Investigation of the Ecological Origins of Schistosome Cercarial Dermatitis, with Emphasis on the Intermediate Snail Hosts of Schistosomatidae Trematodes, at Higgins Lake in Roscommon County, Michigan
Nyman, Patrick M.
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The biologist Cort discovered the relationship between nonhuman schistosomes and the skin ailment known as schistosome cercarial dermatitis in 1928 at the University of Michigan Biological Station. These digenetic trematodes cause an allergic sensitization reaction in people who come into contact with the cercarial stage in lakes throughout the United States. The parasites cycle between a definitive host, including waterfowl and some mammals, and an intennediate aquatic snail host. The objective of this study was to explore the ecological root of schistosome cercarial dennatitis at Higgins Lake in Roscommon County, Michigan. The focus was the acquisition of information regarding the intermediate hosts in the lake. New potential hosts were identified and previously known hosts were examined for incidences of infection. Seven species of snails were encountered that belong to three families known to host nonhuman schistosomes, two of which were proven to harbor the parasite. Distribution of both Stagnicola emarginata (Say) and Physella (Costatella) integra integra morph walkeri (Crandall), with an emphasis on geographic dispersal, depth ranges, densities at different locations, and shell length, was analyzed with relation to schistosome infection. Both species were found at numerous locations. P. integra was found associated only with shallow depths less than 0.6 meters, while S. emarginata was found at all depths explored, 0.3 to 0.9 meters. Larger shell lengths in S. emarginata had higher incidences of infection than did those with shorter shells.