Different outcomes of infection of chickens and ducks with a duck-origin H9N2 influenza A virus.

As the major aquatic and terrestrial hosts for avian influenza viruses (AIVs), ducks and chickens play a critical role in the evolution and spread of the H9N2 virus. However, the outcomes of infection of ducks and chickens with the H9N2 virus are not sufficiently documented. In this study, we compared the outcomes of infection of chickens and Peking ducks with a duck-origin H9N2 virus. The results showed that this virus caused more pronounced clinical signs and histological lesions in chickens. As for the virus shedding, chickens shed more virus in the trachea and less virus in the cloaca in levels of interferon (IFN) γ were found in the trachea of ducks compared with chickens, while comparison with ducks. As for cytokines, namely IFNs and interleukins (IL), higher higher levels of IFN-β, IFN-γ, IL-1β, and IL-6 were observed in the ileum of chickens compared with ducks. Eventually, serum hemagglutination-inhibition (HI) antibody titers were higher in chickens than in ducks. Taken together, ducks and chickens use different strategies in response to the H9N2 virus infection in tissues representing main replication sites of low-pathogenic AIVs. Given the different outcomes of the H9N2 virus infection in ducks and chickens, different measures should be taken in vaccination and treatment.