Infestation of fish tapeworm Diphyllobothrium latum is the result of ingesting raw freshwater fish and occurs worldwide. The infection usually produces a single worm and is generally without symptoms, but it may cause vague intestinal discomfort. Pernicious anaemia can develop as a result of the worm's vitamin B-12 absorption. Diagnosis is made by finding eggs in human faeces.
Fish tapeworm is is especially common in Scandinavia and the Far East.