Sustained cross-species transmission of gammacoronavirus in wild birds revealed by viral characterization in China

<i>Gammacoronavirus</i> (γ-CoV) primarily infects poultry, wild birds, and marine mammals. The widespread distribution and circulation of γ-CoV in the ecological environment may lead to sustained transmission and economic loss. To better understand the diversity of γ-CoV in wild birds, we collected 482 wild-bird faecal samples from Yunnan, encompassing 14 bird species. We detected 12 γ-CoV-positive samples in five bird species, characterized five complete genomes-HNU5-1, HNU5-2, HNU5-3, HNU6-1, and HNU6-2-and proposed that these genomes represent two viral species. The HNU5 strains were derived from black-headed gull (<i>Chroicocephalus ridibundus</i>), while the HNU6 strains came from mallard (<i>Anas platyrhynchos</i>), and both of those were recombinant. The HNU5 strain exhibited the highest sequence identity (~95%) with a γ-CoV strain isolated from <i>Numenius phaeopus</i> (GenBank accession: PP845452). Similarly, the HNU6 strain showed 95% nucleotide identity with a γ-CoV strain (GenBank accession: PP845437) derived from <i>A. platyrhynchos</i>. Taxonomic analysis confirmed that HNU6s belong to the <i>Gammacoronavirus anatis</i> species, while HNU5s are attributed to a new species. Cross-species analysis revealed active host-switching events among γ-CoVs, indicating potential transmission of γ-CoVs from marine mammals to wild bird and from wild bird to poultry, and inter-wild bird and interpoultry transmission. In summary, we report five new γ-CoV strains in wild birds and outline the cross-species transmission of γ-CoVs. Our findings link γ-CoV hosts across different natural environments and provide new insights for exploring γ-CoVs.