By NewsDesk  @bactiman63

A new study published in the journal, Science China Life Sciences, Chinese researchers with the Harbin Veterinary Research Institute in Heilongjiang report the discovery of new strains of African swine fever that are milder but highly transmissible.

According to a statement from Harbin Veterinary Research Institute (computer translated):

Image/Robert Herriman

In 2020, the National African Swine Fever Specialty Laboratory of Harbin Institute of Veterinary Medicine of the Chinese Academy of Agricultural Sciences found that African swine fever genotype II with low fatality rate appeared in some provinces and regions of my country during the epidemiological surveillance and etiology research of African swine fever. Variant epidemic strains. The related research paper “Emergence and prevalence of naturally occurring lower virulent African swine fever viruses in domestic pigs in China in 2020” was published online in “SCIENCE CHINA Life Sciences” on February 26, 2021.

At present, at least 24 genotypes of African swine fever virus have been identified worldwide. Among them, genotype II is the main prevalent in Asia. Currently, there is no commercial vaccine or effective treatment for African swine fever. Early diagnosis and culling of infected pigs are the main strategies for prevention and control. Therefore, carrying out epidemiological surveillance and research on the genome variation, biological phenotype and pathogenicity of epidemic strains is of key guiding significance for the prevention and control of African swine fever.

The National African Swine Fever Professional Laboratory isolated and identified my country’s first African swine fever virus HLJ/18 in 2018. From June to December 2020, the research team of this laboratory carried out more systematic African swine studies in some provinces and regions in my country. Epidemiological surveillance of pestivirus, 22 strains of African swine fever genotype II were isolated. Compared with the earliest isolate HLJ/18, the genome sequence of the isolate in 2020 has changed to varying degrees, including nucleotide mutations, deletions, insertions or short fragment replacements. Among them, the EP402R genes of 11 strains showed four different types of natural nucleotide mutations or deletions, resulting in CD2v protein coding defects and loss of HAD phenotype (non-HAD). Four representative strains of viruses were selected for animal regression tests. Among them, two strains with HAD phenotype were similar in pathogenicity to HLJ/18, and showed typical high lethality.

It is worth noting that the two non-HAD phenotype isolates showed low virulence, but still showed obvious residual virulence. High-dose infection can cause subacute and chronic disease courses, and some deaths. Infected pigs; low-dose vaccination mainly causes non-fatal persistent infections, as well as subacute or chronic disease courses. Both strains of non-HAD viruses have strong horizontal transmission ability, especially HeB/Q3/20 performance is more prominent.

This study found that there are at least four natural variants of low-fatality gene type II in the field in my country. Although the pathogenicity is significantly lower than that of the typical virulent strains, it still shows obvious residual virulence and has a strong horizontal transmission ability; its clinical manifestations have a certain degree of concealment, and it is likely to have been prevalent in field pig herds. Continuous infection, chronic disease and even death have brought great obstacles to the early diagnosis of African swine fever, and brought new challenges to the prevention and control of African swine fever in my country. We must attach great importance to it and formulate and adopt countermeasures as soon as possible.


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