Genetic heterogeneity within Echinococcus granulosus: isolates from different hosts and geographical areas characterized with DNA probes.

A segment of the ribosomal RNA gene of Schistosoma mansoni and a DNA fragment specific to Echinococcus granulosus, cloned in plasmids, have been used as DNA probes to assess the extent of genetic variability within E. granulosus and some distinct strains have been identified. The DNA analysis, involving restriction endonuclease digestion and Southern blot hybridization with the probes, did not demonstrate any significant genetic variation within the U.K. horse/dog or sheep/dog strains but confirmed the distinctiveness of the two strains shown in previous studies. The sheep/dog strain was shown to be cosmopolitan in its distribution and fertile bovine material originating from the United Kingdom, Kenya, Spain and India conformed to this strain by DNA hybridization. In contrast, cattle isolates from Holland produced markedly different DNA hybridization banding profiles indicating that cattle can harbour more than one strain of E. granulosus. Similarly, it was shown that goats can harbour two different strains of E. granulosus, the sheep/dog strain and a form which infects camels. The strain of E. granulosus infecting equines in Spain and Ireland is genetically identical to that infecting horses in the United Kingdom. There is also a different strain infecting pigs in Poland and Yugoslavia. This pig/dog strain appears to be very similar genetically to the forms of E. granulosus which use camels and goats as intermediate hosts and is similar, though not identical, to the variant infecting Dutch cattle. It has been shown that E. granulosus material, fixed for a prolonged period in ethanol, or lyophilized, is amenable to DNA analysis and that it is possible to characterize the DNA of a single adult worm.