The Great Lakes have many kinds of freshwater fishes and the cities around the lake have many people who eat those fish. Years ago people became infected with tapeworms from tasting a mixture of raw fish prior to cooking. The human intestines were found to be perfectly satisfactory to these tapeworms. As a matter of fact some tapeworms that infected humans were found to be many yards long. And to make matters worse at one time there was a company that package the tapeworm larvae in capsules and sold them as weight-reducing medicine.
Some experts feel that most adult tapeworms do no harm.
A healthy host provides food and shelter for healthy tape worms. Should the host starve or become stressed, tapeworms are usually the first casualties, expelled from the got by the host's own defenses. The idea that tapeworms cause a host to lose weight is incorrect, unless the host is abnormal, rather then the usual host for that worms species. Larval tapeworms, on the other hand, can cause damage by their very numbers and locations, and because they are buried in tissues from which they cannot escape. Fish may acquire tapeworm infections by consuming infected tubifex worms.