Pathogenesis and phylogenetic analyses of canine distemper virus strain 007Lm, a new isolate in dogs

The pathogenesis of a new isolate of canine distemper virus (CDV), strain 007Lm, was investigated from lymph node tissue by using Vero cells that express canine signalling lymphocyte activation molecules with a tag (Vero-DST) in dogs. Two CDV sero-negative Beagle dogs were inoculated intranasally and intraconjunctively with a virus suspension. Both infected dogs showed clinical signs of severe bloody diarrhea, conjunctivitis, ocular discharge, nasal discharge and coughing, lymphopenia, fever and weight loss. Titers of CDV-IgM and CDV-IgG in the blood were measured. CDV was detected by using reverse transcriptase-PCR and was recovered in swabs from one dog from 9 days and from the other dogs from 10 days after inoculation. Molecular and phylogenetic analyses of H and P genes showed that nucleotide and amino acid sequences of these genes of strain 007Lm after isolation in Vero-DST cells are identical to those of the original virus from fresh tissue and that strain 007Lm joins to the Asia 2 group cluster of CDV strains that is distinct from other clusters. These results indicate that (1) CDV strain 007Lm isolated in Vero-DST cells is virulent, (2) nucleotide and amino acid sequences of H and P genes of strain 007Lm do not change after isolation in Vero-DST cells compared with the original virus from fresh tissue and (3) strain 007Lm isolated from a vaccinated dog belongs to a cluster far from the vaccine strains in the phylogenetic trees of H and P genes.