Encheng Sun,Zhenjiang Zhang,Zilong Wang,Xijun He,Xianfeng Zhang,Lulu Wang,Wenqing Wang, Lianyu Huang,Fei Xi,Haoyue Huangfu,Ghebremedhin Tsegay,Hong Huo,Jianhong Sun,Zhijun Tian,Wei Xia,Xuewu Yu,Fang Li,Renqiang Liu,Yuntao Guan,Dongming Zhao,Zhigao Bu

Sci China Life Sci.2021 Feb 26.doi: 10.1007/s11427-021-1904-4. Online ahead of print.

Abstract

African swine fever virus (ASFV) has been circulating in China for more than two years, and it is not clear whether the biological properties of the virus have changed. Here, we report on our surveillance of ASFVs in seven provinces of China, from June to December, 2020. A total of 22 viruses were isolated and characterized as genotype II ASFVs, with mutations, deletions, insertions, or short-fragment replacement occurring in all isolates compared with Pig/HLJ/2018 (HLJ/18), the earliest isolate in China. Eleven isolates had four different types of natural mutations or deletion in the EP402R gene and displayed a non-hemadsorbing (non-HAD) phenotype. Four isolates were tested for virulence in pigs; two were found to be as highly lethal as HLJ/18. However, two non-HAD isolates showed lower virulence but were highly transmissible; infection with 106 TCID50 dose was partially lethal and caused acute or sub-acute disease, whereas 103 TCID50 dose caused non-lethal, sub-acute or chronic disease, and persistent infection. The emergence of lower virulent natural mutants brings greater difficulty to the early diagnosis of ASF and creates new challenges for ASFV control.

Keywords: African swine fever virus; lower virulent; natural mutant; non-hemadsorbing.