Biological control of the snail hosts of Schistosoma mansoni in the Caribbean area using Thiara spp.

Field observations and experiments using thiarid snails as competitors of Biomphalaria spp., potential intermediate hosts of Schistosoma mansoni in the Caribbean area, are reviewed. The parthenogenetic snails, Thiara granifera and T. (= Melanoides) tuberculata, were introduced to the Neotropical area in recent decades. In numerous islands and countries, these oriental species have demonstrated their capacity to colonize rapidly and densely many types of habitats while at the same time reducing and even eliminating populations of Biomphalaria spp. The results of field experiments, carried out in several Caribbean islands, have shown the efficiency as well as the limitations of T. tuberculata as a competitor of B. glabrata and B. straminea. In St. Lucia, B. glabrata was apparently eliminated from marshes and streams, 6 to 22 months after the introduction of the competitor. In Martinique, T. tuberculata was introduced into two groups of water-cress beds which constituted the last transmission sites of schistosomiasis on the island. In just less than three years after the introduction of the competitor, both B. glabrata and B. straminea have been eliminated from the transmission sites. In Guadeloupe, several introductions have been carried out in different types of habitat such as permanent ponds, canals, streams and temporary marshes. The findings of all field experiments have indicated that thiarid snails as competitors of pulmonates are favoured by the presence of permanent and stable habitats, preferably shallow, with emergent plants and well oxygenated. On the other hand, the competitor snails are at a disadvantage in waterbodies which are temporary, extremely deep, poorly oxygenated or with a dense mat of floating aquatic vegetation.(ABSTRACT TRUNCATED AT 250 WORDS)