The biological characteristics and infection dynamics of a novel H3N2 canine influenza virus genotype in beagles.

BACKGROUND: The canine influenza virus (CIV) outbreak has garnered considerable attention as it poses a significant threat to dog health. During the H3N2 CIV evolution in beagles, the virus formed a new clade after 2019 and gradually became more adaptable to other mammals. Therefore, successfully elucidating the biological characteristics and constructing a canine influenza infection model is required for CIV characterization. METHODS: We performed genetic analyses to examine the biological characteristics and infection dynamics of CIV. RESULTS: The genotype of our H3N2 CIV strain (from 2019 in Shanghai) belonged to the 5.1 clade, which is now prevalent in China. Using MDCK cells, we investigated viral cytopathic effects. Virus size and morphology were observed using transmission electron microscopy. Beagles were also infected with 104, 105, and 106 50% egg-infectious doses (EID50). When compared with the other groups, the 106 EID50 group showed the most obvious clinical symptoms, the highest virus titers, and typical lung pathological changes. Our results suggested that the other two treatments caused mild clinical manifestations and pathological changes. Subsequently, CIV distribution in the 106 EID50 group was detected by hematoxylin and eosin (H&E) and immunofluorescence (IF) staining, which indicated that CIV primarily infected the lungs. CONCLUSIONS: The framework established in this study will guide further CIV prevention strategies.

Epidemiological survey and genetic evolution of H3N2 subtype influenza viruses from stray dogs in Shanghai, China.

An avian-origin canine influenza virus (CIV) has recently emerged in dogs and is spreading in China. Given that humans have frequent contact with dogs, this has prompted an increased emphasis on biosafety. In this study, we collected 693 nasal swab samples and 800 blood samples from stray dogs in animal shelters to survey canine influenza epidemiology and characterize the evolution of CIV H3N2 in Shanghai. We tested samples for canine influenza antibodies and canine influenza RNA in January-May, 2019, and the results showed that the positive rate was 17.62% by ELISA, 15.75% by microneutralization (MN) assay, and 18.51% by real time RT-PCR, respectively. We also performed phylogenetic and genomic analysis on six H3N2 CIV isolates. The H3N2 viruses which prevailed in Shanghai originated from Beijing and Jiangsu isolates. Phylogenetic analysis showed that the sequences of CIV isolates have multiple amino acid antigenic drifts, deletions, and substitutions. The time of the most recent common ancestor (TMRCA) of HA and NA was 2004 and 2005, respectively. Notably, the substitution, 146S, in hemagglutinin and the deletion in the neuraminidase (NA) stalk region we found in this study warrant attention because they have frequently been identified in human influenza viruses. The potential adaptation of this CIV H3N2 clade to mammals and its public health threat should be further evaluated.