Long term study on the effect of mollusciciding with niclosamide in streamhabitats on the transmission of schistosomiasis mansoni after community-basedchemotherapy in Makueni District, Kenya

Abstract

Abstract Background Schistosoma mansoni infection is a persistent public health problemin many Kenyan communities. Although praziquantel is available, re-infectionafter chemotherapy treatment is inevitable, especially among children.Chemotherapy followed by intermittent mollusciciding of habitats ofBiomphalaria pfeifferi, the intermediate host snail, may havelonger term benefits, especially if timed to coincide with naturalfluctuations in snail populations. Methods In this cohort study, the Kambu River (Intervention area) was molluscicidedintermittently for 4 years, after mass chemotherapy with praziquantelin the adjacent community of Darajani in January 1997. The nearby ThangeRiver was selected as a control (Non-intervention area), and its adjacentcommunity of Ulilinzi was treated with praziquantel in December 1996. Snailnumbers were recorded monthly at 9–10 sites along each river, whilerainfall data were collected monthly, and annual parasitological surveyswere undertaken in each village. The mollusciciding protocol was adapted tolocal conditions, and simplified to improve prospects for widespreadapplication. Results After the initial reduction in prevalence attributable to chemotherapy, therewas a gradual increase in the prevalence and intensity of infection in thenon-intervention area, and significantly lower levels of re-infectionamongst inhabitants of the intervention area. Incidence ratio between areasadjusted for age and gender at the first follow-up survey, 5 weeksafter treatment in the non-intervention area and 4 months aftertreatment in the intervention area was not significant (few people turnedpositive), while during the following 4 annual surveys these ratios were0.58 (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 areaas a result of the mollusciciding. Following termination of themollusciciding at the end of 2000, snail populations and infections insnails increased again in the intervention area. Conclusion The results of this study demonstrate that in the Kenyan setting acombination of chemotherapy followed by intermittent mollusciciding can havelonger term benefits than chemotherapy alone.