Electrophoretic analysis of genetic variation in Echinococcus granulosus from domestic hosts in Australia

Abstract

Allozyme variation was examined in 26 isolates of the Australian mainland sheep strain and 13 isolates of the Tasmanian sheep strain of Echinococcus granulosus. One isolate of the British horse strain was examined for comparative purposes. Fifteen enzymes, encoded by 20 presumptive loci, were analysed. Differences in expression of enzymes were found between adult worms, protoscoleces, and fluid and germinal layer from hydatid cysts. Major differences were found at nine enzyme loci between the isolate of the British horse strain and isolates of the Australian mainland and Tasmanian sheep strains. The Australian strains differed in allelic frequencies at two loci, but no diagnostic alleles were found. Allozyme variation was detected within both the Australian strains. The proportion of polymorphic loci (P) was estimated at 0.15 for both strains, while the total gene diversity ( H) was 0.02 for the mainland strain and 0.06 for the Tasmanian strain. The pattern of genetic variation over geographic areas and the absence of multi-locus associations suggested that cross-fertilization was occurring in both strains. However, deficiencies of heterozygotes at some loci provided evidence for self-fertilization. These data are discussed in relation to proposed models of strain variation in E. granulosus.