Platyhelminthes/Cestoda
AThe parasitic worms, or helminths, of human beings belong to two phyla:
(1) Platyhelminthes (flatworms) lack a true body cavity (celom) and are characteristically flat in dorsoventral section. All medically important species belong to the classes Cestoda (tapeworms) and Trematoda (flukes).
(2) Nemathelminthes : worm-like, separate-sexed, unsegmented roundworms.
Cestoda (tape-worm): ex.Taenia
T. solium (the pork tapeworm)
T. saginata (the beef tapeworm)
Tapeworms are parasites of the intestinal tract whose simple life cycle requires at least one intermediate host, consists of two parts:-
1. Scolex: a rounded head. The scolex has specialized means of attaching to the intestinal wall, namely suckers, hooks, or sucking grooves. 2. Proglottids (a flat body of multiple segments). The worm grows by adding new proglottids from its germinal center next to the scolex. The oldest proglottids at the distal end are gravid and produce many eggs, which are excreted in the feces and transmitted to various intermediate hosts such as cattle, pigs, and fish.
The Scolex of T. solium gravid Proglottids of T. solium
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Platyhelminthes/Cestoda
Disease:-Adult form causes taeniasis -Larvae cause cysticercosis Taenia species life cycle
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Platyhelminthes/Cestoda
Cysticercosis-causing tapeworm life cycle
In cysticercosis, a more dangerous sequence occurs when a person ingests the worm eggs in food or water that has been contaminated with human feces. The eggs hatch in the small intestine, and the oncospheres burrow through the wall into a blood vessel. They can disseminate to many organs, especially the eyes and brain, where they encyst to form cysticerci.
Epidemiology:-
- The epidemiology of taeniasis and cysticercosis is related to the access of pigs to human feces and to consumption of raw or undercooked pork. - The disease is endemic in areas of Asia, South America and Eastern Europe.
Clinical findings:-
- Taeniasis due to T. solium or T. saginata is usually characterized by mild and non- specific symptoms. Abdominal pain, nausea, diarrhoea or constipation, 6–8 weeks after ingestion of meat containing cysticerci.
- These symptoms may continue until the tapeworm dies following treatment, otherwise it may live for years.
- In the case of cysticercosis due to T.solium, the incubation period is variable, and infected people may remain asymptomatic for years.
- In some endemic regions (Asia), infected people may develop visible or palpable nodules (a small solid bump or node which is solid that can be detected by touch) beneath the skin (subcutaneous).
- Symptoms of neurocysticercosis may include chronic headaches, blindness, seizures epilepsy, hydrocephalus, meningitis, dementia and symptoms caused by lesions occupying spaces of the central nervous system.
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Platyhelminthes/Cestoda
Lab. Diagnosis:-
- Identification of T.solium proglottids or eggs in the stool - Diagnosis of cysticercosis by presence cyst in tissue by surgical removal or computed tomography (CT) scan - Serological tests
Treatment:-
- The treatment of choice for intestinal worms is praziquantel. - For cysticercosis is praziquantel or albendazole. - In 2015, the WHO Foodborne Disease Burden Epidemiology Reference Group identified T. solium as a leading cause of deaths from food-borne diseases, resulting in a considerable total of 2.8 million disability-adjusted life-years (DALYs). - T. solium cysticercosis was added by WHO to the list of major neglected tropical diseases in 2010. 2- Taenia saginata the most common tapeworm in humans Disease: Taeniasis
Epidemiology
- The epidemiology of taeniasis caused by T. saginata is related to the access of cattle to human feces and to the consumption of raw or undercooked beef. - Adult worms may inhabit the intestinal tract for as long as 25 years. - The disease is endemic in Africa, South America and Eastern Europe.
Lab diagnosis:
- Identification of T. saginata Proglottids and eggs in stool. - The eggs of T. saginata and T. solium are indistinguishable; however, the two may be differentiated through examination of gravid proglottids pressed between two glass slides. If more than 13 uterine branches are present on each side of the proglottid, the infection is consistent with T. saginata.
Treatment:
- The treatment of choice is praziquantel.
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