SUSCEPTIBILITY OF BIOMPHALARIA-GLABRATA TO INFECTION WITH ECHINOSTOMA-PARAENSEI - CORRELATION WITH THE EFFECT OF PARASITE SECRETORY-EXCRETORY PRODUCTS ON HOST HEMOCYTE SPREADING

Susceptibility of the snail Biomphalaria glabrata to infection with th e digenetic trematode Echinostoma paraensei was correlated with the ab ility of secretory-excretory products (SEP) derived from sporocysts of this parasite to interfere with the spreading behavior of host hemocy tes in an in vitro assay. In 15 separate experiments, the prevalence o f infection achieved by miracidia was positively correlated (C.C. = 0. 779, P < 0.001) with the ability of in vitro-transformed sporocysts de rived from the same batches of miracidia to produce SEP that inhibited host hemocyte spreading. Under assay conditions reflecting difference s in hemolymph volumes between juvenile snails (susceptible to infecti on) and adult snails (relatively refractory to infection), SEP had a s ignificantly greater effect on hemocytes from juvenile snails. No sign ificant differences in response to SEP were noted when equivalent numb ers of adult and juvenile hemocytes were used in the assay. Snails of the RI line strain of B. glabrata are significantly more susceptible t o infection with E. paraensei than 13-16-R1 strain snails. Exposure to SEP significantly increased the number of unspread hemocytes for both strains. However, significantly more 13-16-R1 than M line hemocytes r emained spread following SEP treatment. Echinostoma paraensei sporocys t SEP effects on host hemocyte spreading mirror observed patterns in b oth age-and strain-related susceptibility of B. glabrata to this paras ite. The results suggest that the number of hemocytes available to a p articular snail influences its vulnerability to infection with E. para ensei. (C) 1998 Academic Press.