RESUMO
This study assessed the effect of association between the oligochaete Chaetogaster limnaei and the snail Biomphalaria alexandrina on schistosomiasis transmission in aquatic habitats. This experimental study included factors affecting the oligochaete / snail association such as water volume and snail species and size. The effect of Chaetogaster on snail survivorship, growth and reproduction, life of the free - living larval stages of Schistosorna mansoni and on infection of the snail with miracidia were also studied. Results show that there was a positive correlation between snail size and infestation intensity of the oligochaete. The infestation of B. alexandrina by Chaetogaster had no effect on the survival and growth of snails, but led to a remarkable reduction in egg production. Chaetogaszer proved to have predatory activity on S. mansoni miracidia and cercariae and the number of predated organisms increased with the increase of prey density. Introducing one Chaetogaster per snail after exposure to S. mansoni miracidia showed no effect on infection rate of snails and length of incubation and shedding periods but reduced significantly the total periodic cercarial production of the parasite. This study gives indication that Chaetogaster may play a significant role in reducing the population of the medically important snail B. alexandrina via suppressing its productivity, as well as reducing schistosome transmission