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.