Current status of the genetics and molecular taxonomy ofEchinococcusspecies

Abstract

SUMMARYThe taxonomy ofEchinococcushas long been controversial. Based mainly on differences in morphology and host-parasite specificity characteristics, 16 species and 13 subspecies were originally described. Subsequently, most of these taxa were regarded as synonyms forEchinococcus granulosusand only 4 valid species were recognised:E. granulosus;E. multilocularis;E. oligarthrusandE. vogeli. But, over the past 50 years, laboratory and field observations have revealed considerable phenotypic variability between isolates ofEchinococcus, particularly those ofE. granulosus, which include differences in: morphology in both larval and adult stages, developmentin vitroandin vivo, host infectivity and specificity, chemical composition, metabolism, proteins and enzymes, pathogenicity and antigenicity. The application of molecular tools has revealed differences in nucleic acid sequences that reflect this phenotypic variation and the genetic and phenotypic characteristics complement the previous observations made by the descriptive parasitologists many years ago. The fact that some of these variants or strains are poorly or not infective to humans has resulted in a reappraisal of the public health significance ofEchinococcusin areas where such variants occur. A revised taxonomy for species in theEchinococcusgenus has been proposed that is generally accepted, and is based on the new molecular data and the biological and epidemiological characteristics of host-adapted species and strains.