The national surveillance study of grass carp reovirus in China reveals the spatial-temporal characteristics and potential risks

Abstract Grass Carp Reovirus (GCRV) causes serious hemorrhagic disease in fingerling and yearling grass carp and is listed as a Class II animal disease by the Ministry of Agriculture and Rural Affairs of China. To clarify the epidemic characteristics of GCRV in China, this study monitored grass carp hemorrhagic disease in China from 2017 to 2020. A total of 108 farms were positive for GCRV, accounting for 10.2% of the monitored farms. Guangxi, Guangdong, Tianjin, Hubei, and Jilin Provinces were the highest GCRV-positive regions, which accounted for 39.8% of China's grass carp production. The GCRV positive rate was not consistent during 2017–2020, with the highest rate in 2020 and the lowest rate in 2019. GCRV was not detected during every year of the study, except in Guangdong, Guangxi, and Hubei. Moreover, only 17 farms recorded GCRV-positive cases for 2 consecutive years, and farms that introduced fingerlings during the culture period and closed the cultivation grounds had a higher risk of GCRV, suggesting that GCRV is more likely to be transmitted from other farms rather than from previous years. Our results suggest that improved quarantine when fingerlings are introduced may block the continuous transmission of GCRV.