Sample collection
Under the permission and supervision of the Shanghai wildlife protection and management office, a total of 6,944 throat and anal swab samples of wild birds were collected in the Nanhui Dongtan wetland of Pudong (30°51′ to 31°06′ N, 121°50′ to 121°51′ E) and Jiuduansha Natural Reservation Zone (31°06′ to 31°14′ N, 121°46′ to 122°15′ E), Shanghai, China from 2016 to 2019. All wild birds were released after the samples were collected. The swabs were placed in a 5 ml cryopreserved tubes containing 2 ml virus carrier fluid and stored at -80℃ refrigerator for further analysis.