Diphyllobothrium latum, or the fish tapeworm, is basically a Scandinavian import to the United States. As Robert Desowitz describes in his classic book “New Guinea Tapeworms and Jewish Grandmothers“, many Scandinavian fishermen settled in the cool lake regions of Minnesota and Wisconsin in the nineteenth century and continued to fish for a living but with that brought them the habit of defecating in the water.

This in turn infected the fish of these lakes with the parasite they brought with them.

So how did this affect Jewish grandmothers? The fish from the upper Midwest would be imported to New York City. Pike, carp and pickerel would be available to the main customers, Jewish grandmothers who would create balls of minced fish called gefilte fish.

Diphyllobothrium latum life cycle/CDC
Diphyllobothrium latum life cycle/CDC

The gefilte fish would be boiled until it was done. This issue for the Jewish grandmothers is they would use their instincts on determining when it was done. They did this by tasting the fish at different stages of cooking and as Dr. Desowitz cleverly states, “they unwittingly get a Scandinavian immigrant in their digestive tract”.

What is the fish tapeworm? It is several species from the genus Diphyllobothrium with D. latum being most common. The adult tapeworm can grow in excess of 50 feet in length.

It occurs in lake regions in the northern hemisphere but cases are seen in the sub-arctic, temperate and tropical zones where eating raw or partly cooked fish is popular.

In the U.S., infections are sporadic and usually come from eating uncooked fish from Alaska or, less commonly, from Midwestern and Canadian lakes.

The disease is frequently asymptomatic, however some people develop vitamin B12 deficiency (pernicious) anemia. Very heavy infections may cause diarrhea, obstruction of the bile duct or intestine and toxic symptoms.

Humans and other animals infected with this tapeworm can disseminate eggs into the environment for many years as long as worms remain in the intestine.

Diagnosis is by identification of the characteristic eggs in feces. Treatment with the antiparasitic drug Praziquantel is the treatment of choice.

Prevention of this disease is by thorough cooking of freshwater fish.

Fortunately for the Jewish grandmothers, the introduction of fish inspection, sanitary practices and thermometers (which was considered high tech back then), this tapeworm is relatively rare in the U.S.