A staff member cleans a pigsty at Jinchuan pig farm of Jiangxi Zhengbang breeding Co. Ltd. in Xingan County, east China's Jiangxi Province. Photo: Xinhua

 A research team from the Chinese Academy of Agricultural Sciences has found natural mutation in African Swine Fever (ASF) genotype II virus appearing in some provinces of China, but the epidemic strain of ASF showed low lethality. 

The study, which was conducted by an ASF lab from the Harbin Veterinary Research Institute in Northeast China's Heilongjiang Province, found that there are at least four natural variants of ASF genotype II with low lethality.

The clinical manifestations of the variant are relatively concealed, and it is likely to have been prevalent among pigs in the fields, causing persistent infections, chronic course of diseases and even deaths, according to the findings. 

"The concealed manifestations of the variant will increase difficulty of early diagnosis of ASF and bring challenges to the prevention and control of the disease in China, so great attention must be paid to it and countermeasures should be formulated and adopted soon," said Zhao Dongming, a research fellow at the institute.

The study was published in Science China Life Sciences, a Chinese academic journal for life sciences. 

ASF is common in China and happens almost every year in the country, Yang Zhanqiu, a deputy director of the pathogen biology department at Wuhan University, told the Global Times on Tuesday, noting that ASF usually has a high fatality rate for pigs. 

At least 24 genotypes of ASF virus have been identified worldwide, and the most prevalent one in Asia is genotype II. 

There are currently no commercial vaccines or effective treatment for ASF. Early diagnosis and culling of infected pigs is the main measure used to control the disease, which makes the epidemiological monitoring and the study of genomic variation of epidemic strains very important, said a statement from the veterinary research institute.

The research team carried out systematic surveillance of ASF virus in some provinces and regions of China from June to December 2020, isolating 22  genotype II ASF epidemic strains.

In 2019, 63 cases of ASF were reported across the country with 390,000 pigs culled, according to statistic of the Ministry of Agriculture and Rural Affairs.