Abstract
Schistosomes cause schistosomiasis, the world’s second most important parasitic disease after malaria in terms of public health and social-economic impacts. A peculiar feature of these dioecious parasites is their ability to produce viable and fertile hybrid offspring. Originally only present in the tropics, schistosomiasis is now also endemic in southern Europe. Based on the analysis of two genetic markers the European schistosomes had previously been identified as hybrids between the livestock- and the human-infective species Schistosoma bovis and Schistosoma haematobium, respectively. Here, using PacBio long-read sequencing technology we performed genome assembly improvement and annotation of S. bovis, one of the parental species for which no satisfactory genome assembly was available. We then describe the whole genome introgression levels of the hybrid schistosomes, their morphometric parameters (eggs and adult worms) and their compatibility with two European snail strains used as vectors (Bulinus truncatus and Planorbarius metidjensis). Schistosome-snail compatibility is a key parameter for the parasites life cycle progression, and thus the capability of the parasite to establish in a given area. Our results show that this Schistosoma hybrid is strongly introgressed genetically, composed of 77% S. haematobium and 23% S. bovis origin. This genomic admixture suggests an ancient hybridization event and subsequent backcrosses with the human-specific species, S. haematobium, before its introduction in Corsica. We also show that egg morphology (commonly used as a species diagnostic) does not allow for accurate hybrid identification while genetic tests do.
Highlights
Schistosomes are dioecious parasitic flatworms, responsible for the major Neglected Tropical Disease (NTD) schistosomiasis
A total of 44 eggs collected from hamsters infected with the European S. haematobium-bovis hybrid were examined for morphological characterization
To date genomic evidence indicates that only a small proportion of S. bovis seems to have introgressed in the genomic background of S. haematobium (i.e. 3–8%), introgression from S. bovis is widespread across S. haematobium populations in endemic areas
Summary
Schistosomes are dioecious parasitic flatworms, responsible for the major Neglected Tropical Disease (NTD) schistosomiasis. The epidemiological statistics associated with this disease are sobering: 800 million people are at risk in 78 countries, mostly concentrated in sub-Saharan Africa; 230 million are infected and the disease causes more than 200,000 deaths each year as well as between 1.7 and 4.5 million Disability Adjusted Life Years (DALYs) [1]. The most exposed groups are children and young adults who have activities linked to contaminated freshwater environments. Schistosomiasis severely impacts livestock in Africa and Asia with over 165 million animals estimated to be infected [2]. The parasites have a complex life cycle that includes passage through specific freshwater snail intermediate hosts (hereafter termed vectors) in which the parasites undergo clonal multiplication, and a final vertebrate definitive host in which, adult worms sexually reproduce. The liberation of Schistosoma eggs into the host tissues is the principal cause of chronic and acute morbidity [3]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
