Meeting Abstract
Avian schistosomes are snail-borne trematode parasites (Trichobilharzia spp.) that can cause a nasty skin rash in humans when their cercariae mistake us for their normal bird hosts. The aim of this study was to investigate the spatial drivers of Trichobilharzia spp. cercaria abundance throughout Northern Michigan inland lakes. For 38 sites on 16 lakes, we measured and assessed several dozen potential environmental predictors that we hypothesized might drive overall cercaria abundance, including local densities of intermediate and definitive hosts, temperature, water chemistry parameters, water clarity and growth rates of algal periphyton (snail food), physical characteristics of each lake and local site, zebra mussel (Dreissena spp.) abundance, and local abundance of predatory crayfish. We also measured daily abundance of schistosome cercariae in the water over a 5-week period, with support from local citizen scientists who collected and preserved filtered water samples for later qPCR analysis. The best and highly significant predictor of cercaria abundance was host Stagnicola spp. snail density, suggesting that intermediate host abundance is the primary driver of avian schistosome abundance in these lakes. We also found a significant negative relationship between cercaria abundance and submerged aquatic vegetation, possibly due to direct negative effects of vegetation on cercaria survival or movement (i.e., influx from deep-water offshore snail beds). If these effects are found to be causal, then managing the abundance or types of vegetation in the riparian zone could provide new tools for reducing swimmer’s itch risk in northern MI lakes.
