Schistosomiasis--research to control.

Abstract

Abstract In three isolated valleys on the West Indian island of St. Lucia a comparative evaluation was made of snail control, chemotherapy, and provision of water supplies in the control of Schistosoma mansoni transmission. In Cul-de-Sac Valley, 4 years of area control of Biomphalaria glabrata by using 25% emulsifiable concentrate reduced the incidence of new S. mansoni infection in children up to 10 years old from 22% (1970–71) to 4% (1974–75). Prevalence among a cohort of >1- to 14-year-olds was reduced from 45% to 34%, intensity of infection fell, and the infection rate in sentinel snails decreased from 3.9% to 1.1%. In five villages on the south side of Riche Fond Valley water was provided to individual households and three simple swimming pools and five laundry units were built. With education, there was a 90% reduction in observed contact of the community with rivers and streams. All parameters of S. mansoni infection fell—incidence from 31% to 12%, prevalence among a >1- to 14-year-old cohort from 47% to 42%, and the sentinel snail infection rate from 0.5% to 0.2%. In a nearby comparison area with a communal water supply S. mansoni prevalence increased. In Marquis Valley hycanthone at a dose of 2.5 mg/kg body weight was offered to all found infected with S. mansoni at annual surveys in 1973 and 1974; those found infected in 1975 were given oxamniquine. After two chemotherapy campaigns incidence fell from 18.8% to 4.1%; no infections were found in sentinel or wild snails after the first treatment campaign. After 2 years of control, chemotherapy reduced incidence from 18.8% to 4%; snail control, from 22% of 9.8%; and water supplies, from 22.7% to 11.3%. Annual costs per capita in the first 2 years were $1.10 (chemotherapy), $3.70 (snail control), and $4.00 (water supplies). Chemotherapy was the cheapest and most rapidly effective method of achieving transmission control, and additionally provided disease control. A disadvantage, not shared by snail control, is that it requires population cooperation and a stable community. Cooperation, but not necessarily a stable community, is required for water supplies (which provide other social and medical benefits) to be effective.