Buy the Book PDA Download

Update Me E-mail alerts The Merck Manual Minute

Print This Topic Email This Topic

Diphyllobothriasis is infection with the freshwater fish intestinal tapeworm, Diphyllobothrium latum. Treatment is with praziquantel.

D. latum is the largest parasite of humans (up to 10 m in length). It and Sparganum mansoni are the only human tapeworms with aquatic life cycles. In freshwater, eggs of D. latum from human feces hatch free-swimming larvae, which are ingested by microcrustaceans that are themselves ingested by fish, in which the larvae become infective. Diphyllobothriasis occurs worldwide, especially where cool lakes are contaminated by sewage. Infections in the US and northern Europe occur in people who eat raw freshwater fish. Infection is less common with current sewage treatment.

Infection is usually asymptomatic, but mild GI symptoms may be noted. Fish tapeworms take up dietary vitamin B₁₂, which occasionally results in B₁₂ deficiency and megaloblastic anemia. Diagnosis is by identification of characteristic operculated eggs or broad proglottids in the stool.

Treatment is with a single oral dose of praziquantel Some Trade Names
BILTRICIDE
Click for Drug Monograph
, 5 to 10 mg/kg. Vitamin B₁₂ may be needed to correct the anemia. Thorough cooking of freshwater fish or freezing at −10° C (14° F) for 48 h prevents infection.

Last full review/revision November 2005

Content last modified November 2005