Limited adaptation of chimeric H9N2 viruses containing internal genes from bat influenza viruses in chickens

Influenza virus-like sequences of H17N10 and H18N11 were identified in bats, despite there has been no live virus isolated. The genetic analysis indicated that they have distinct but relatively close evolutionary relationships to known influenza A viruses. However, the infectivity and adaptation of bat influenza viruses in avian species remain unclear. In this study, two modified bat influenza viruses cH9cN2/H17 and cH9cN2/H18 containing HA and NA coding regions replaced with those of H9N2 influenza A virus were generated in the background of the H17N10 or H18N11 viruses. These two modified viruses replicated less efficiently than wild type H9N2 virus in cultured chicken cells. The mini-genome assay showed that viral ribonucleoproteins (vRNPs) of H9N2 has significantly higher polymerase activity than that of bat influenza viruses in avian cells. In chicken study, compared with H9N2 virus, which replicated and transmitted efficiently in chickens, the cH9cN2/H17 and cH9cN2/H18 viruses only replicated in chicken tracheas with lower titers. Pathological examination showed that the H9N2 caused severer lesions in lung and trachea than the modified bat influenza viruses. Notably, the cH9cN2/H18 transmitted among chickens, but not cH9cN2/H17, and chicken IFN-β antagonism results showed that H18N11 NS1 protein inhibited chicken IFN-β response more efficiently than H17N10 NS1 protein in avian cells. Taken together, our data indicated that the internal genes of bat influenza viruses adapted poorly to chickens, while the internal genes of H18N11 seemed to adapt to chickens better than H17N10.