Discussion

Human schistosomiasis is a neglected tropical disease affecting millions of people predominantly in South America, Asia and Sub-Saharan Africa (SSA). Of the several species causing this debilitating disease, Schistosoma haematobium, the causative agent of urogenital schistosomiasis, has been somewhat overlooked in terms of research efforts, yet infects more people than all other schistosomes combined and displays unexplained genetic homogeneity throughout SSA. Eswatini (formerly Swaziland) is a schistosomiasis endemic country that has not been genetically characterised, and through observational research on egg morphology, exhibits high levels of inter-species hybridisation.

S. haematobium miracidia were collected in May 2019 from 19 infected children in five known transmission localities from all four administrative areas of Eswatini (Hhohho, Manzini, Shiselweni and Lubombo). A partial fragment of the mitochondrial cytochrome oxidase subunit I (cox1) and NADH-dehydrogenase subunit 5 (nad5) genes were amplified for each miracidia to confirm species identification and genetic diversity. Furthermore, the nuclear internal transcribed spacer 1 (ITS1) was sequenced to identify if inter-species hybridisation events had occurred. 

 From the 148 S. haematobium miracidia molecularly analysed, there was no evidence of species hybridisation in the schistosomes as is observed elsewhere in SSA. However, cox1 haplotype diversity in the Eswatini S. haematobium larvae was shown to exhibit 11 unique haplotypes in just a small subset of samples collected from the 19 infected individuals. This is in stark contrast to the one predominant cox1 haplotype seen throughout continental African strains. It was also observed that nad5 sequence data offered less genetic diversity than cox1 data, displaying six unique haplotypes. 

The high genetic diversity of S. haematobium in Eswatini is unlike the norm seen throughout mainland Africa that displays unusual uniformity. This suggests that schistosomes being transmitted in Eswatini have experienced a different evolutionary past to the rest of the continent. For example, not being subjected to the same selection pressures such as Mass Drug Administration (MDA) or not undergoing the same species mixing due to a restricted freedom of movement. In addition, nad5 was found to have lower genetic diversity and offered no further molecular information than cox1, and therefore is proposed here as being less useful for exploring the genetic diversity of schistosomes in molecular epidemiology studies.