BEIJING (Reuters) – A new form of African swine fever diagnosed in Chinese pig farms is most likely caused by illegal vaccines, industry insiders say, another blow to the world’s largest pork producer, still recovering from a devastating epidemic of the virus.
Two new strains of African swine fever have infected more than 1,000 sows on various farms owned by New Hope Liuhe, China’s fourth-largest producer, and pigs fattened for the company by contract farmers, says Yan Zhichun, the Chief Science Company officer. .
Although the 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 Chinese farms in 2018 and 2019, they cause a chronic condition that reduces the number of healthy piglets. was born, Yan told Reuters. At New Hope, and at many major producers, infected pigs are culled to prevent spread, making the disease deadly.
While the known infections are now limited, if the strains spread widely they could reduce pork production at the world’s largest consumer and producer; two years ago, swine fever destroyed half of China’s 400 million swine herd. Pork prices are still at record levels and China is under pressure to strengthen food security during the COVID-19 pandemic.
“I don’t know where they come from, but we find some mild field infections caused by some kind of gene-deleted viruses,” said Yan.
Wayne Johnson, a Beijing veterinarian, said he was diagnosed with a chronic or less fatal form of the disease in pigs last year. The virus was missing certain genetic components known as the MGF360 genes. New Hope has found that strains of the virus lack 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 later tended to mutate back to a deleterious state.
“You can put these things, these double deletions, in order, and if it’s exactly the same as described in the lab, it’s too much of a coincidence because you’d never get that exact deletion,” said Lucilla Steinaa, chief scientist at the International. Livestock Research Institute (ILRI) in 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 insiders and experts said. They fear that illegal vaccines have caused accidental infections, which are now spreading.
The new strains could spread worldwide by infecting contaminated meat and pigs fed with 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 African swine fever vaccines, warning that these 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 for different strains of the virus as part of a nationwide investigation into illegal vaccine use.
Any strains with gene deletions could indicate that a vaccine has been used, he said. No findings have so far been published on this issue, which is very sensitive for Beijing. The report of the recent outbreaks of African swine fever has been extensively covered up. For a link to the report, click here
MAN-MADE STRAINS
After decades of research into producing a vaccine against the massive, complex swine fever virus, researchers around the world are turning to live virus vaccines – the only type that has shown any promise.
But such vaccines carry greater risks, because even after the virus has been weakened so that it doesn’t cause serious illness, it can sometimes restore its virulence.
One of those vaccines used in Spain in the 1960s caused a chronic disease with swollen joints, skin lesions and respiratory problems in pigs that hampered efforts to eradicate African swine fever over the next three decades. Since then, no country has approved a vaccine for the disease.
A vaccine with both MGF360 and CD2v genes deleted is undergoing trials by the Harbin Veterinary Research Institute in China after it showed promise.
Yan said he believes humans have replicated the sequences of the virus strains studied, which have been published in scientific literature, and that pigs injected with illegal vaccines based on them could infect others.
“It is definitely man-made; this is not a natural species, ”he said.
Neither Johnson nor Yan have fully sequenced the new swine fever strains. Beijing strictly controls who is allowed to work with the virus, which should only be handled in laboratories with a high biosafety rating.
But several private companies have developed test kits that can check for specific genes.
GM Biotech, based in China’s central Hunan province, said in an online post last week that it had developed a test that identifies whether the pathogen is a virulent strain, an attenuated strain with a single gene, or an attenuated strain with a double gene. .
The test helps pig farmers because the new strains “are very difficult to detect in the early stages of infection and have a longer incubation time after infection,” the company said.
The government has not said how widespread illegal vaccines are or who produced them. But a “massive amount” of pigs in China have nevertheless been vaccinated, Johnson said, a sentiment echoed by many other experts.
In 2004-5, as the H5 avian flu strains spread across Asia, Chinese labs produced several unauthorized live avian flu vaccines, said Mo Salman, a professor of veterinary medicine at Colorado State University who has worked on animal health in Asia. fears they could produce dangerous new variants.
“The current illegal vaccine (s) from ASF in China is repeating history,” Salman said.
Reporting by Dominique Patton. Editing by Gerry Doyle