Protective efficacy and immunogenicity of an inactivated avian-origin H3N2 canine influenza vaccine in dogs challenged with the virulent virus

Abstract

Transmission of avian-origin influenza A virus (H3N2) to dogs had been reported and since then the H3N2 virus infection across South Korea has been occurred repeatedly in the country's animal clinics and kennels. Dog-to-dog transmission of the virus had also been experimentally demonstrated by direct contact. In this study, immunogenicity and protective efficacy against challenge exposure of the formalin-inactivated H3N2 influenza virus vaccine with a synthetic polymer adjuvant was investigated in dogs. The beagle puppies received two inactivated vaccine injections intramuscularly 2 weeks apart. Serological investigation by a hemagglutination inhibition (HI) test and an ELISA assay indicated that a significant increase in antibody titer was displayed 2 weeks after the second vaccination. Clinical signs, virus shedding and histopathological lesions in the lungs were exhibited in unvaccinated beagle puppies directly challenged through an intranasal route with the virus 2 weeks after the second vaccination. However, the vaccinated animals did not show any clinical signs and showed milder pathological lung lesions and shorter shedding duration with lower loads than controls'. These results indicated that the synthetic polymer-adjuvant avian-origin canine influenza virus (CIV) vaccine had produced antibody response and protection from avian-origin CIV challenge in dogs.