Genotypes of canine distemper virus determined by analysis of the hemagglutinin genes of recent isolates from dogs in Japan

Canine distemper of domestic dogs is caused by canine distemper virus (CDV) , a member of the morbilliviruses. It has been a highly contagious disease of great veterinary importance for centuries, but for the last several deca des it has been controlled satisfactorily by modified live vaccines. In the 1990s, however, it was described that CDV strains genetically different fr om vaccine strains may have caused the disease in vaccinated dogs. The high est antigenic variation is found in the H protein. Therefore, in the presen t study, hemagglutinin (H) genes obtained from current vaccines and held is olates and amplified directly from clinical specimens were genetically anal yzed by restriction fragment length polymorphism assay and sequencing. Phyl ogenetic analysis of the ii-gene amino acid sequences revealed that at leas t two CDV genotypes are circulating among dogs in Japan; one is a genotype to which almost all Japanese CDV isolates belong and the other has not been previously described. Both are separate and independent from the other lin eages or genotypes of vaccine strains, as well as European and U.S. CDV iso lates. The results suggest that CDV has also evolved in Japan, and further studies will be needed for an evaluation and possible improvement of the ef ficacies of current CDV vaccines.