Aspects of the speciation of Echinococcus granulosus in Australia

Lakshmi Malkanthi Kumaratilake

In order to determine whether intraspecific variants of E. granulosus occur in Australia, different populations of the parasite from domestic and wild animal hosts in geographically segregated areas of Australia were compared by applying several criteria simultaneously, in addition to conventional morphological studies. Both the metacestode and strobilar stages of E. granulosus from naturally infected animals were studied as well as adult worms of known age and origin from experimentally infected domestic dogs. The results of comparative morphological, epidemiological, developmental (in vivo and in vitro), host specificity and biochemical studies indicate that at least three different intraspecific variants, or strains, of E. granulosus exist in Australia. One domestic strain, primarily perpetuated in a typical sheep/dog cycle, is found throughout the mainland whereas another is restricted to domestic sheep in Tasmania. The third is a sylvatic strain perpetuated amongst macropod marsupials and dingoes on the mainland of Australia. This study was further extended by comparing various populations of Echinococcus from different countries in an attempt to determine the relationship of E. granulosus in Australia to the parasite in other countries. Results of these comparative studies indicated that E. granulosus of domestic animal origin on the mainland of Australia is the same strain as that found in sheep in New Zealand and the United Kingdom. These studies also provided evidence to substantiate the existence of several distinct intraspecific variants of E. granulosus in various parts of the world. The present investigation has demonstrated the importance of considering a variety of criteria in studies on the speciation of Echinococcus. An attempt was made to evaluate and define criteria which are of value in differentiating and characterising intraspecific variants of Echinococcus. In particular, a reproducible procedure for comparing the soluble proteins of different populations of Echinococcus has been established, and a detailed reappraisal undertaken of morphological characters useful in differentiating populations at both the specific and intraspecific levels.

Aspects of the speciation of Echinococcus granulosus in Australia

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