Genetic evidence for the role of non-human primates as reservoir hosts for human schistosomiasis

Background Schistosomiasis is a chronic parasitic disease, that affects over 207 million people and causes over 200,000 deaths annually, mainly in sub-Saharan Africa. Although many health measures have been carried out to limit parasite transmission, significant numbers of non-human primates such asChlorocebus aethiops(Ch.aethiops) (vervet) andPapio anubis(baboon) are infected withS.mansoni, notably in Ethiopia, where they are expected to have potentially significant implications for transmission and control efforts. Objective The objective of this study was to assess and compare the genetic diversity and population structure ofS.mansoniisolates from human and non-human primates free-ranging in close proximity to villages in selected endemic areas of Ethiopia. Methods A cross-sectional study was conducted in three transmission sites: Bochesa, Kime and Fincha. A total of 2,356S.mansonimiracidia were directly isolated from fecal specimens of 104 hosts (i.e. 60 human hosts and 44 non-human primates). We performed DNA extraction and PCR amplification using fourteen microsatellite loci. Results At population scale we showed strong genetic structure between the three sample sites. At the definitive host scale, we observed that host factors can shape the genetic composition of parasite infra-populations. First, in male patients, we observed a positive link between parasite genetic diversity and the age of the patients. Second, we observed a difference in genetic diversity which was high in human males, medium in human females and low in non-human primates (NHPs). Finally, whatever the transmission site no genetic structure was observed between human and non-human primates, however, there appears to be little barriers, if any, host specificity of theS.mansonipopulations with cross-host infections. Conclusion Occurrence of infection of a single host with multipleS.mansonistrains and inter- and intra-host genetic variations was observed. Substantial genetic diversity and gene flow across theS.mansonipopulation occurred at each site and non-human primates likely play a role in local transmission and maintenance of infection. Therefore, public health and wildlife professionals should work together to improve disease control and elimination strategies. Author summary Schistosomiasis is a chronic disease caused by flukes (trematodes). The definitive host spectrum of schistosomes, whether human, non-human primates (NHPs) or other mammals, is highly dependent on the schistosome species concerned. Genetic diversity and population structure studies ofS.mansonihave provided insights into the variation of natural populations. UnderstandingS.mansonigenetic diversity and population structure of isolates from human and non-human primate hosts living in close proximity showed the occurrence of infection of a single host with multipleS.mansonistrains and inter- and intra-host genetic variations. In this article, the researchers assert the fact that genetic approach reveals that parasites from the three different sites are independent. Thus, we could consider the three sites as geographical replicates showing the influence of NHPs in parasitic transmission in Ethiopia. This study provides insights into the epidemiology, genetic diversity and population structure ofS.mansoniin human and non-human primates in Ethiopia, all of which are crucial for the control of schistosomiasis.