3.1 Serum epidemiological investigation
Serum samples were collected from 3 farms of breeding duck located in Shandong, Jiangsu and Anhui province, during December 2018 to March 2019. The sampled ducks were all vaccinated with N-DRV vaccine and antibody products, and detection of N-DRV antibody in the samples was performed by indirect ELISA. Of a total of 750 serum samples collected from breeding ducks, the number of N-DRV antibody positive samples was 734, and the positive rate was as high as 97.87%. Among the 119 duckling serum samples, the number of positive samples was 84, and the positive rate was 70.59%.
3.2 Clinical signs and pathological features