Pathogenicity of H5N8 avian influenza virus in chickens and in duck breeds and the role of MX1 and IFN-α in infection outcome and transmission to contact birds.

This study examined the pathogenicity, immunogenicity, and transmission potential of the H5N8 HPAI clade 2.3.4.4b virus in three breeds of ducks and in broiler chickens. Chickens, Muscovy, Pekin, and Mallard ducks (n = 10) received a dose of 6 log EID of HPAIV H5N8 directly. Nine contact chickens were introduced to each group on the day of infection. All infected chickens died, with MDT of 7.6 days. Muscovy and Pekin ducks died by 11.1% and 10%, respectively, with MDTs of 7 and 6 days. No Mallards died but showed more severe clinical disease than Pekin ducks. Mallards had the highest MX1 gene expression in the lung and spleen and IFN-α in the spleen. MX1 expression levels were lower in the spleen and lung of Pekin ducks, in the spleen of chickens and in the lung of Muscovy ducks than in noninfected controls. However, viral shedding was higher in ducks than in chickens and was highest in Mallards. 66.7% of chickens placed in contact with infected chickens died and 77.8% of in-contact chickens to infected three duck breeds died. In conclusion, there was a diversity in sensitivity and immunogenicity for HPAIV H5N8 among duck breeds, resulting in diverse infection outcomes and transmissibility to contacts. This study provides duck/chicken interface models for HPAIV transmission to poultry.