Physiologic studies of snail-schistosome interactions and potential for improvement of in vitro culture of schistosomes.

Despite extensive efforts to develop suitable media for rearing the intramolluscan stages of schistosomes, successful in vitro culture of these parasites remains elusive. Recent 31P NMR studies demonstrated that the levels of free phospholipids, particularly phosphatidylcholine, in the digestive gland of the snail, Biomphalaria glabrata, were dramatically reduced when the host was infected with Schistosoma mansoni. It was speculated that absorption of host phosphatides may be an important source of membrane phospholipid precursors and fatty acids for developing sporocysts and cercariae. During the present investigations, B. glabrata was maintained on a high fat diet of egg yolk, and the lipid composition of control uninfected and infected snails examined by 31P and 13C NMR. In addition, the levels of host hemolymph metabolites, including glucose and urea, considered as indicators of parasite nutrient uptake, were monitored. The lipid level of snails fed egg yolk was greatly increased, and hosts developed patient infections in approximately half the time of infected snails maintained on lettuce. The composition of the free phospholipids accumulated in the tissues of B. glabrata fed egg yolk were the same as those previously reported in the cercarial stage of S. mansoni. Moreover, the fatty acids of S. mansoni and those reported here in the neutral lipids and free phosphatides in the host tissues were similar. Uninfected snails maintained on lettuce had higher hemolymph levels of glucose than those reared on egg yolk, and infected hosts on egg yolk had significantly lower levels of hemolymph urea. Beta-hydroxybutyrate was the principal hemolymph metabolite in snails fed egg yolk, but was not detected in snails maintained on lettuce.(ABSTRACT TRUNCATED AT 250 WORDS)