Schistosoma mansoni infections in neonatal Biomphalaria glabrata snails.

In areas endemic for schistosomiasis, the population dynamics of the snail intermediate hosts have a direct effect on parasite transmission. The present study focused on the potential for neonatal Biomphalaria glabrata snails to become infected with Schistosoma mansoni and to produce cercariae under various conditions. It was found that snails as small as 0.74 mm in shell diameter could survive miracidial penetration and could release cercariae when as small as 1.6 mm in diameter. Cercariae produced by small snails were equally infectious for mice when compared with those shed by larger snails. Likewise, histological examination of neonatally exposed snails revealed normally developing parasites at all stages of infection. It was found that in 2 snail populations expressing either high or low susceptibility to the parasite, peak susceptibility occurred at 25 days of age in both groups. Daily cercarial production for neonatally exposed snails was initially low but increased dramatically as the snails grew, eventually reaching values as high as 2,100 cercariae/snail/day. A moderate to high percentage of snails infected as neonates was eventually capable of simultaneously producing both eggs and cercariae. These studies emphasize the potential importance of neonatal and preadult snails in helping to maintain foci of S. mansoni infection in endemic areas.