The effects of parasite dose, host size and method of exposure on the reproductive capacity and survival of Biomphalaria glabrata infected with the incompatible digenean, Plagiorchis elegans

The digenean parasite, Plagiorchis elegans can establish infections in the incompatible snail, Biomphalaria glabrata , a vector of human schistosomiasis. Although embryonic development is arrested at the sporocyst stage, infection with a single parasite egg reduced reproductive success of this incompatible host to 64%. Heavier doses reduced this to 45%. Biomphalaria glabrata quickly acquired large numbers of parasites by ad libitum browsing on egg-contaminated substrates. Age of the host at exposure affected subsequent reproductive success and survival. Snails exposed as young (3mm), produced 54% fewer eggs, and suffered relatively high mortality. Adults (9mm) were affected only marginally. Plagiorchis elegans shares its ability to establish truncated infections in incompatible hosts with at least one other plagiorchiid. Haematoloechus medioplexus castrated the snail Stagnicola elodes, but not B. glabrata. Findings are discussed in the context of using incompatible digenean parasites as agents in the biological control of snails and snail-borne diseases, and ecological consequences of these infections.