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Diphyllobothriasis (Fish Tapeworm Infection)

By

Chelsea Marie

, PhD, University of Virginia;


William A. Petri, Jr

, MD, PhD, University of Virginia School of Medicine

Reviewed/Revised Nov 2023
View PATIENT EDUCATION

Diphyllobothriasis is infection with intestinal tapeworms of the family Diphyllobothriidae. They are acquired by eating raw or undercooked freshwater fish. Treatment is with praziquantel or niclosamide.

D. latum is the most common and among the largest parasites that infect humans (up to 10 m in length). D. latum and other Diphyllobothriidae species have aquatic life cycles. In freshwater, eggs of D. latum from human feces hatch into free-swimming larvae, which are ingested by microcrustaceans. The microcrustaceans are ingested by fish, in which the larvae become infective. Several other Dibothriocephalus species and Adenocephalus pacificus can infect humans after ingestion of raw fish, but they are not as common.

Diphyllobothriasis occurs worldwide, especially where cool lakes are contaminated by sewage. Infections in the United States and northern Europe occur in people who eat raw or undercooked freshwater fish. Infection is less common with current sewage treatment.

Symptoms and Signs of Diphyllobothriasis

Diagnosis of Diphyllobothriasis

  • Microscopic examination of stool for ova and proglottids

  • Complete blood count

Diagnosis of diphyllobothriasis is by identification of characteristic operculated eggs or broad proglottids in stool. Complete blood count is done to check for megaloblastic anemia.

Treatment of Diphyllobothriasis

  • Praziquantel

  • Alternatively, niclosamide (outside of the United States)

Treatment of diphyllobothriasis is with a single oral dose of praziquantel (1 Treatment reference Diphyllobothriasis is infection with intestinal tapeworms of the family Diphyllobothriidae. They are acquired by eating raw or undercooked freshwater fish. Treatment is with praziquantel or... read more ). Alternatively, a single dose of niclosamide (unavailable in the United States) is given. A stool sample should be repeated one month after therapy is completed to verify cure.

Vitamin B12 may be needed to correct megaloblastic anemia if present.

Treatment reference

  • 1. Braseth AL, Elliott DE, Ince MN: Parasitic Infections of the Gastrointestinal Track and Liver. Gastroenterol Clin North Am 50(2):361-381. 2021. doi:10.1016/j.gtc.2021.02.011

Prevention of Diphyllobothriasis

Prevention of diphyllobothriasis is by thoroughly cooking freshwater fish (internal temperature of ≥ 63° C [≥ 145° F]) or freezing it at recommended temperatures can kill fish tapeworms. For freezing, recommendations include the following:

  • Freezing at -20° C (-4° F) or below for 7 days (total time)

  • Freezing at -35° C (-31° F) or below until solid and storing at -35° C (-31° F) or below for 15 hours

  • Freezing at -35° C (-31° F) or below until solid and storing at -20° C (-4° F ) or below for 24 hours

Drugs Mentioned In This Article

Drug Name Select Trade
Biltricide
View PATIENT EDUCATION
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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