Isolation and molecular characterization of a variant of Chinese gC-genotype II pseudorabies virus from a hunting dog infected by biting a wild boar in Japan and its pathogenicity in a mouse model.

We isolated a variant of Chinese pseudorabies virus from a hunting dog with symptoms similar to Aujeszky's disease and designated the isolate MY-1 strain. The dog developed symptoms 6 days after hunting and biting a wild boar and died the day after onset. The Bam HI restriction profile of MY-1 DNA was different from those of the Japanese reference strain Yamagata-S81 and two vaccine strains, Bartha and Begonia, and resembled Bam HI-RFLP (restriction fragment length polymorphism) type IV. Complete nucleotide sequences were determined, and phylogenetic analyses revealed that MY-1 belonged to the same cluster of old Chinese strains and variant strains isolated recently in China, but most of the open reading frames of MY-1 were located on a different branch from those of these Chinese strains. Based on a gC phylogenetic analysis, MY-1 belonged to gC-genotype II composed of those Chinese strains. In mice, the 50% lethal dose (LD50) of MY-1 (103.0 TCID50) was almost the same as those of Yamagata-S81 and Bartha. The LD50 value of Begonia was 10≥4.5 TCID50. The mean survival periods of mice after infection with 104 TCID50 of MY-1, Yamagata-S81 and Bartha were 3.9 days, 2.3 days, and 8.0 days, respectively. The results suggested that the variant of Chinese PRV with slightly weaker pathogenicity than that of wild virulent viruses might be maintained in wild boars in Japan. Furthermore, we would like to propose that old Chinese strains, recent Chinese variant strains, and MY-1 should be grouped as an Asian type PRV.