Extant interspecific hybridization among trematodes within theSchistosoma haematobiumspecies complex in Nigeria

Abstract

AbstractBackgroundNatural interspecific hybridization between the human parasite (Schistosoma haematobium[Sh]) and bovine parasites (S. bovis[Sb], S. curassoni[Sc]) is increasingly reported in Africa. We developed a multi-locus PCR DNA-Seq strategy that amplifies two unlinked nuclear (transITS,BF) and two linked organellar genome markers (CO1,NAD5) to genotypeS. haematobiumeggs collected from infected people in Ile Oluji/Oke Igbo, Ondo State (an agrarian community) and Kachi, Jigawa State (a pastoral community) in Southwestern and Northern Nigeria, respectively.Principal FindingsWe applied this methodology against 57 isolates collected from a total of 219 participants. All patients from Jigawa state were infected with just one of two haplotypes of anS. haematobium x S. bovishybrid based on sequences obtained atCO1,NAD5, transITSandBFmarkers. Whereas samples collected from Ondo state were varied. Mitonuclear discordance was observed in all 17 patients, worms possessed anSbmitochondrial genome but one of four different haplotypes at the nuclear markers, either admixed (heterozygous betweenSh x ScorSh x Sb) at both markers (n=10),ShatBFand admixed attransITS(Sh x Sc) (n=5), admixed (Sh x Sc) atBFand homozygousScattransITS(n=1) or homozygousShatBFand homozygousScattransITS(n=1).SignificancePrevious work suggested that zoonotic transmission ofS. bovisin pastoral communities, where humans and animals share a common water source, is a driving factor facilitating interspecific hybridization. However, our data showed that all isolates were hybrids, with greater diversity identified in Southwestern Nigeria, a non-pastoral site. Further, one patient possessed anS. bovismitochondrial genome but was homozygous forS. haematobiumatBFand homozygous forS. curassoniattransITSsupporting at least two separate backcrosses in its origin, suggesting that interspecific hybridization may be an ongoing process.Author SummaryInterspecific hybridization between trematode parasites poses serious health risks to humans. Many systems have shown possible hybridization between different schistosome species. As evidence of natural hybridization between humanS. haematobiumand animalS. bovisorS. curassonihas grown in recent years, epidemiological surveys across potential hybrid zones are required, particularly in endemic African regions. According to several reports, indiscriminate human-animal water contact is a major factor contributing to hybridization of human and animal schistosomes. We collected and genotyped 57 parasite isolates from pastoral and non-pastoral communities in Kachi, Jigawa state, and Ile Oluji/Oke Igbo, Ondo state, Nigeria to screen for hybrids. In both sites, we foundSchistosomahybrids with mitonuclear discordance and repeated backcrossing betweenS. haematobium,S. bovis, andS. curassoni. Contrary to previous reports,Schistosomahybrids appear to be widespread and not solely dependent on human-animal water interactions.