Abstract
BackgroundSchistosoma mansoni infection is a persistent public health problem in many Kenyan communities. Although praziquantel is available, re-infection after chemotherapy treatment is inevitable, especially among children. Chemotherapy followed by intermittent mollusciciding of habitats of Biomphalaria pfeifferi, the intermediate host snail, may have longer term benefits, especially if timed to coincide with natural fluctuations in snail populations.MethodsIn this cohort study, the Kambu River (Intervention area) was molluscicided intermittently for 4 years, after mass chemotherapy with praziquantel in the adjacent community of Darajani in January 1997. The nearby Thange River was selected as a control (Non-intervention area), and its adjacent community of Ulilinzi was treated with praziquantel in December 1996. Snail numbers were recorded monthly at 9–10 sites along each river, while rainfall data were collected monthly, and annual parasitological surveys were undertaken in each village. The mollusciciding protocol was adapted to local conditions, and simplified to improve prospects for widespread application.ResultsAfter the initial reduction in prevalence attributable to chemotherapy, there was a gradual increase in the prevalence and intensity of infection in the non-intervention area, and significantly lower levels of re-infection amongst inhabitants of the intervention area. Incidence ratio between areas adjusted for age and gender at the first follow-up survey, 5 weeks after treatment in the non-intervention area and 4 months after treatment in the intervention area was not significant (few people turned positive), while during the following 4 annual surveys these ratios were 0.58 (0.39-0.85), 0.33 (0.18-0.60), 0.14 (0.09-0.21) and 0.45 (0.26-0.75), respectively. Snail numbers were consistently low in the intervention area as a result of the mollusciciding. Following termination of the mollusciciding at the end of 2000, snail populations and infections in snails increased again in the intervention area.ConclusionThe results of this study demonstrate that in the Kenyan setting a combination of chemotherapy followed by intermittent mollusciciding can have longer term benefits than chemotherapy alone.
Highlights
Schistosoma mansoni infection is a persistent public health problem in many Kenyan communities
A combination of chemotherapy and focal mollusciciding in Brazil reduced the prevalence of S. mansoni infection from between 12.5-40% to below 9% [9], while in the late 1950’s a combination of chemotherapy and mollusciciding helped to achieve the control of S. mansoni on Vieques Island in Puerto Rico [10]
There was less variation among sites; lowest counts were found in sites 2 and 11 and highest counts in sites 4, 6 and 7
Summary
Schistosoma mansoni infection is a persistent public health problem in many Kenyan communities. Chemotherapy with praziquantel, directed at Schistosoma mansoni infected primary school children, is an effective way of causing a rapid reduction in morbidity and in prevalence and intensity of infection. It has relatively little effect on transmission and regular re-treatment at intervals of one to three years is usually necessary [1,2,3,4]. In St. Lucia in the West Indies, a community based chemotherapy programme resulted in a rapid reduction in prevalence and intensity of infection, and focal snail control delayed or prevented the expected resurgence of transmission [8]. This approach has not been attempted in Kenya, and has not been undertaken anywhere in comparison with chemotherapy alone at the same time and under similar environmental conditions
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