Eco-toxicological investigations of freshwater pollution on the distribution and vector competence of Schistosoma host snails in freshwater streams in western Kenya.
Schistosomiasis, an acute and chronic parasitic disease caused by trematode worms of the genus Schistosoma, is a neglected tropical disease (NTD), affecting the poorest of the poor with infections particularly abundant among people living in rural or deprived urban or peri-urban settings. The WHO NTD roadmap set a goal of global elimination of schistosomiasis as a ‘public health problem’ by 2025. However, preventive chemotherapy through delivery of praziquantel by mass drug administration to those shown to be, or presumed to be, at-risk of infection and disease is currently the only intervention. To target such intervention at the right populations there is need to better map out disease risk. Transmission occurs when people suffering from schistosomiasis contaminate freshwater sources with their excreta containing parasite eggs which hatch in water. People become infected when larval forms of the parasite are released by freshwater snails that present the intermediate hosts. Despite the significant role of snails in disease transmission malacological studies are rare. In this project, we hypothesize that pesticide pollution may favour the development and spread of host snails through the depletion of antagonistic macroinvertebrate species, affect the development of the trematodes in their intermediate hosts, and may reduce predators of the free-swimming trematode life stages. This is a 3 year project, which started operating in March 2017. During the first phase of the project, changes in the abundance of host snails and composition of the macroinvertebrate community will be measured in relation to environmental variables. To date, we have mapped the study area, selected 50 diverse field sampling sites and implemented comprehensive sampling and habitat characterisations to identify risk factors associated with the distribution of host snails and trematodes. Furthermore, water and sediment sampling has been completed and further chemical analyses to associate abundance of snails with potential pollutants in the environment in ongoing. A clear understanding of the snails’ ecology is required to predict its distribution, vectorial capacity and consequently map disease risk.
Dr U Fillinger - PI.
Collaboration: Helmholtz Centre for Environmental Research, Germany (Co-PI: Matthias Liess). 2017-2020.