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

The effect on transmission of Schistosoma mansoni of a focal snail control programme was investigatsd over four years amongst approximately 1250 people living in 5 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 8mg/litre clonitralide every four weeks. Only proven and potential transmission sites were treated (AU)

Biological control of snail intermediate hosts of schistosomiasis - abstract

Chemical control of the intermediate host snails of bilharzia is an accepted method of interrupting transmission. Recently, the wisdom of using non-specific molluscides on a large scale has been questioned and escalating chemical costs have given further stimulus to the search for alternative control methods. The various constraints (predation, competition for food, over-crowding, disease and adverse water conditions) which affect both snail and parasite populations are discussed with particular reference to those which might be exploited for control purposes. In general, those predators or competitors which have evolved together with a target species are unsuitable as control agents since they already co-exist. Thus most successful biological control has involved the introduction of exotic species. In the Caribbean three exotic snail species have recently been accidentally introduced and one of them, Thiara granifera, is spreading rapidly throughout the region. The history of its spread from the Far East to Florida, Puerto Rico and southwards to Grenada is discussed together with evidence that it can be a useful competitor for Biomphalaria glabrata, the intermediate host of bilharzia (AU)

Schistosomiasis and its intermediate hosts in the Lesser Antillean Islands of the Caribbean

This article reviews the history, present status, and potential for spread of intestinal schistosomiasis in the Lesser Antilles in the light of factors which contribute to its transmission.(AU)

Schistosoma mansoni control in Cul de Sac Valley, Saint Lucia. 1. 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 percent to 4.3 percent 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 clonitrralide 25 percent 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 percent to 1.0 percent and from 2.2 percent to 0.6 percent 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 percent, transport 24 percent, equipment 4 percent and molluscicide 4 percent. 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. (AU)

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

Tests of a slow-release molluscicide containing 50 percent copper sulfate were undertaken in laboratory and field situations in St. Lucia. In laboratory trials, a granule form of the molluscicide produced 100 percent mortality of Biomphalaria glabrata down to 4 mg.liter active ingredient (a.i), while the pellet form produced 100 percent 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 100mg/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 (AU)