Long-term surveillance of avian avulavirus in wild birds in China from 2003 to 2020

Avian avulavirus (AAVV) is a significant pathogen affecting avian species, but research on its prevalence in wild birds in China has been relatively limited. In this study, active surveillance for AAVV was conducted in wild birds in China from 2003 to 2020. A total of 124,882 samples were collected from 26 provinces, and 220 AAVV-positive samples were identified, encompassing various serotypes including AAVV-1, -4, -6, -8, -9, -13, and -16. Notably, AAVV-9 isolates were reported for the first time in China through this study. Detailed genetic analysis of 148 representative strains revealed that 26 of them exhibited a polybasic amino acid residue at the F gene cleavage site, a molecular marker associated with virulent AAVV strains in chickens. The geographical isolation between the Old and New Worlds has led to the independent evolution of AAVVs in each region, resulting in distinct Eurasian and North American lineages. Our findings predominantly aligned with the Eurasian lineage. However, repeated detections of AAVVs of North American origin in wild birds in China suggests potential viral dispersal between North America and China, which warrants further investigation. Furthermore, geographical reconstruction of AAVV-4 occurrence indicated a possible transmission route from Europe to East Asia. The origin of AAVV-4 remains uncertain due to limited sequence data, underscoring the need for expanded surveillance and highlight the necessity for sustained, long-term epidemiological surveillance efforts.