Phylogenetic and sequence analysis of the co-circulating lineages in the canine distemper virus complexity from Northern Vietnam (2017-2023).

Morbillivirus canis, commonly known as Canine distemper virus (CDV), causes Canine distemper (CD) in carnivore species across the world and spreads via cross-species transmission between domestic and wildlife canids, non-canid carnivores, and omnivores. We report on the Asia-4 lineage of CDV previously documented in Thailand and China, which has emerged for the first time in northern Vietnam since 2017. The phylogenetic analysis of 121 complete nucleotide CDS (coding sequence) of the hemagglutinin (H) gene, including 20 from this study, and 101 reference strains from all 19 lineages of CDVs revealed that the Asia-4 lineage co-circulated with the Asia-1 in Vietnam. The evolutionary distances (ED) or genetic distances between the Vietnamese and typical Asia-4 strains was low, substantially distinguishing them from other lineages. The immunodominant epitopes, host-switching, and glycosylation sites in Asia-4 viruses have several site alterations, providing fair insights into the effectiveness of the America-1-based vaccine. In addition to Thailand, China, Russia, and Mongolia, the Asia-4 lineage has appeared in northern Vietnam. Whether via canine and pet or wild animal trade/border crossing trafficking to Vietnam, remains to be studied. Our findings contribute to a better understanding of CDV molecular epidemiology and the suitable application of lineage-antigenic matching vaccines, as well as the complicated co-circulation of multiple-lineage strains in Vietnam.