A new form of the swine flu fever has been identified in Chinese pig farms is most likely caused by illicit vaccines, experts suggest.
Two strains of the African swine fever have infected more than 1,000 sows on several farms owned by New Hope Liuhe, China’s fourth-largest producer, as well as pigs being fattened for the firm by contract farmers, said Yan Zhichun, the company’s chief science officer.
Though the strains, which are missing one or two key genes present in the wild African swine fever virus, don’t kill pigs like the disease that ravaged China’s farms in 2018 and 2019, they cause a chronic condition that reduces the number of healthy piglets born.
Large producted cull the infected pigs to prevent the spread. Although the known infections are limited now, if the strains spread widely, they could slash pork output in the world’s top consumer and producer.
In 2018, swine fever wiped out half of China’s 400 million-head pig herd. Pork prices are still at record levels and China is under pressure to strengthen food security amid the COVID-19 pandemic.
Wayne Johnson, a Beijing-based veterinarian, said he diagnosed a chronic, or less-lethal, form of the disease in pigs last year. The virus lacked certain genetic components, known as the MGF360 genes. New Hope has found strains of the virus missing both the MGF360 genes and the CD2v genes.
Research has shown that deleting some MGF360 genes from African swine fever creates immunity. But the modified virus was not developed into a vaccine because it tended to later mutate back to a harmful state.
There is no approved vaccine for African swine fever, which is not harmful to humans. But many Chinese farmers struggling to protect their pigs have resorted to unapproved products, industry insiders and experts said. They fear illicit vaccines have created accidental infections, which are now spreading.
The new strains could proliferate globally through contaminated meat, infecting pigs that are fed on kitchen waste. The virus is known to survive for months in some pork products.