February 26, 2021

Study in China discovers milder African swine fever virus variants

A study published this week in China found new African swine fever (ASF) virus variants that are milder, which is less deadly but difficult to detect and get under control, Reuters reported.

The study by the Harbin Veterinary Research Institute under the Chinese Academy of Sciences is the second in February to report on natural mutations in ASF, which destroyed China's massive swine herd in 2018 and 2019 and continues to spread in the country.

The first study, which was published by the Military Veterinary Institute in Changchun, found ASF virus variants with a partial deletion of genes that were previously shown to safeguard swine from ASF when deleted. This initial study did not look into the virulence of the ASF variant.

The new study comes as China's swine industry is concerned over the virus' evolution with no approved vaccine available.

Sun Encheng and colleagues in the Life Sciences journal said the emergence of lower ASF virulent natural mutants makes it harder to detect ASF early and creates new challenges to control ASF.

They said the mutant virus result in a more delayed course with mid, chronic signs. It will continuously shed via the swine's oral and rectal routes

The study was based on sampling from seven provinces during the second half of 2020. The team discovered 22 isolates with mutations, then later tested four of those for virulence in swine.

Two of the isolates were found to be as deadly as the initial ASF virus spreading in China. But the remaining two showed lower virulence with symptoms that were partially lethal to non-lethal, depending on the doses given to the swine.

Some analysts projected that 20% of sows based in northern China have been affected by ASF this winter.

- Reuters