Authors

Discussion

Hybridisation between species within the Schistosoma genus is an emerging public health problem. The hybridisation between Schistosoma bovis, a veterinary parasite, and S. haematobium, a human parasite is of great interest where it was responsible for the re-emergence of schistosomiasis in Southern Europe. The consequences of hybridisation and subsequent introgression can impact the host range, transmission, pathology and epidemiology of schistosomiasis. This study used available cox1 data to investigate the geographical and host structuring of S. bovis and S. haematobium-bovis hybrids across Africa. The cox1 dataset formed a complex and diverse haplotype network for S. bovis but, apart from two haplotypes, all (n=41) data from samples identified as S. haematobium-bovis hybrids formed two distinct genetic clusters. These clusters showed little diversity with the majority being identical mitotypes from different hosts and countries. Additionally, the clusters did not form part of the S. bovis network, which showed geographical structuring into West, Central and East African populations. The low genetic diversity observed within the S. haematobium-bovis hybrids suggests that selection or genetic bottlenecking may occur during hybridisation. There was also little apparent mixing between hybrid and S. bovis populations, suggesting that the hybrid genetic signatures seen in human hosts may be the result of past introgression. Findings in this study demonstrate the complexity and the subsequent challenges surrounding the origin, intermediate host range and host in which hybridisation occurs. Populations from different hosts are clearly mixing and there appears to be cross over between adjacent regions which is likely supported by livestock movement. The evolution of the Schistosoma genus and how they adapt to anthropogenic changes will aid in understanding the factors allowing the emergence and establishment of S. haematobium-bovis hybrids. Further studies are required to elucidate the risk factors associated with these hybrids populations, particularly the possibility of zoonotic transmission.