BEIJING (Reuters) – A new form of African swine fever identified on Chinese pig farms is likely to be caused by illicit vaccines, according to industry experts, a new blow to the world’s largest pig producer, which is still recovers from a devastating epidemic of the virus.
Two new strains of African swine fever have infected more than 1,000 sows on several farms owned by New Hope Liuhe, China’s fourth-largest producer, in addition to pigs that have been fattened by the company by contract farmers, said Yan Zhichun, chief company scientist.
Although strains, which lack one or two key genes present in the wild African swine fever virus, do not 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, Yan told Reuters. In New Hope and many large producers, infected pigs are slaughtered to prevent the spread, making the disease effectively deadly.
Although known infections are limited now, if the strains spread widely, they could reduce pig production in the world’s largest consumer and producer; two years ago, swine fever wiped out half of China’s 400 million head herd of pigs. Pork prices remain at record levels and China is under pressure to strengthen food security amid the COVID-19 pandemic.
“I don’t know where they come from, but we do find some mild field infections caused by some kind of gene suppressed virus,” Yan said.
Wayne Johnson, a Beijing-based veterinarian, said last year he diagnosed a chronic or less lethal form of the disease in pigs. The virus did not have certain genetic components, known as the MGF360 gene. New Hope has found strains of the virus that are missing from both the MGF360 and CD2v genes, Yan said.
Research has shown that suppressing some MGF360 genes from African swine fever creates immunity. But the modified virus did not become a vaccine because it tends to subsequently mutate to a harmful state.
“You can sequence these things, these double deletions, and if it’s exactly the same as described in the lab, it’s too coincidental, because you’ll never get that exact deletion,” said Lucilla Steinaa, senior scientist at the International Livestock Research Institute (ILRI) of Nairobi.
There is no approved vaccine against African swine fever that is not harmful to humans. But many Chinese farmers struggling to protect their pigs have resorted to unapproved products, industry experts and experts said. They fear that illicit vaccines have created accidental infections, which are now spreading.
New strains could proliferate globally through contaminated meat, infecting pigs that feed on kitchen waste. The virus is known to survive for months in some pork products.
China’s Ministry of Agriculture and Rural Affairs did not respond to two requests for comment.
But it has issued at least three warnings against the use of unauthorized vaccines against African swine fever, warning that they could have serious side effects and that producers and users could be charged with a criminal offense.
In August, the ministry said it would test pigs from different strains of the virus as part of a nationwide investigation into the illegal use of vaccines.
All strains with gene suppression could indicate that a vaccine had been used, he said. No conclusions have been published so far on the issue, which is very sensitive for Beijing. Reporting of recent outbreaks of African swine fever was widely covered. Click here for a link to the report
CUTS MADE BY MAN
After decades of research to produce a vaccine against the huge and complex swine fever virus, researchers around the world are focusing on live virus vaccines, the only type that has shown any promise.
But these vaccines carry higher risks, because even after the virus weakens, so that it does not cause serious illness, it can sometimes regain its virulence.
One of these vaccines used in Spain in the 1960s caused a chronic disease with swollen joints, skin lesions and respiratory problems in pigs that complicated efforts to eradicate African swine fever over the next three decades. Since then, no nation has approved a vaccine against the disease.
A vaccine with deleted MGF360 and CD2v genes is being tested by China’s Harbin Veterinary Research Institute after promising.
Yan said he believes people have replicated the virus strain sequences being studied, which have been published in the scientific literature, and that pigs injected with illicit vaccines based on them could infect others.
“It’s definitely artificial; it’s not a natural strain, ”he said.
Neither Johnson nor Yan have completely sequenced the new swine fever strains. Beijing strictly controls who can work with the virus, which can only be handled in laboratories with high biosecurity designations.
But several private companies have developed test kits that can check for specific genes.
GM Biotech, based in central Hunan province in China, said last week in an online message that it had developed a test that identifies whether the pathogen is a virulent strain, an attenuated strain removed by a single gene, or an attenuated strain removed by double gene.
The test helps pig producers because new strains are “very difficult to detect in the early stages of infection and have a longer incubation period after infection,” the company said.
The government has not said to what extent the illicit vaccines are used or who produced them. However, a “large number” of pigs in China have been vaccinated, Johnson said, a sentiment echoed by many other experts.
In 2004-5, when H5 bird flu strains spread across Asia, Chinese labs produced several unauthorized live vaccines against bird flu, said Mo Salman, a professor of veterinary medicine at Colorado State University. who has worked in animal health in Asia. fears that they may produce new dangerous variants.
“Current ASF illegal vaccines in China repeat history,” Salman said.
Report by Dominique Patton. Edited by Gerry Doyle