Influenza D virus infection in China, 2022-2023

Influenza D virus (IDV) plays an important role in the bovine respiratory disease (BRD) complex. Its potential for the zoonotic transmission is of particular concern. In China, IDV has previously been identified in agricultural animals by molecular surveys with no live virus isolates reported. In this study, live IDVs were successfully isolated from cattle in China, which prompted us to further investigate the national prevalence, antigenic property, and infection biology of the virus. IDV RNA was detected in 11.1% (51/460) of cattle throughout the country in 2022-2023. Moreover, we conducted the first IDV serosurveillance in China, revealing a high seroprevalence (91.4%, 393/430) of IDV in cattle during the 2022-2023 winter season. Notably, all the 16 provinces from which cattle originated possessed seropositive animals, and 3 of them displayed the 100% IDV-seropositivity rate. In contrast, a very low seroprevalence of IDV was observed in pigs (3%, 3/100) and goats (1%, 1/100) during the same period of investigation. Furthermore, besides D/Yama2019 lineage-like IDVs, we discovered the D/660 lineage-like IDV in Chinese cattle, which has not been detected to date in Asia. Finally, the Chinese IDVs replicated robustly in diverse cell lines but less efficiently in the swine cell line. Considering the nationwide distribution, high seroprevalence, and appreciably genetic diversity, further studies are required to fully evaluate the risk of Chinese IDVs for both animal and human health in China, which can be evidently facilitated by IDV isolates reported in this study.