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All representatives of tapeworms (the class, cestoda) are extremely specialized in relation to their parasitic way of life. Most species of tapeworms occur in the intestines of vertebrates, about a dozen of them- regularly in humans. What is really the cause of concern in these organisms?
Taenia saginata
This causes taeniasis saginata. Taeniasis saginata occurs worldwide but is endemic in areas of Asia, south America, and eastern Europe. It can be identified by its scolex with 4 suckers but in contrast to T.solium, no hookers. Its gravid proglottids have 17-35 primary uterine branches. Larva of T.saginata called cysticercus.
Humans are infected by eating raw undercooked beef containing larvae (fecal-oral way of transmission). In the small intestine, the larvae attach to the gut wall and take about 3 months to grow into adult worms measuring up to 10m. The gravid terminal proglottids detach, are passed in the feces, and are eaten by cattle. Embryos (oncospheres) emerge from the eggs in the cow's intestine and burrow into a blood vessel, where they are carried to skeletal muscle. They develop into cysticerci in the muscle. The cycle is completed when the cysticerci are ingested. Humans are the definitive hosts, and cattle the intermediate hosts.
Clinical manifestation of taeniasis saginata are: abdominal pain, nausea, diarrhea, weight loss and infection may be asymptomatic. In some, proglottids appear in stools and may even protrude from the anus. Laboratory diagnosis is based on the determination of the gravid proglottids (with 17-35 uterine branches) found in stools.Mebendazole is also used as the treatment therapy to cure taeniasis saginata. Prevention of taeniasis saginata involves cooking beef adequately and preventing cattle from ingesting human feces by disposing of waste properly.
Diphyllobothrium latum
The fish tapeworm causes diphyllobothriasis. This disease is found worldwide but is endemic in areas where eating raw fish is the custom, such as Scandinavia, northern Russia, Japan, Canada, USA (northern Michigan, Minnesota).
Diphyllobothrium latum can be identified by its scolex with 2 elongated sucking grooves by which the worm attaches to the intestinal wall. The proglottids are wider than they are long, and the gravid uterus is in the form of a rosette. Adult D.latum is the longest of the tapeworms, measuring up to 13m. Larva of D.latum called plerocercoid.
Humans are infected by eating raw or undercooked fish containing larvae (fecal-oral way of transmission). In the small intestine, the larvae attach to the gut wall and develop into adult worms. Gravid proglottids release fertilized eggs, and the eggs are then passed in the stools. The immature eggs must be deposited in fresh water for the life cycle to continue. The embryos emerge from the eggs and are eaten by tiny copepod crustacea (first intermediate hosts). There, the embryos differentiate and form procercoid larvae in the body cavity. When the copepod is eaten by freshwater fish, eg, pike, trout, and perch, the larvae differentiate into plerocercoids in the muscle of the fish (second intermediate host). The cycle is compelled when raw or undercooked fish is eaten by humans (definitive hosts).
Infection by D.Latum causes little damage in the small intestine. In some individuals, megaloblastic anemia occurs as a result of vitamin B12 deficiency caused by preferential uptake of the vitamin by the worm. Most patients are symptomatic, but abdominal discomfort and diarrhea can occur. Diagnosis depends on finding the typical eggs, oval, yellow-brown eggs with an operculum (lid-like opening) at one end, in the stools.
Praziquantel anti- parasitic drug is the best choice of treatment therapy and prevention involves adequate cooking of fish and proper disposal of human feces.
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