Co-circulation of coronavirus and avian influenza virus in wild birds in Shanghai (2020-2021)

Co-infection of SARS-CoV-2 and influenza viruses has been reported worldwide in humans. Wild birds are natural reservoir hosts for coronaviruses (CoVs) and avian influenza viruses (AIVs). It is unknown whether co-infection with these two types of viruses occurs in wild birds. In this study, the prevalence of co-infection with CoV and AIV in wild birds in Shanghai, China during 2020-2021 was investigated by detecting these viruses in cloacal, tracheal, and faecal samples. Results showed that the overall rate of samples positive for both CoV and AIV was 3.3% (82/2510; 95% confidence interval [CI]: 2.6%-4.0%), and that was mainly from Anseriformes. In CoV-positive samples, 38.9% (82/211; 95% CI: 32.5%-45.6%) of them had both CoVs and AIVs, whereas only 26.9% (82/305; 95% CI: 22.2%-32.1%) of AIV-positive samples had both CoVs and AIVs. These results suggest that CoV infection in wild birds renders them more susceptible to AIV infection. Phylogenetic analysis based on partial RNA-dependent RNA polymerase (RdRp) gene sequences of CoVs revealed that gamma-CoVs mainly cluster with duck CoVs and that delta-CoVs are more diversified and cluster with those of various wild birds. Continual surveillance is necessity to monitor the transmission and evolution of co-infection of these two types of viruses in their natural hosts.