Cestode Zoonoses - DIPHYLLOBOTHRIASIS

(Fish tapeworm infection) A benign tapeworm infection of the small intestines caused by eating raw fish. The causative agents are Diphyllobothrium latum and D. pacificum (Cestoda). There is no vaccine. D. latum is common in northern temperate regions where the fish are eaten raw (e.g., in the Baltic countries, Finland and Canada/Alaska). D. pacificum is common in coastal South America, especially Peru.

RESERVOIR AND MODE OF TRANSMISSION:

The definitive hosts of D. latum include humans, dogs and cats. For D. pacificum the natural reservoir is seals. Two intermediate hosts include a plankton crustacean and a freshwater fish. Gravid proglottids pass in the feces of the definitive host. The eggs hatch in lakes and waterways and then infect the crustacean. Freshwater fish consume these and the larvae encyst in the musculature. The fish, in their turn, may be eaten by larger fish which can still transmit the infection. Humans acquire the parasite by eating raw infected fish.

INCUBATION PERIOD:

Humans. 3-6 weeks from ingestion to adult tapeworm. Animals. Unknown but presumably as for humans, in dogs and cats.

CLINICAL FEATURES:

Humans. The condition is usually asymptomatic. Some patients develop vitamin B12 deficiency anemia. Massive infection may cause diarrhea and intestinal obstruction. Animals. No clinical signs are seen in dogs and cats. Heavy infection with larvae can kill the fish intermediate host.

PATHOLOGY:

Humans. The presence of the large tapeworm, 3 to 10 meters long, in the intestine can cause mechanical obstruction. Megaloblastic anemia occurs owing to vitamin B12 deficiency. Animals. Subclinical. In fish, myositis and possibly even death occur in heavy infestation.

DIAGNOSIS:

Humans and animals. Identify characteristic eggs in feces.

PROGNOSIS:

Humans. Usually benign. Animals. Usually benign, but heavy infection may be fatal to fish.

PREVENTION:

Humans and animals. Dispose of feces hygienically. Educate for proper cooking of fish. Freeze fish or salt cure before marketing.

TREATMENT:

Humans and animals. Anthelmintics, especially niclosamide and praziquantel.

LEGISLATION:

Humans and animals. None.