Intestinal and urinary schistosomiasis dynamics in sub-Saharan Africa

Abstract

Schistosomiasis is a chronic infection by a digean trematode of the genus Schistosoma. More than 207 million people are infected with this parasite, of which 120 million are symptomatic. There are two main species infecting humans in sub-Saharan Africa: Schistosoma haematobium and S. mansoni, both occur in areas with similar socio-economic and environmental conditions and often have matching distribution patterns. The principle aims of the research presented in this thesis were to further our understanding of schistosome population genetics, associated human host morbidity and chemotherapeutic treatment of schistosomes in relation to mixed species infections. Structured sampling of parasites and/or host traits from school-aged children at baseline and post Mass Drug Administration (MDA) in Niger and Kenya were performed. The results presented provided evidence for S. haematobium - S. mansoni interactions and their impact on the human host and on the parasite population. In Kenya coinfections had lower S. haematobium related morbidity relative to single S. haematobium infections pre and post MDA. Additionally parasite infra-populations from coinfected children had higher genetic diversity levels compared to single infected children in mixed infection foci. In Niger, an impact of MDA on the population genetics of S. mansoni was detected in one mixed infection village, characterised as a noticeable bottleneck effect, but not in the other. There was no apparent impact of MDA on the population genetics of S. haematobium. Conversely, in Kenya, a significant impact of MDA on both species was detected, with a bottleneck effect occurring on the S. haematobium population and conversely, an increase in genetic diversity in the S. mansoni population. The results of this thesis are discussed in terms of their implications on schistosome epidemiology and evolution, and in relation to the control of schistosomiasis in sub-Saharan Africa.