The impact of a primary infection with the incompatible digenean Plagiorchis elegans to groups composed of young, juvenile and adult Biomphalaria glabrata and a challenge infection with the compatible parasite Schistosoma mansoni was examined. Egg production of young B. glabrata was significantly reduced by P. elegans at the higher exposures of 16 eggs per snail, while egg production of adult B. glabrata was reduced at exposures of 8 and 16 eggs per snail. Egg production of juvenile B. glabrata snails was not significantly affected by any of the levels of P. elegans exposures. The survivorship of juvenile B. glabrata snails was significantly lowered by an exposure to 16 P. elegans eggs per snail. The survivorship of adult snails was significantly reduced by exposures to both 8 and 16 P. elegans eggs per snail. Interestingly enough, the survivorship of young B. glabrata snails was not significantly affected by P. elegans exposure. Snails harboring small P. elegans infections acquired a resistance to Schistosoma mansoni infection. Infection with P. elegans did not have any significant effect on the egg production of the young and adult sympatric snails, Helisoma trivolvis trivolvis. The survivorship of adult H. trivolvis trivolvis was not significantly affected by exposure to P. elegans. This being said, young H. t. trivolvis that were exposed to P. elegans had a higher survivorship than did control snails. Exposed Bulinus truncatus snails laid up to 50% fewer eggs for the first five weeks due to P. elegans infection. There was however no effect on the survivorship of the snails.

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