DNA Multi-Marker Genotyping and CIAS Morphometric Phenotyping of Fasciola gigantica-Sized Flukes from Ecuador, with an Analysis of the Radix Absence in the New World and the Evolutionary Lymnaeid Snail Vector Filter

Resumen

Fascioliasis is a disease caused by <i>Fasciola hepatica</i> worldwide transmitted by lymnaeid snails mainly of the <i>Galba</i>/<i>Fossaria</i> group and <i>F. gigantica</i> restricted to parts of Africa and Asia and transmitted by <i>Radix</i> lymnaeids. Concern has recently risen regarding the high pathogenicity and human infection capacity of <i>F. gigantica</i>. Abnormally big-sized fasciolids were found infecting sheep in Ecuador, the only South American country where <i>F. gigantica</i> has been reported. Their phenotypic comparison with <i>F. hepatica</i> infecting sheep from Peru, Bolivia and Spain, and <i>F. gigantica</i> from Egypt and Vietnam demonstrated the Ecuadorian fasciolids to have size-linked parameters of <i>F. gigantica</i>. Genotyping of these big-sized fasciolids by rDNA ITS-2 and ITS-1 and mtDNA <i>cox</i>1 and <i>nad</i>1 and their comparison with other countries proved the big-sized fasciolids to belong to <i>F. hepatica</i>. 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 <i>F.</i><i>gigantica</i> introductions by past livestock importations. The vector specificity filter due to <i>Radix</i> absence should act as driving force in the evolution in such lineages.