Evaluation of an overlay technique for the recovery of Schistosoma mansoni cercariae.

The consistent recovery of schistosome cercariae from turbid water may be an important observation in the study of schistosomiasis transmission. The phototactic behaviour of cercariae was used as the basis of a technique in which cercariae were induced to migrate into a layer of clear water overlying the turbid sample; the clear layer was then filtered and the cercariae counted. The recovery rate, however, does not appear to justify the use of this technique, at least in the field.