Phylogeography of Schistosoma bovis, S. curassoni and associated S. haematobium group hybrids across sub-Saharan Africa; revealed by mitochondrial cox1 analyses)
Schistosomiasis is a chronic disease of both medical and veterinary importance. It is caused by diecious blood flukes belonging to the Schistosoma genus. Although species that infect humans have received much attention, there are also species that infect non-human hosts, with livestock (cows, sheep and goats) observed to have high burdens of disease. In Africa, there are five Schistosoma species infecting livestock of which S. bovis is the most widespread across sub-Saharan Africa. Recently, S. bovis has become a research focus mainly due to its ability to hybridize with the human infecting parasite, S. haematobium, with hybrids commonly be associated with human hosts.   In this study we analysed the mitochondrial cytochrome c oxidase subunit 1 (cox1) data to explore the geographical and host structuring of S. bovis, S. curassoni together with their S. haematobium group hybrids. The analysed data consisted of both published (n=258) and new (n=169) (generated as part of this study) cox1 sequences data from adult Schistosoma worms, miracidia and cercariae. The majority of the dataset consisted of S. bovis cox1 from S. bovis and S. haematobium-bovis hybrids sampled from across sun-Saharan Africa. All data were aligned, trimmed for uniformity and subjected to both phylogenetic and haplotype analyses.  The analyses revealed a complex population structure of S. bovis populations with a notable divide between East and West African S. bovis populations. No population structure was observed by mammalian host (rodents and livestock). S. curassoni also showed high levels of genetic diversity compared to S. haematobium and the hybrid populations. Considerable reduced genetic diversity was found in the S. haematobium-bovis hybrid populations compared to S. bovis populations with two distinct hybrid clusters observed. This clustering affect is indicative of ancient mt introgression events with limited mixing between the general S. bovis populations found in animals and the S. haematobium-bovis hybrids primarily found in humans.  Findings in this study demonstrate the complexity of the genetic diversity of different Schistosoma species whilst highlighting the need to analyse samples from both humans and animals to identify population structuring by geography and host. Further analyses of such samples at the genome wide level is certainly warranted to shed light on inter species hybridisation and the level of mixing between human and animal Schistosoma species.