Phylogeographical Studies of Ascaris spp. Based on Ribosomal and Mitochondrial DNA Sequences |
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Authors: | Serena Cavallero Viliam Snabel Francesca Pacella Vitantonio Perrone Stefano D'Amelio |
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Affiliation: | 1. Department of Public Health and Infectious Diseases, Section of Parasitology, Sapienza University of Rome, Rome, Italy.; 2. Institute of Parasitology, Slovak Academy of Sciences, Kosice, Slovakia.; 3. Az. USL Roma B, Servizio Veterinario, Dip. di Prevenzione, Rome, Italy.; National Institute of Parasitic Diseases China CDC, China, |
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Abstract: | BackgroundThe taxonomic distinctiveness of Ascaris lumbricoides and A. suum, two of the world''s most significant nematodes, still represents a much-debated scientific issue. Previous studies have described two different scenarios in transmission patterns, explained by two hypotheses: (1) separated host-specific transmission cycles in highly endemic regions, (2) a single pool of infection shared by humans and pigs in non-endemic regions. Recently, A. suum has been suggested as an important cause of human ascariasis in endemic areas such as China, where cross-infections and hybridization have also been reported. The main aims of the present study were to investigate the molecular epidemiology of human and pig Ascaris from non-endemic regions and, with reference to existing data, to infer the phylogenetic and phylogeographic relationships among the samples.Methodology151 Ascaris worms from pigs and humans were characterized using PCR-RFLP on nuclear ITS rDNA. Representative geographical sub-samples were also analysed by sequencing a portion of the mitochondrial cox1 gene, to infer the extent of variability at population level. Sequence data were compared to GenBank sequences from endemic and non-endemic regions.Principal FindingsNo fixed differences between human and pig Ascaris were evident, with the exception of the Slovak population, which displays significant genetic differentiation. The RFLP analysis confirmed pig as a source of human infection in non-endemic regions and as a corridor for the promulgation of hybrid genotypes. Epidemiology and host-affiliation seem not to be relevant in shaping molecular variance. Phylogenetic and phylogeographical analyses described a complex scenario, involving multiple hosts, sporadic contact between forms and an ancestral taxon referable to A. suum.Conclusions/SignificanceThese results suggest the existence of homogenizing gene flow between the two taxa, which appear to be variants of a single polytypic species. This conclusion has implications on the systematics, transmission and control programs relating to ascariasis. |
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