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Wolfson Research Institute for Health and Wellbeing

Wolfson Fellow

Publication details for Dr Mark Booth

Kariuki, H.C., Madsen, H., Ouma, J.H., Butterworth, A.E., Dunne, D.W., Booth, M., Kimani, G., Mwatha, J.K., Muchiri, E. & Vennervald, B.J. (2013). 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. Parasites & Vectors 6(1): 107.

Author(s) from Durham

Abstract

Background: Schistosoma 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.
Methods: In 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.
Results: After 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.
Conclusion: The 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.