Diphyllobothrium latum and related species (the fish or broad tapeworm), the largest tapeworms that can infect people, can grow up to 30 feet long. While most infections are asymptomatic, complications include intestinal obstruction and gall bladder disease caused by migration of proglottids. Diagnosis is made by identification of eggs or segments of the tapeworm in a stool sample with a microscope. Safe and effective medications are available to treat Diphyllobothrium. Infections are acquired by eating raw or undercooked fish, usually from the Northern Hemisphere (Europe, newly independent states of the Former Soviet Union, North America, Asia), but cases have also  been reported in Uganda and Chile. Fish infected with Diphyllobothrium larvae may be transported to and consumed in any area of the world. Adequately freezing or cooking fish will kill the parasite.

Image: L: Section of an adult D. latum containing many proglottids. The scolex was not present in this specimen. Scale is in centimeters. R: Scolex of D. latum. Credit: Florida State Public Health Laboratory, DPDx