Morphological and Genomic Characterisation of the Hybrid Schistosome Infecting Humans In Europe Reveals a Complex Admixture Between Schistosoma haematobium and Schistosoma bovis Parasites.

Schistosomes cause schistosomiasis, the worlds second most important parasitic disease after malaria. A peculiar feature of schistosomes is their ability to produce viable and fertile hybrids. Originally only present in the tropics, schistosomiasis is now also endemic in Europe. Based on two genetic markers the European species had been identified as a hybrid between the ruminant-infective Schistosoma bovis and the human-infective Schistosoma haematobium.\n\nHere we describe for the first time the genomic composition of the European schistosome hybrid (77% of S. haematobium and 23% of S. bovis origins), its morphometric parameters and its compatibility with the European vector snail and intermediate host Compatibility is a key parameter for the parasites life cycle progression. We also show that egg morphology (a classical diagnostic parameter) does not allow for differential diagnosis while genetic tests do so. Additionally, we performed genome assembly improvement and annotation of S. bovis, the parental species for which no satisfactory genome assembly was available.\n\nFor the first time since the discovery of hybrid schistosomes, these results reveal at the whole genomic level a complex admixture of parental genomes highlighting (i) the high permeability of schistosomes to other species alleles, and (ii) the importance of hybrid formation for pushing species boundaries not only conceptionally but also geographically.