Comparative pathogenicity of wild-type and E3-deleted canine adenovirus type 2 in experimental canine infections

Canine adenovirus type 2 (CAdV-2) is a major etiological agent of canine infectious respiratory disease (CIRD), responsible for acute laryngotracheitis and bronchopneumonia. In this study, we isolated and characterized three CAdV-2 strains from clinical cases in Guangxi, China. Among these, we identified a novel E3 gene variant (designated GXNN01) featuring a 9-nucleotide deletion, resulting in a 3-amino acid truncation. To access the pathogenicity of these strains, we conducted experimental infections in a canine model. All infected dogs developed transient fever (39.2-39.8 °C) and exhibited characteristic respiratory symptoms, including coughing and nasal discharge. High viral loads were detected in the tracheal and lungs at 4 days post-infection. Histopathological examination revealed acute tracheobronchitis and focal alveolar damage, consistent with the pathological manifestations of CAdV-2 infection. Notably, the E3-mutated strain demonstrated virulence comparable to that of wild-type isolates, suggesting functional redundancy in the E3 genomic region. These findings significantly enhance our understanding of CAdV-2 pathogenesis, provide valuable insights for vaccine development, and underscore the importance of continuous surveillance to track its global spread and impact on canine health.