Field studies on the bionomics of the free-living stages of St. Lucian Schistosoma mansoni

Abstract

Densities of Schistosoma mansoni miracidia and cercariae in natural habitats in three St. Lucian valleys were monitored over a 3-year period by exposure of sentinel snails, Biomphalaria glabrata, and a cercariometric technique, supplemented by sampling of field snails. Separate measures for control of S. mansoni transmission were under evaluation in two of the valleys. Sentinel snails became infected sporadically and their infection rates per valley ranged from 0·12% to 4·99%. S. mansoni miracidial inoculation rates ranged from 1 to over 4 per infected sentinel snail. Combined rainfall of more than 3 in on the day before any day of sentinel snail exposure interfered with miracidium-snail interaction. Densities of S. mansoni cercariae ranged from 0·05 to 21 per litre of water sampled. The number of cercariae detected in a habitat by cercariometry was directly proportional to the number of infected field snails. Sentinel snail infection rates exhibited a downward and an upward trend, respectively, in the controlled and uncontrolled areas, although the changes were not significant statistically.