Causative agent of diphyllobothriosis
Occurrence, morphology, and life cycle. This tapeworm is endemic in lake regions in Europe (above all in Russia, less frequently in Scandinavia, Germany, Switzerland, Italy, etc.), Asia, and America and parasitizes in the small
intestine of humans and fish-eating mammals such as pigs, dogs, and cats. The parasite has two elongated grooves (bothria) on its head, it is 2-15 m long with numerous (up to 4000) proglottids (Fig. 10.7a, b, p. 561). The oval, yellow-brown, operculated eggs (approx. 70 x 50 im) are similar to those of trematodes (Fig. 10.1, p. 544). The life cycle includes copepods as primary and freshwater fish as secondary intermediate hosts. Humans acquire the infection when eating raw or undercooked fish containing infective stages (plerocercoids) of the tapeworm. Development of a sexually mature tapeworm can be completed within 18 days.
Clinical manifestations The course of a Diphyllobothrium infection is often devoid of clinical symptoms, with only mild gastrointestinal distress in some cases. Anemia and other symptoms due to vitamin B12 uptake by the parasite is observed in about 2 % of tapeworm carriers.
Diagnosis, therapy, and prevention. Diagnosis is made by detection of eggs in stool, sometimes proglottids are excreted. Praziquantel is a suitable drug for therapy. Preventive measures include wastewater hygiene and not eating undercooked fish. The plerocercoids can be killed by boiling or deep-freezing (24 hours at -18 °C or 72 hours at -10 °C).
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