Tapeworm Infection, Fish

Essentials of Diagnosis

• Infections are generally asymptomatic

• Nonspecific gastrointestinal symptoms, including diarrhea, may occur

• Prolonged heavy infection can lead to megaloblastic anemia and neuropathy from vitamin B₁₂ deficiency

General Considerations

• Six tapeworms infect humans frequently

• The large tapeworms are

  • Taenia saginata (the beef tapeworm, up to 25 m in length)

  • Taenia solium (the pork tapeworm, 7 m)

  • Diphyllobothrium latum (the fish tapeworm, 10 m)

• The small tapeworms are

  • Hymenolepis nana (the dwarf tapeworm, 25–40 mm)

  • Hymenolepis diminuta (the rodent tapeworm, 20–60 cm)

  • Dipylidium caninum (the dog tapeworm, 10–70 cm)

• Eggs passed in human feces that reach fresh water are taken up first by crustaceans, which in turn are eaten by fish, both of which are intermediate hosts

• Human infection results from eating undercooked freshwater fish

• Infection with multiple worms over many years can occur

• Nonhuman reservoir hosts include dogs, bears, and other fish-eating mammals

Demographics

• D latum is found in temperate regions

Symptoms and Signs

• Large tapeworm infections are generally asymptomatic

• Nonspecific gastrointestinal symptoms (eg, diarrhea)

• Megaloblastic anemia and neuropathy can result from prolonged heavy infection

Differential Diagnosis

• Beef, pork, dwarf, rodent, or dog tapeworm

• Chronic fatigue syndrome

• Chronic hepatitis

• Irritable bowel syndrome

• Amebiasis

• Ascariasis

• Enterobiasis (pinworm, mostly children)

• Hookworm disease

• Strongyloidiasis

• Celiac disease or tropical sprue

• Pernicious anemia (D latum)

• Diagnosis is usually made based on the identification of characteristic eggs or proglottids in stool

• Egg release may be irregular, so examination of multiple specimens or concentration techniques may be needed

Medications

• Praziquantel

  • Treatment of choice

  • Single dose of 5–10 mg/kg is highly effective

  • Side effects include headache, malaise, dizziness, abdominal pain, nausea

• Niclosamide

  • Alternative therapy

  • Single dose (2 g for adults chewed) is effective

  • Side effects include nausea, malaise, abdominal pain

Follow-Up

• A disintegrating worm is usually passed within 24–48 h of treatment. Since efforts are not generally made to recover and identify the scolex, cure can be presumed only if regenerated segments have not reappeared 3–5 months later

• If it is preferred that parasitic cure be established immediately, the head (scolex) must be found in posttreatment stools; a laxative is given 2 h after treatment, and stools must be collected in a preservative for 24 h. To facilitate examination, toilet paper must be disposed of separately

When to Refer

• If confirmation of the diagnosis is needed or if symptoms are progressive despite therapy

• If there is difficulty distinguishing tapeworm-induced B₁₂ deficiency from pernicious anemia