Experimental reproduction of canine influenza virus H3N8 infection in young puppies.

Canine influenza virus (CIV) subtype H3N8 has emerged as a new pathogen with sustained transmission in the dog population in the United States. In this study, we report the experimental induction of respiratory disease in dogs using three CIV field isolates. Young (14 to 15 weeks of age) CIV-seronegative pups were challenged with one of three CIV isolates and monitored for clinical signs of respiratory disease, nasal virus shedding, seroconversion, lung lesions, and virus isolation from the lower respiratory tract. The challenged pups developed clinical signs and lung lesions typical of influenza virus infection, shed virus in their nasal secretions for 7 to 8 days after challenge, and exhibited serum antibodies at 7 and 14 days after challenge. Lung tissues and tracheal swabs collected at 3 and 6 days after challenge exhibited active virus replication. These results demonstrate that CIV causes respiratory disease in dogs.