Pathobiological Characteristics Of H3N2Canine Influenza Virus Isolated From Jiangsu

Canine influenza virus (CIV) is an emerging pathogen that causes acute respiratory disease in dogs, which poses a serious threat to dog health. Since dogs are considered as companion animals, CIV infection causes considerable concerns for public health. Most of CIV strains circulating in Asia in recent years are avian-origin CIVs, some of which could cause severe respiratory diseases in dogs. Currently, the majority of CIV isolates in China is H3N2subtype of avian-origin. Our previous study showed that A/canine/Jiangsu/06/2010(H3N2)(CIV06), which is isolated in Jiangsu Province of China and is avian-origin, could cause extrapulmonary infection in mice and discharged virus through digestive tract, suggesting that CIV06possesses special pathobiological characteristics different from the previous strains.According to the results of pathogenicity study in mice, animal regression experiment was carried out to investigate the pathogenicity of CIV06. Nine dogs were inoculated intranasally with10795of50%egg infectious dose (EID50) of the virus. Dogs in control group were inoculated with the same amount sterilized PBS. The onset of clinical signs and virus shedding was observed on day1post-infection (p.i.). The peak clinical score occurred between days4and6p.i. The experimentally infected dogs were found to shed virus not only via the respiratory tract but also via the digestive tract. Viral RNA could be detected in multiple organs including the trachea, lung, liver, spleen, kidney, brain and duodenum. All the sampled organs from infected dogs showed significant lesions and viral antigen staining. The results differed from those reports using previous CIV strains, and the Chinese isolate could induce extrapulmonary infection and cause extensive lesions in dogs.In order to investigate whether CIV06can re-infect birds, or be transmitted from infected birds to other healthy birds, the chickens were divided into3groups including infection group (n=20), contact transmission group (n=4) and control group (n=4). Twenty chickens in infection group were inoculated intranasally with10695EID50of the virus in0.1ml PBS. The other two groups were received the same volume of PBS via intranasal route. None clinical signs were observed in experimentally infection group, contact transmission group and control group throughout the experiment. Virus shedding was observed on day1-9post-infection (p.i.) in pharyngeal swabs and no virus was detected in the cloacal swabs. Viral RNA could be detected in trachea, lung, serum, cardiac muscle, breast muscle and spleen. Only lung and spleen from infected chickens showed pathological changes by H&E stains, but all the tissues described above showed viral antigen staining by immunohistochemistry. Moreover, seroconversion was observed in the samples from the inoculated chickens by performing the HI test. These findings showed that the CIV06could experimentally infect chickens by intranasal inoculation, but the chickens infected with CIV could not constitute a source of CIV infection in chicken.In conclusion, CIV06of avian-origin can cause stronger pathogenicity and systemic infection in dogs, while the chickens showed no obvious pathogenicity. This study lays a foundation for further study of canine influenza virus pathogenesis.