Pollution-induced immunomodulation in biomphalaria glabrata; implications for its relationship with obligate parasite schistosoma mansoni

Abstract

Aquatic pollution from urban and industrial effluents represents a growing area of concern. The number and volume of xenobiotic chemicals in aquatic ecosystems is alarmingly high, due in part to increasing globalization and the associated demands. Invertebrates, in particular molluscs, represent species of great commercial importance and can therefore fail to be considered in terms of their significance in the transmission of human disease. Schistosoma mansoni is a trematode parasite transmitted to humans by aquatic snails of the genus Biomphalaria. S.mansoni infects up to 200 million people globally and transmission primarily occurs in developing countries with poor infrastructure, factors which also happen to be associated with high levels of aquatic pollution. Despite the medical importance of S.mansoni and its occurrence in potentially polluted environments, very few attempts have been made to study this parasite-host relationship in the context of ecotoxicology. In this thesis I have applied both adapted and novel approaches in order to combine the fields of parasitology and ecotoxicology toward a better understanding of the effects of globally-prevalent xenobiotic chemicals on the S.mansoni-B.glabrata relationship. In vitro assays, with various end-points, were performed based on exposure of hemocytes, the primary immune effector cells of molluscs, while whole snails were developmentally exposed to an effluent extract and subsequently infected as part of an in vivo study. Taken together, my results suggest that the immunocompetance of B.glabrata hemocytes is broadly reduced in the presence of DDE, BPA, E2 and an effluent extract; chemicals that occur at high levels in transmission countries. Reduction in the key hemocyte functions of motility, phagocytosis and encapsulation, caused by exposure to these chemicals, appears to be exacerbated by subsequent S.mansoni infection which results in an opportunity for increased parasite shedding. My hope is that this broad work will serve as a reference and facilitate more focused studies, particularly of a molecular and epidemiological nature, into what is an understudied and potentially very important topic with the potential for human health implications.