Fascioliasis is a disease caused by Fasciola hepatica worldwide transmitted by lymnaeid snails mainly of the Galba/Fossaria group and F. gigantica restricted to parts of Africa and Asia and transmitted by Radix lymnaeids. Concern has recently risen regarding the high pathogenicity and human infection capacity of F. gigantica. Abnormally big-sized fasciolids were found infecting sheep in Ecuador, the only South American country where F. gigantica has been reported. Their phenotypic comparison with F. hepatica infecting sheep from Peru, Bolivia and Spain, and F. gigantica from Egypt and Vietnam demonstrated the Ecuadorian fasciolids to have size-linked parameters of F. gigantica. Genotyping of these big-sized fasciolids by rDNA ITS-2 and ITS-1 and mtDNA cox1 and nad1 and their comparison with other countries proved the big-sized fasciolids to belong to F. hepatica. Neither heterozygotic ITS position differentiated the two species, and no introgressed fragments and heteroplasmic positions in mtDNA were found. The haplotype diversity indicates introductions mainly from other South American countries, Europe and North America. Big-sized fasciolids from Ecuador and USA are considered to be consequences of F.gigantica introductions by past livestock importations. The vector specificity filter due to Radix absence should act as driving force in the evolution in such lineages.

Contrary to the majority of other Trematoda, Schistosoma species are gonochoric. Consequently, in endemic areas where several schistosome species overlap and can co-infect the same definitive host, there may be frequent opportunities for interspecific pairing. Our experimental study provides novel insight on the pairing behavior between Schistosoma bovis and S. mansoni in mixed infections in mice. We used six mate choice experiments to assess mating interactions between the two schistosome species. We show that mating between the two Schistosoma species is not random and that S. mansoni exhibits greater mate recognition compared to S. bovis. We also performed reciprocal crosses (male S. mansoni × female S. bovis) and (female S. mansoni × male S. bovis) that produce active swimming miracidia. These miracidia were genotyped by ITS2 sequencing and proposed for mollusc infection. Molecular analyses show that all the miracidia are parthenogenetically produced (i.e., their harbor the mother ITS2 genotype) and as a consequence can only infect the mollusc of the maternal species. Offspring produced by male S. mansoni × female S. bovis pairing can only infect Bulinus truncatus whereas offspring produced by female S. mansoni × male S. bovis can only infect Biomphalaria glabrata snails. Evolutionary and epidemiological consequences are discussed.

Schistosomiasis is a Neglected Tropical Disease caused by trematode species of the genus Schistosoma. Both, autochthonous and imported cases of urogenital schistosomiasis have been described in Europe. The present study focuses on eggs, considered pure S. haematobium by genetic characterisation (intergenic ITS region of the rDNA and cox1 mtDNA). A phenotypic characterisation of S. haematobium eggs was made by morphometric comparison with experimental populations of S. bovis and S. mansoni, to help in the diagnosis of S. haematobium populations infecting sub-Saharan migrants in Spain. Analyses were made by Computer Image Analysis System (CIAS) applied on the basis of new standardised measurements and geometric morphometric tools. The principal component analysis (PCA), including seventeen non-redundant measurements, showed three phenotypic patterns in eggs of S. haematobium, S. bovis and S. mansoni. PCA showed that the S. bovis population presented a large egg size range with a pronouncedly larger maximum size. Similarly, S. bovis shows bigger spine values than S. haematobium. Mahalanobis distances between each pair of groups were calculated for each discriminant analysis performed. In general, S. mansoni and S. bovis present larger distances between them than with S. haematobium, i.e. they present the greatest differences. Regarding the spine, S. haematobium and S. mansoni are the most distant species. Results show the usefulness of this methodology for the phenotypic differentiation between eggs from these Schistosoma species, capable of discerning morphologically close eggs, as is the case of the haematobium group. Schistosoma egg phenotyping approaches may be applied to assess not only hybrid forms but also potential influences of a variety of other factors.

