Two human cases of tapeworm have been reported to the Missoula City-County Health Department in the past two months. Tapeworms are parasites and this particular one -- D. latum also known as the fish tapeworm -- is rarely diagnosed in the US.
Humans can get this tapeworm only by eating raw or undercooked freshwater fish or fish that has been in fresh water at some point. This tapeworm is NOT spread from person to person or from household pets or any animal other than freshwater fish.
The only 100% effective way to prevent infection with D. latum is to consume NO freshwater fish (salmon or trout) in a raw or undercooked state. The “raw” fish served as sushi is required by food safety regulations to have gone through a parasite killing phase that involves freezing it at low temperatures for prescribed periods of time, but there remains some risk in consuming it.
The Missoula City-County Health Department conducted extra inspections of all the licensed food establishments in Missoula County that sell freshwater fish. Product that was not documented as having been through the parasite-killing freeze step was removed from sale by February 27th. Fish served before that date may have been infected.
Most humans infected with D. latum tapeworm have no symptoms. Those that do
develop symptoms or signs may have:
Tapeworm infection is readily treatable with a prescription medication. Diagnosis will probably require checking stool samples for the parasite and its eggs.
Diagnosis and treatment must be made by a licensed medical provider who can prescribe. For related questions on fish preparation, prevention, and assistance in finding a health care provider if you do not have one, please call the Missoula City-County Health Dept. at 258-3896.