Displacement of Biomphalaria glabrata by the snail Thiara granifera in field habitats in St. Lucia, West Indies.

Thiara granifera is a melaniid snail capable of maintaining very high densities in a variety of habitats. It has been introduced into the New World from the Far East and is now spreading rapidly throughout the Caribbean. In Puerto Rico and Dominica casual observations following natural invasion by T. granifera suggest that it may exert a powerful restraining influence on populations of Biomphalaria glabrata, the major intermediate host of Schistosoma mansoni in the Caribbean. The potential of T. granifera in biological control is being investigated in St. Lucia. In four field trials, B. glabrata was apparently eliminated from marshes and streams six to 22 months after the introduction of T. granifera. Thiara granifera shows promise as a major factor in the suppression of schistosomiasis in the Caribbean, but it is unsuitable for universal use as it is an intermediate host of the lung fluke, Paragonimus westermani.

Reduction in transmission of Schistosoma mansoni by a four-year focal mollusciciding programme against Biomphalaria glabrata in Saint Lucia.

The effect of transmission of Schistosoma mansoni of a focal snail control programme was investigated over four years amongst approximately 1250 people living in five communities in the steep-sided Soufriere river valley, St. Lucia, West Indies. Bayer 6076 was applied from constant flow drip cans to 12 stream sections at a target dose of 8 mg/litre clonitralide every four weeks. Only proven and potential transmission sites were treated; marsh habitats, where Biomphalaria glabrata were widespread, were ignored. In the stream snail numbers were reduced by 94% in the first year and by 100% thereafter. Incidence of new S. mansoni infections amongst children fell from 18% in the last year before control to 6% and 9% after three and four years respectively. Amongst children and adults in the four years of control the conversion/reversion ratio declined leading to a lowering of the over-all prevalence from 40% to 22%. Parasitologically the results were similar to those of a previously evaluated area-wide mollusciciding programme. The mean annual cost per person protected was US $2.60. This figure is atypically high because the topography of the area severely limited the population size.

La esquistosomiasis y sus huespedes intermediarios en las Pequenas Antillas. / Schistosomiasis and its intermediate hosts in Lesser Antillean Islands

La esquistosomiasis representa una amenaza importante para la salud en la region del Caribe. Este articulo analiza la situacion en relacion con esta enfermedad y diversos factores que contribuyen a su transmision en las Pequenas Antillas

Schistosoma mansoni control in Cul de Sac Valley, Saint Lucia. I. A two-year focal surveillance-mollusciciding programme for the control of Biomphalaria glabrata.

An area-wide mollusciciding campaign in Cul de Sac valley, St. Lucia reduced incidence of Schistosoma mansoni from 22% to 4.3% between 1970 and 1975. Following this, a two-year focal surveillance-mollusciciding programme was introduced. Sites of potential transmission of S. mansoni were identified and routinely searched for Biomphalaria glabrata. If found, the site was treated with clonitralide 25% emulsifiable concentrate. Two chemotherapy campaigns supplemented the snail control programme. As a result of the combined measures, incidence of the infection dropped from 4.3% to 1.0% and from 2.2% to 0.6% in areas originally of high and low transmission respectively. The cost of protecting the 7,000 population was US $20,362: of these costs, labour absorbed 68%, transport 24%, equipment 4% and molluscicide 4%. The cost per person per year protected was US $1.45 which compares favourably with the $3.24 of the previous scheme. Although effective and relatively cheap, this programme was still dependent on a high standard of supervision for maximum benefit.

Laboratory and field trials of a slow-release copper molluscicide in St. Lucia.

Tests of a slow-release molluscicide containing 50% copper sulfate were under-taken in laboratory and field situations in St. Lucia. In laboratory trials, a granule form of the molluscicide produced 100% mortality of Biomphalaria glabrata down to 4 mg/liter active ingredient (a.i), while the pellet form produced 100% mortality down to 8 mg/liter a.i. In field trials, a dose of 100 mg/liter a.i. in granule form caused mortality of B. glabrata in banana drains but had no effect on B. glabrata populations in a marsh habitat. In both habitats, the dose of 100 mg/liter produced mortality of other molluscan fauna which caused changes in the molluscan diversity indices. This failure in field trials may have been due to dilution of copper levels caused by flooding and also by uptake of copper by mud and algae.

La esquistosomiasis y sus huéspedes intermediarios en las Pequeñas Antillas / Schistosomiasis and its intermediate hosts in the Lesser Antillean Islands

La esquistosomiasis representa una amenaza importante para la salud en la región del Caribe. Este artículo analiza la situación en relación con esta enfermedad y diversos factores que contribuyen a su transmisión en las Pequeñas Antillas (AU)