Mitochondrial cox 1 and nuclear ribosomal ITSs are commonly combined to distinguish Schistosoma species and identify hybrids in endemic countries but very rarely applied to patients diagnosed in Europe despite the increasing arrival of migrants in southwestern Europe. To assess whether those migrants are carriers of pure or hybrid schistosomes, a complete genetic characterization of Schistosoma entering Spain is performed. A total of 759 eggs (from urine + stools) from 58 patients from 8 African countries were individually processed to describe their mito‐nuclear signature by cox 1 rapid diagnostic multiplex one‐step polymerase chain reaction (RD‐PCR) and ITS‐2/18S sequencing and haplotype identification by means of the complete ITS1‐5.8S‐ITS2 rDNA and cox 1 sequencing. Combined nuclear and mitochondrial DNA markers in sub‐Saharan migrants residing in Spain are described for the first time. Twenty‐two (40.74%) patients were simultaneously carrying pure and hybrid eggs in their urine. S chistosoma haematobium × S. bovis (68.18%) and S. haematobium × S. curassoni (31.82%) hybrid combinations were the most frequent. Six (one pure and five hybrid) and two (pure) mito‐nuclear signatures, in urine and stools, respectively, and 12 nuclear and 61 mitochondrial imported haplotypes were found. This study highlights the genetic complexity of pure and hybrid schistosomes that enter Spain, and consequently Europe, and contributes to the following: correlate the geographical origin of patients with pure and/or hybrid genetic types; detect the presence of hybrids “at distance” (hybrids in migrants from Guinea‐Bissau and Mauritania are first time detected); correlate molecular haplotypes with pathologies, clinical pictures, and treatment responses; and, importantly, warn about possible sources of autochthonous transmission.

Schistosome eggs play a key role in schistosomiasis diagnosis and research. The aim of this work is to morphogenetically study the eggs of Schistosoma haematobium found in sub-Saharan migrants present in Spain, analyzing their morphometric variation in relation to the geographical origin of the parasite (Mali, Mauritania and Senegal). Only eggs considered “pure” S. haematobium by genetic characterization (rDNA ITS-2 and mtDNA cox1) have been used. A total of 162 eggs obtained from 20 migrants from Mali, Mauritania and Senegal were included in the study. Analyses were made by the Computer Image Analysis System (CIAS). Following a previously standardized methodology, seventeen measurements were carried out on each egg. The morphometric analysis of the three morphotypes detected (round, elongated and spindle) and the biometric variations in relation to the country of origin of the parasite on the egg phenotype were carried out by canonical variate analysis. Mahalanobis distances, when all egg measurements were analyzed, showed differences between: (i) Mali-Mauritania, Mali-Senegal and Mauritania-Senegal in the round morphotype; (ii) Mali-Mauritania and Mauritania-Senegal in the elongated morphotype; and (iii) Mauritania-Senegal in the spindle morphotype. Mahalanobis distances, when spine variables were analyzed, showed differences between Mali-Senegal in the round morphotype. In conclusion, this is the first phenotypic study performed on individually genotyped “pure” S. haematobium eggs, allowing the assessment of the intraspecific morphological variations associated with the geographical origin of the schistosome eggs.

In Europe, imported schistosomiasis affects a diverse range of patients, including migrants, travellers, visiting friends and relatives, and expatriates who have lived in endemic areas. The variety of regions linked to these patients’ origins or destinations increases the likelihood of infections from different Schistosoma species and hybrids. This work aims to address the multidisciplinary challenges posed by ‘pure’ and hybrid Schistosoma species in southwestern Europe. It explores (i) the role of molecular analysis in identifying species and hybrids, (ii) the importance of morphogenetic studies of Schistosoma eggs, (iii) the potential risk of hybrid Schistosoma infections emerging in Europe and (iv) the clinical management, diagnostis and treatment of schistosomiasis in non-endemic European countries. The study includes examples of ‘pure’ and hybrid species detected in a tropical medicine unit in Almería, Spain. In this context, the complexity of managing not only the clinical aspects, diagnosis and treatment of this disease, but also the need and readiness to quantify the risks and prevent future outbreaks of schistosomiasis in Europe are evident. Schistosoma hybrids potentially able to adapt to new European habitats are a challenge, which highlights the need for appropriate surveillance and preventive measures to avoid the introduction of schistosomiasis into Europe. This article is part of the Science+ meeting issue ‘Parasite evolution and impact in action: exploring the importance and control of hybrid schistosomes’.