1. National Research Center for Veterinary Medicine, High-Tech District, Luoyang, People's Republic of China
2. Veterinary Diagnosis Center and OIE Porcine Reproductive and Respiratory Syndrome Laboratory, China Animal Disease Control Center, Chaoyang District, Beijing, People's Republic of China
3. College of Animal Science and Veterinary Medicine, Henan Agricultural University, Zhengzhou, People's Republic of China