CHINESE scientists have discovered new strains of African swine fever  (ASF) that are milder but highly transmissible, complicating efforts to control the disease that’s roiled the world’s biggest pork market.

The new variants were found during a six-month surveillance of seven Chinese provinces last year, the Harbin Veterinary Research Institute said at a statement on Friday.

“The emergence of lower virulent natural mutants brings greater difficulty to early detection and poses new challenges for the control of ASF,” a team of scientists from the Harbin institute wrote in a paper last week.

Fresh outbreaks of African swine fever, coupled with other lethal pig illnesses such as foot-and-mouth disease and porcine epidemic diarrhea, have sparked doubts over the recovery of China’s hog herds. The top pork consumer saw pig numbers slashed by about half and prices of the meat skyrocket after swine fever was first discovered in China in 2018.

With no timeline yet on commercial vaccines against swine fever, controlling the disease still relies on early diagnosis and culling infected animals. The new mutant strains will make it even harder to keep a lid on outbreaks as they will be difficult to detect while the virus is continuously “shed via the oral and rectal routes,” according to the Harbin newspaper.

The team has found and isolated 22 viruses, characterized as genotype II African swine fever, based on 3,660 samples collected from farms and slaughterhouses in the provinces of Heilongjiang, Jilin, Liaoning, Shanxi, Inner Mongolia, Hebei, and Hubei between June to December, 2020. — Bloomberg