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