Current concepts of snail control

Abstract

Schistosomiasis control was impossible without effective tools. Synthetic molluscicides developed in the 1950s spearheaded community level control. Snail eradication proved impossible but repeated mollusciciding to manage natural snail populations could eliminate transmission. Escalating costs, logistical complexity, its labour-intensive nature and possible environmental effects caused some concern. The arrival of safe, effective, single-dose drugs in the 1970s offered an apparently better alternative but experience revealed the need for repeated treatments to minimise reinfection in programmes relying on drugs alone. Combining treatment with mollusciciding was more successful, but broke down if mollusciciding was withdrawn to save money. The provision of sanitation and safe water to prevent transmission is too expensive in poor rural areas where schistosomiasis is endemic; rendering ineffective public health education linked to primary health care. In the tropics, moreover, children (the key group in maintaining transmission) will always play in water. Large scale destruction of natural snail habitats remains impossibly expensive (although proper design could render many new man-made habitats unsuitable for snails). Neither biological control agents nor plant molluscicides have proved satisfactory alternatives to synthetic molluscicides. Biologists can develop effective strategies for using synthetic molluscicides in different epidemiological situations if only, like drugs, their price can be reduced.

Longitudinal Study on the Natural Infection of Biomphalaria straminea and B. glabrata by Schistosoma mansoni in an Endemic Area of Schistosomiasis in Pernambuco, Brazil

“…However, the relatively high rates of natural infection obtained for B. straminea in the present study should discourage the introduction of a resistant strain of this species in this area. As pointed out by Sturrock (1995) there is a risk that the initially resistant strain could become more susceptible through hybridization with the local strain.…”

Effects of Bayluscide WP 70® on the Survival and Water-leaving Behaviour of Biomphalaria straminea, Snail Host of Schistosomiasis in Northeast Brazil

“…Although some resistance to niclosamide can be induced under extreme conditions of genetic selection (Sullivan et al 1984), there is no evidence of that occurring after years of continuous use in the field (Sturrock 1995). As low susceptibility to molluscicide may require higher doses of the product, it is advisable that snail populations be assayed, and lethal doses determined, before being subjected to control campaigns.…”

Hydrology and density feedbacks control the ecology of intermediate hosts of schistosomiasis across habitats in seasonal climates

“…Intervention effectiveness depends on ecological context and control methods (e.g., frequency and duration of molluscicide application), especially in seasonal climates (3). Insight into the population dynamics of the snails acting as intermediate hosts is therefore necessary to acquire an understanding of the ecology of the disease (8) and to minimize transmission through action aimed at snail population control (9).…”