BEIJING (Reuters) – A new form of African swine fever identified on Chinese pig farms is most likely caused by illicit vaccines, say industry experts, a new blow to the world’s largest pork 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, as well as fattened pigs for the firm by contract farmers, said Yan Zhichun, the company’s chief scientist.
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 devastated China’s farms in 2018 and 2019, they cause a chronic condition that reduces the number of healthy piglets born, Yan said. for Reuters. In New Hope and many large producers, infected pigs are slaughtered to prevent the spread, making the disease fatal.
Although known infections are now limited, if the strains spread widely, they could reduce pork production to the top of the world’s consumer and producer; two years ago, swine fever wiped out half of China’s 400 million head of pigs. Pork prices are still 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 find some mild field infections caused by some kind of virus deleted by genes,” Yan said.
Wayne Johnson, a Beijing 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 discovered strains of the virus that lack both the MGF360 and CD2v genes, Yan said.
Research has shown that deleting MGF360 genes from African swine fever creates immunity. But the modified virus was not turned into a vaccine because it tended to later move back to a harmful state.
“You can sequence these things, these double deletions, and if it’s exactly the same as the one described in the lab, it’s too much of a coincidence, because you’ll never get the exact deletion,” said Lucilla Steinaa, chief scientist at International Livestock Nairobi Research Institute (ILRI).
There is no approved vaccine for African swine fever that is not harmful to humans. But many Chinese farmers struggling to protect their pigs have turned to unapproved products, industry experts and experts said. It is feared that 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.
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 severe side effects and that producers and users could be charged with a crime.
In August, the ministry said it would test pigs for various strains of the virus as part of a nationwide investigation into the illegal use of vaccines.
Any strains with genetic deletions could indicate that a vaccine has been used, he said. No results have been published so far on this issue, which is extremely sensitive for Beijing. Recent reports of outbreaks of African swine fever have been widely covered. For a link to the report, click here
STRANGES MADE BY MAN
After decades of research into a vaccine against the huge swine fever complex virus, researchers around the world are focusing on live virus vaccines – the only type that has shown any promise.
But such vaccines present higher risks, because even after the virus is weakened, so it does not cause serious disease, sometimes it can recover its virulence.
Such a vaccine used in Spain in the 1960s caused a chronic disease with swollen joints, skin lesions and respiratory problems in pigs, which 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 both the MGF360 genes and the deleted CD2v genes is being tested by the Harbin Veterinary Research Institute in China after showing promise.
Yan said he believes humans have reproduced the sequences of the virus strains studied, which have been published in the scientific literature, and that pigs injected with illicit vaccines based on them could infect others.
“It is certainly created by man; this is not a natural strain, “he said.
Neither Johnson nor Yan fully sequenced the new swine fever strains. Beijing strictly controls who is allowed to work with the virus, which can only be treated in laboratories with high biosecurity designations.
But several private companies have developed test kits that can verify specific genes.
GM Biotech, based in China’s central Hunan province, said in an online post last week that it has developed a test that identifies whether the pathogen is a virulent strain, a single-gene attenuated strain, or a single-gene attenuated strain. double gene.
The test helps pig producers because the new strains are “very difficult to detect in the initial stage of infection and have a longer incubation period after infection,” the company said.
The government has not said how used the illicit vaccines are or who produced them. But a “vast amount” of Chinese pigs were still vaccinated, Johnson said, echoed by many other experts.
In 2004-5, when H5 bird flu strains spread to Asia, Chinese laboratories produced several unauthorized vaccines against bird flu, said Mo Salman, a professor of veterinary medicine at Colorado State University who worked at animal health in Asia, growing fears that it could produce new dangerous variants.
“China’s current illegal vaccine (s) repeat history,” Salman said.
Reporting by Dominique Patton. Editing by Gerry Doyle