A molecular phylogeny of the genus Echinococcus

Abstract

Three nucleotide data sets, two mitochondrial (COI and ND1) and one nuclear (ribosomal ITS1), have been investigated in order to resolve relationships among species and strains of the genus Echinococcus. The data have some unusual properties in that mitochondrial heteroplasmy was detected in one strain of E. granulosus, and more than one class of ITS1 sequence variant can occur in a single isolate. The data failed to support the hypothesis that E. granulosus, as it is currently viewed, is a single valid species. Rather, the strains of E. granulosus seem to comprise at least three evolutionarily diverse groups, the sheep strain group, bovine strain group and horse strain group. Molecular distances between them are comparable to, or greater than, molecular evolutionary distances observed between recognized species. The affinities of the cervid strain of E. granulosus are unclear because of ambiguous data, but this strain does not appear to be ancestral to others. E. multilocularis may not be distinct from E. granulosus. However, the remaining two species. E. vogeli and E. oligarthrus appear distinct and rather distant from the first two. Based on the results presented here, taxonomic revision of the genus is clearly warranted.

Molecular epidemiology of cystic echinococcosis

“…Careful phylogenetic analysis of the mitochondrial sequence data, in combination with additional nuclear sequence data (Bowles et al 1995), formally demonstrated the evolutionary distinctiveness of the sheep and horse strains of E. granulosus. Confirmation of species identity was obtained after analysis of the complete mitochondrial genomes that were recently obtained for both strains and another taeniid cestode, Taenia crassiceps .…”

“…By contrast, there appears to be very limited genetic variation within E. multilocularis (McManus & Bryant, 1995 ;Haag et al 1997 ;Rinder et al 1997 ;Kedra et al 2000 a), and there are no available data to indicate that either E. vogeli or E. oligarthrus is variable. The term strain is used to describe variants that differ from other groups of the same species in gene frequencies or DNA sequences, and in one or more characters of actual or potential significance to the epidemiology and control of echinococcosis (Thompson & Lymbery, 1988 ;Bowles, Blair & McManus, 1995).…”

Species identification of human echinococcosis using histopathology and genotyping in northwestern China

“…Substantial genetic diversity of E. granulosus has led to the description of 10 genotypes (G1-10) (Bowles et al, 1992(Bowles et al, , 1995Bowles and McManus, 1993;Lavikainen et al, 2003;Nakao et al, 2007;Scott et al, 1997), and the G1 genotype has been proved to be cosmopolitan in its distribution and the major cause of human infection (McManus, 2002;Thompson and McManus, 2001). In China, previous genotypic analysis indicated the pathogenicity of the G6 genotype (dog/camel) in humans in Xinjiang autonomous region (Bart et al, 2006).…”

Phylogenetic Pattern, Evolutionary Processes and Species Delimitation in the Genus Echinococcus

“…By the mid-1990's it was suggested from phylogenetic analyses of both morphological (Lymbery, 1992) and mtDNA sequence data (Bowles et al, 1995;Lymbery, 1995) that E. granulosus was a paraphyletic group, with some strains being more closely related to E. multilocularis than to other strains within the complex. Initial taxonomic revisions split E. granulosus (sensu lato) into three species; E. equinus for G4, E. ortleppi for G5 and E. granulosus sensu stricto for G1, G2 and G3 Thompson and McManus, 2002).…”