Ecological factors in schistosome transmission, and an environmentally benign method for controlling snails in a recreational lake with a record of schistosome dermatitis

The avian schistosomes, Trichobilharzia stagnicolae, T. physellae and Gigantobilharzia sp., that cause Schistosome Dermatitis (Swimmers' Itch) in humans were studied in the laboratory and at Cultus Lake, British Columbia, Canada in relation to the biology and behavior of their intermediate snail hosts, Stagnicola catascopium, Physa sp. and Gyraulus parvus, respectively, and their definite bird hosts. Wind-driven, surface currents were measured. Populations of snails, close to host-bird roosting logs had a very high prevalence of schistosome infections. An experiment that mechanically disturbed the epilithic habitat of the snails using a boat-mounted rototiller or a tractor and rake, eliminated almost all of the snails if the disturbance was done in areas of high snail concentration in shallow areas of the lake during the breeding and early development phase of the snail. It is proposed that the incorporation of snail habitat disturbance into management programs is an effective way to control Schistosome Dermatitis.