Abstract
Schistosomiasis remains a public health concern across sub-Saharan Africa; current control programmes rely on accurate mapping and high mass drug administration (MDA) coverage to attempt disease elimination. Inter-species hybridisation can occur between certain species, changing epidemiological dynamics within endemic regions, which has the potential to confound control interventions. The impact of hybridisation on disease dynamics is well illustrated in areas of Cameroon where urogenital schistosomiasis, primarily due to Schistosoma haematobium and hybrid infections, now predominate over intestinal schistosomiasis caused by Schistosoma guineensis. Genetic markers have shown the ability to identify hybrids, however the underlying genomic architecture of divergence and introgression between these species has yet to be established. In this study, restriction site associated DNA sequencing (RADseq) was used on archived adult worms initially identified as; Schistosoma bovis (n = 4), S. haematobium (n = 9), S. guineensis (n = 3) and S. guineensis x S. haematobium hybrids (n = 4) from Mali, Senegal, Niger, São Tomé and Cameroon. Genome-wide evidence supports the existence of S. guineensis and S. haematobium hybrid populations across Cameroon. The hybridisation of S. guineensis x S. haematobium has not been demonstrated on the island of São Tomé, where all samples showed no introgression with S. haematobium. Additionally, all S. haematobium isolates from Nigeria, Mali and Cameroon indicated signatures of genomic introgression from S. bovis. Adaptive loci across the S. haematobium group showed that voltage-gated calcium ion channels (Cav) could play a key role in the ability to increase the survivability of species, particularly in host systems. Where admixture has occurred between S. guineensis and S. haematobium, the excess introgressive influx of tegumental (outer helminth body) and antigenic genes from S. haematobium has increased the adaptive response in hybrids, leading to increased hybrid population fitness and viability.
Highlights
Urogenital schistosomiasis is a waterborne parasitic disease transmitted through certain species of freshwater snail inhabiting water bodies throughout much of sub-Saharan Africa [1]
The highest degree of genetic distinctiveness was exhibited by the S. bovis (QS. bovis = 100%) and S. guineensis isolates (QS. guineensis = 0.997% and QS. haematobium = 0.003%)
The S. haematobium isolates displayed a consistent degree of introgression of S. bovis (QS. haematobium = 0.983% and QS. bovis = 0.017%)
Summary
Urogenital schistosomiasis is a waterborne parasitic disease transmitted through certain species of freshwater snail inhabiting water bodies throughout much of sub-Saharan Africa [1]. The S. haematobium species group comprises eight other sister species including; S. intercalatum and S. guineensis causing human intestinal schistosomiasis, and S. bovis, S. mattheei, S. margrebowei, S. leiperi, S. curassoni and S. kisumuensis infecting various wildlife, ruminants and livestock. Efficacy of praziquantel on hybrid and mixed infections within humans remains strong [13,14], hybridisation events would directly impact current monitoring, evaluation and mapping of the disease within endemic areas [15,16,17]. Laboratory experiments have demonstrated that F1 and F2 hybrids between S. guineensis and S. haematobium exhibited a greater ability to infect snail intermediate hosts along with increased growth rate, reproductive potential and longevity [13,14,15]. The increased infection potential of hybrids across multiple species of freshwater snail host will increase hybrid populations ability to establish diseases within environments, increasing infection range [18,19]
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