2.1 Ethics statement
This study was performed according to the animal welfare guidelines of the World Organization for Animal Health, and animal sampling was strictly carried out in accordance with guidelines established by the Ethics of Animal Experiments of Northwest A&F University, Yangling, China. All protocols were approved by this committee (Permit Number: 2014BAD23B11). The field study did not include endangered or protected species. No specific permissions were required for the collection of samples because the samples were collected from public areas or non-protected areas.
2.2 Sample collection
In total, 571 serum samples were collected from healthy pigeons from 39 racing pigeon clubs between November 2016 and August 2019 in 11 provinces or municipalities of China, including Beijing, Hebei, Liaoning, Shanxi, Gansu, Qinghai, Shandong, Shaanxi, Xinjiang Uygur Autonomous Region, Ningxia Hui Autonomous Region and Inner Mongolia Autonomous Region. Moreover, 51 fatally diseased racing pigeons from 7 racing pigeon clubs in 5 provinces or municipalities were submitted to our laboratory at College of Veterinary Medicine, Northwest A&F University to determine the pathogen of the disease. The 0.2 g sections of internal organs (the heart, liver, spleen, lung, and intestine) were obtained during the postmortem examination of all mentioned dead pigeons. All samples were stored at −80°C before DNA extraction.