[Repopulation of breeding habitats of Biomphalaria glabrata after treatment with niclosamide].

Experiments were undertaken both in the laboratory and in the field between 1980-1984 to evaluate the causes of repopulation of breeding places of Biomphalaria glabrata following treatment with Niclosamide. Laboratory bioassays showed that the susceptibility to emulsifiable Niclosamide of B. glabrata collected monthly from an irrigation ditch system varied during the year. Lethal concentrations (LC90) ranged between 0.15 mg/l-1 and 0.60 mg/l-1. Statistically significant differences (alpha = 0.01) were evident between the months of May/82 and January/83 and December/82 and January/83, and were related to snail nutrition. In the field two types of foci of B. glabrata were treated with 10 ppm of Niclosamide. The first one consisted of a reservoir of 12000 1 of water in which 14.5% of snails were infected with Schistosoma mansoni. One application of molluscicide followed by cleaning of the reservoir eliminated all the snails. The second one consisted of an irrigation system in which 5.6% of the snails were infected with S. mansoni. One application of molluscicide without cleaning the ditches reduced the density of snails by 98%. The causes of the survival of 2.0% of the snails in the ditches are discussed in relation to the substratum of the breeding places and the treatment technique.