A Comparative Study of Physical and Chemical Control of the Intermediate Host of Schistosoma mansoni

Abstract

Schistosomiasis is a harmful disease often caused by the parasite, Schistosoma mansoni that infects more than 200 million people worldwide (Steinauer 2008). S. mansoni undergoes a complex life cycle in which it infects an intermediate host, Biomphalaria glabrata, a species of snail, before infecting humans as its definitive host (Roberts 2009). The disease of schistosomiasis becomes chronic upon multiple, repeated infections of the parasite (Roberts 2009). Therefore, diminishing the amount of hosts that could produce a large percentage of the infective stage of the parasite would be greatly beneficial to highly infected areas, to lessen the chances of obtaining chronic cases of the disease. The contamination of water sources with human waste is the most important epidemiological factor in schistosomiasis, and can be understood as the root of the problem regarding efforts of control (Roberts 2009). The availability of the suitable snail intermediate host will determine the endemicity of the S. mansoni species (Roberts 2009). For, without the presence of the necessary intermediate host, the parasite could not complete its life cycle and further spread the disease. This study aims to find a sustainable and effective control method to implement in western Kenya where the number of schistosomiasis cases is high (Hotez 2008). By testing both physical and chemical control methods on the B. glabrata population, the resulting effect on the snail population and the prevalence of the disease in the surrounding community will be assessed. The Nairobi province of western Kenya, contains a river system consisting of three parallel rivers equal distances apart. The northernmost, Mathare River will be used as a control where snail populations and relative schistosomiasis infections will be monitored during the course of the study. The Nairobi River will serve as a site for physical removal of snails using scoop and netting systems. The Motione-Ngong River will be implemented with a niclosamide molluscicide treatment, and relative effects on the species of snail will be recorded. It is the hope of the proposal that after the length of the study at least one of the implemented methods will demonstrate success in controlling intermediate host populations and could be manipulated to be sustainable within the impoverished communities to continue control of transmission of this prevalent disease.