Veterinary Epidemiology and Zoonosis

DIPHYLLOBOTHRIOSIS

Synonym

• Fish tapeworm infection, Pernicious anaemia

Type of zoonosis

• Non-obligatory cyclozoonosis, Fish-borne zoonosis

Definition

• It is a fish-borne and non-obligatory cyclozoonosis, caused by Diphyllobothrium latum. The condition is usually asymptomatic. In some patients, it develops pernicious anaemia (macrocytic hypochromic anaemia due to vitamin B12 deficiency) due to competition between host and parasite for vitamin B12.

Etiology

• It is caused by fish tape worm, Diphyllobothrium latum.
• There are two intermediate hosts involved to complete its life cycle, includes plankton crustacean and freshwater fish.

Reservoir and mode of transmission

• D.latum is common in northern temperate regions where the fish are eaten raw (e.g., in the Baltic countries, Finland and Canada / Alaska) America, especially Peru.
• Humans, dogs and cats are definitive hosts for D.latum.
• Two intermediate hosts such as plankton crustacean and freshwater fish to complete its life cycle.
• Gravid proglottids are passed in the faeces of the definitive host, and eggs hatch in water.
• Hatched out eggs infect the plankton crustacean (first intermediate hosts), then freshwater fish consume these first intermediate hosts), and the larvae encysted in the musculature.
• Humans get parasitised by eating raw infected fish.

Disease in animals

• Usually no clinical infection is seen in dogs and cats, but heavy infection with larvae of D.latum can kill the second intermediate hosts (fishes).

Disease in humans

• Incubation period is 3 to 6 weeks from ingestion to adult D.latum.
• The condition is usually asymptomatic. In some patients, it develops pernicious anaemia (macrocytic hypochromic anaemia due to vitamin B12 deficiency) due to competition between host and parasite for vitamin B12.
• The presence of the large tapeworm in the intestine can cause mechanical obstruction.
• Megaloblastic anaemia occurs owing to vitamin B12 deficiency.

Diagnosis

• Faecal examination for detection of eggs.

Treatment

• Anthelmintics, especially niclosamide and praziquantel can be given to human beings.

Prevention and control

• Freezing or salt curing of fish destroys D.latum.
• Cooking of fish destroys this parasite.
• Avoid eating raw or under cooked infected fish.
• Dispose human faeces hygienically.