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.