Biological control of the snail intermediate hosts of Schistosoma mansoni in Martinique, French West Indies.

In Martinique water-cress beds constituted the last transmission sites for schistosomiasis. The competitor snail, Melanoides tuberculata, was introduced at the beginning of 1983 to a group of water-cress beds and eliminated the snail hosts, Biomphalaria glabrata and B. straminea, in less than two years. Following this first success, M. tuberculata was introduced to the other groups of beds which were inventoried at the beginning of the eighties. At the present time, B. glabrata and B. straminea have totally disappeared from eight sites and only a few individuals have been recorded from 12 sites. The two remaining water-cress beds have dried up and were abandoned.

Biological control of Biomphalaria glabrata and B. straminea by the competitor snail Thiara tuberculata in a transmission site of schistosomiasis in Martinique, French West Indies.

In Martinique, intestinal schistosomiasis was discovered at the beginning of this century. The intermediate host snail, Biomphalaria glabrata, was considered in the past as a common species in the different habitats of the island, but during the last decade it has been found only in water-cress beds. Several of these water-cress cultures contained mixed populations of B. glabrata and B. straminea. Moreover, these habitats also constituted transmission sites for Schistosoma mansoni infection. In 1979 the thiarid snail Thiara ( = Melanoides) tuberculata was discovered in Madame river, Fort-de-France, and in the following years at other sites. In 1983 a programme of biological control using this snail was started in two groups of water-cress beds. In 1981-1982 the study site, Roxelane valley, sheltered important populations of B. glabrata (45-256 individuals/m2) and of B. straminea (2-30 ind./m2). In January 1983 the competitor T. tuberculata was introduced into the two groups of water-cress beds (1.3 and 1.7 ind./m2 respectively) and during subsequent years snail population sampling was carried out. The results showed rapid colonization by the competitor snail, whose densities reached 178 and 325 ind./m2 in November 1983 and a maximum of 9941 and 13,388 ind./m2 in October 1984. During that time, B. glabrata populations declined: 153 and 41 ind./m2 in November 1983, 4 and 0 ind./m2 in October 1984, and 0 ind./m2 in the two groups of water-cress beds in October 1985. A similar phenomenon was observed for B. straminea. Since October 1985 neither planorbid species has been found by exhaustive sampling of the habitats.(ABSTRACT TRUNCATED AT 250 WORDS)

[Activities of a Schistosoma mansoni focus of transmission in Martinique (French Antilles)]. / Le fonctionnement d'un site de transmission à Schistosoma mansoni en Martinique (Antilles Françaises).

A focus of intestinal schistosomiasis was discovered in november 1981 in Martinique in the Saint-Pierre area. An analysis of its structure and of the mecanisms of the transmission of the parasite was carried out between 1981 and 1983. This focus presents the following particularities: a transmission site very small constituted by water cress beds; a small human population infected with a prevalence of 13% (positive stools) to 41,3% (positive serologies); a weak fecal contamination of the water; a non functioning sewage stabilization tank is responsible for this contamination; a rich population of the snail host Biomphalaria glabrata (40,5 to 256,3 Bg/m2) with a low prevalence of infestation (0,13 to 0,59%); low cercarial densities in the water cress bed waters; a very low contamination of the Roxelane river water in to which the water from the water cress beds flows. The epidemiological importance of this contamination has proved very low but not altogether absent. This focus appears as a particular case in Martinique because all the surveys which have been conducted in the island to date has not uncovered a similar example.

[Freshwater snails and vectors of schistosomiasis mansoni in Martinique (French West Indies)]. / Faune malacologique dulaquicole et vecteurs de la Schistosomose intestinale en Martinique (Antilles Françaises)

An inventory of the freshwater Molluscs in Martinique was worked out during 1972 to 1978. Each of the 19 species is shown with its main characteristics. The distribution of Biomphalaria glabrata and Biompharia straminea was studied. The epidemiological importance of these two snails is discussed.