A new form of African swine fever has been identified in Chinese pig farms. According to Reuters, industry insiders say that the disease was most likely caused by illegal vaccines, and serves as a fresh blow to the nation where the COVID-19 coronavirus was first identified. China is the world’s largest producer of pork.
Reuters reports that two new strains of African swine fever have infected over 1,000 sows on several farms run by New Hope Liuhe, which is China’s fourth-largest pork producer. Yan Zhichun, the company’s chief science officer, said that pigs fed by the company by contract farmers have also been infected.
Unlike the previously discovered African swine fever virus, the new strains are missing one or two genes, and do not kill the pigs. Instead, the disease causes a chronic condition that reduces the number of healthy piglets born. The company has performed a culling to prevent the spread of the disease.
As noted by Reuters, known infections remain limited, but the disease could slash pork output in China if further outbreaks occur. In 2018, swine fever decimated half of China’s 400 million-head pig herd. The price of pork remains at a record high due to the previous outbreak, and China has been under international pressure to increase its food security.
“I don’t know where they come from, but we find some mild field infections caused by some sort of gene-deleted viruses,” Yan said.
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, Yan said.
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.
Much like other diseases harmful to pigs, the newly discovered strains of African swine fever have the potential to contaminate meat outside of their immediate vicinity. Farmers believe that illegal vaccines have created accidental infections. Reuters says that the disease infects pigs that are fed on kitchen waste and is known to survive for months in some pork products.
China’s Ministry of Agriculture and Rural Affairs has issued at least three warnings against the use of illicit vaccines, warning farmers that they have the potential to carry severe side effects. Producers who are caught using the illegal vaccines may be charged with a criminal offense.
Last August, the Chinese government said that it would test pigs for different strains of the virus, as part of a nationwide investigation into the use of illicit vaccines. Although no studies have been published so far, reporting of recent outbreaks has been extensively covered up, according to Reuters, which produced a special report on the matter.
Scientists say that illegal vaccines have a risk of carrying the virus because even after the virus is weakened for the vaccine form so it does not cause serious illness, the disease itself can recover its virulence and spread. Reuters reports that a similar vaccine used in Spain in the 1960s caused chronic disease that complicated efforts to eradicate African swine fever for three decades. Since the outbreak, no nation has approved a vaccine for the disease.
According to Yan Zhichun, the newly discovered strains are “definitely man-made; this is not a natural strain.”