Chinese scientists have confirmed that milder mutations of African Swine Fever virus (ASFv) are going around in China.
The conclusions were drawn by scientists from the Harbin Veterinary Research Institute. The study was published in the journal Life Sciences, a publication by Science China and follows earlier reports about ASFv mutations emerging in China.
In their article, the researchers wrote: “The emergence of lower virulent natural mutants brings greater difficulty to the early diagnosis of ASF and creates new challenges for ASFv control.” They added, “Considering the huge population of pigs in China and an endemic period of more than 2 years, it is not surprising to find complex genetic diversity among the field ASFvs in China.”
The scientists did a surveillance in 7 Chinese provinces from June to December 2020. They took 3,660 samples from farms, slaughterhouses and disposal plants in Hebei, Heilongjiang, Hubei, Inner Mongolia, Jilin, Liaoning and Shanxi provinces. They isolated and characterised 22 viruses belonging to the genotype II ASFv. All 22 had mutations, deletions or replacements in comparison to “HLJ/18”, the earliest isolate in China.
The researchers wrote: “11 isolates had 4 different types of natural mutations or deletion in the EP402R gene and displayed a non-haemadsorbing (non-HAD) phenotype. Another 4 isolates were tested for virulence in pigs; 2 were found to be as highly lethal as HLJ/18. However, 2 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.”
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The researchers also noted that no commercial vaccines are available for ASFv. They said, “Therefore, control of the disease relies on the rapid diagnosis and culling of infected animals. The emergence of the non-HAD mutants will cause more problems and pose bigger challenge for the ASF control in China since they cause a much more delayed course, and mild, chronic disease signs, while being continuously shed via the oral and rectal routes.”
The Harbin institute has been working on an ASF vaccine based on the deletion of 7 genes. The scientists aim to figure out whether or not their vaccine provides protection against the newly discovered lower virulent strains.
A few weeks ago, China-based veterinarian Dr E. Wayne Johnson already stated that a mutated version of ASFv had found its way into some Chinese barns, most probably caused by the use of improper bootleg vaccines. In his observations, the MGF360 gene had changed – this gene the Harbin study did not speak of.
The Harbin publication follows an earlier study from the Military Veterinary Institute in Changchun. According press agency Reuters, that study reported finding a virus that had a partial deletion of genes, previously shown to protect pigs against the ASF when deleted.
The research paper was authored by 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, Fang Li, Renqiang Liu, Yuntao Guan, Dongming Zhao and Zhigao Bu, Harbin Veterinary Research Institute, China; and Xuewu Yu, Inner Mongolia University for the Nationalities, Tongliao, China.