Molecular genetic characterization of the cervid strain ('northern form') of Echinococcus granulosus.

We have used a number of molecular genetic approaches to characterize the cervid strain ('northern form') of Echinococcus granulosus. PCR-RFLP analysis of the nuclear ITS1 region of the rDNA repeat can readily distinguish the cervid form from other strains of E. granulosus. The complexity of the RFLP patterns obtained suggests that a number of distinct ITS1 types are present in this strain which may represent an inter-strain E. granulosus hybrid. Mitochondrial CO1 sequence of the cervid genotype was ambiguous at 18 positions and closely resembles a cluster of previously characterized E. granulosus genotypes, G1 (common, domestic sheep)/G2 (Tasmanian sheep)/G3 (buffalo). In contrast, mitochondrial ND1 sequence, although unique, suggests that the cervid form is most similar to strains represented by the G6 (camel)/G7 (pig) genotypes. We assume that the CO1 and ND1 sequences obtained for the cervid genotype are linked in a single mitochondrial genome although this is difficult to explain if conventional molecular genetics of mitochondrial DNA are assumed. Based on its unique ND1 sequence and ITS1 PCR-RFLP pattern, the cervid strain appears to represent a distinct genotype (designated G8) of E. granulosus.