Largest parasite

The broad or fish tapeworm Diphyllobothrium latum, inhabiting the small intestine of fishes and sometimes humans too, attains a length of 9.1–12.1 m (30–40 ft) but can exceptionally reach 18.28 m (60 ft). It has been estimated that if a specimen survived for ten years, it could possess a chain of segments (proglottids) measuring almost 8 km (5 miles) long and containing 2,000 million eggs! Another human parasite, the pork tapeworm Taenia solium, sometimes exceeds 6.09 m (20 ft); and the beef tapeworm Taeniarhynchus saginatus can reach up to 15.24 m (50 ft). One extreme Taeniarhynchus specimen measured over 22.86 m (75 ft) – i.e. three times as long as the entire human intestine! Many "fish eating" vertebrates can serve as the definitive host for Diphyllobothrium latum (the broadfish tapeworm), including humans, dogs, foxes, cats, mink, bears and seals. The adult tapeworm lives in the host's small intestine, and in humans the tapeworm can reach a length of 10 m (30 ft) and produce over a million eggs a day! The life cycle of the tapeworm involves two intermediate hosts. The first intermediate host is a copepod, the second intermediate host is a fish, often pike or salmon, and the definitive host is infected by eating raw or undercooked fish. In humans the tapeworm is more prevalent in areas where humans eat lots of fish; this includes Scandinavia and areas bordering the Great Lakes in the USA. Dogs and cats are often infected when they are fed the offal remaining after cleaning fish.