurocysticercosis). If the infection is very minimal, humans can successfully be treated.