Molecular epidemiology of cystic echinococcosis
Echinococcus granulosus exhibits substantial genetic diversity that has important implications for the design and development of vaccines, diagnostic reagents and drugs effective against this parasite. DNA approaches that have been used for accurate identification of these genetic variants are presented here as is a description of their application in molecular epidemiological surveys of cystic echinococcosis in different geographical settings and host assemblages. The recent publication of the complete sequences of the mitochondrial (mt) genomes of the horse and sheep strains of E. granulosus and of E. multilocularis, and the availability of mt DNA sequences for a number of other E. granulosus genotypes, has provided additional genetic information that can be used for more in depth strain characterization and taxonomic studies of these parasites. This very rich sequence information has provided a solid molecular basis, along with a range of different biological, epidemiological, biochemical and other molecular-genetic criteria, for revising the taxonomy of the genus Echinococcus. This has been a controversial issue for some time. Furthermore, the accumulating genetic data may allow insight to several other unresolved questions such as confirming the occurrence and precise nature of the E. granulosus G9 genotype and its reservoir in Poland, whether it is present elsewhere, why the camel strain (G6 genotype) appears to affect humans in certain geographical areas but not others, more precise delineation of the host and geographic ranges of the genotypes characterised to date, and whether additional genotypes of E. granulosus remain to be identified.
Key Words: Echinococcus; Echinococcus granulosus; Echinococcus multilocularis; echinococcosis; strain variation; genotype; horse-dog strain; sheep-dog strain; mitochondrial DNA; cox1 gene; nad1 gene; taxonomy.
c1 Molecular Parasitology Laboratory, Division of Infectious Disease and Immunology, The Queensland Institute of Medical Research, Post Office Royal Brisbane Hospital, Queensland 4029, Australia. Tel: +61-7-33620401. Fax: +61-7-33620104. E-mail: donM@qimr.edu.au