New strains of swine fever in China indicate unlicensed vaccines

BEIJING (Reuters) – A new form of African swine fever identified in Chinese pig farms is most likely caused by illicit vaccines, industry insiders say, a further blow to the world’s largest pork producer, who is still recovering from a devastating outbreak of the virus.

Two new strains of African swine fever have infected more than 1,000 sows at several farms owned by New Hope Liuhe, China’s fourth largest producer, as well as pigs fattened for the company by contract farmers, said Yan Zhichun, scientific director of the company. .

Although the strains, which lack one or two key genes found in the wild African swine fever virus, don’t kill pigs like the disease that plagued Chinese farms in 2018 and 2019, they do cause chronic disease 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 fatal.

Although known infections are currently limited, if the strains spread widely, they could reduce pork production in the world’s largest consumer and producer; two years ago, swine fever wiped out half of China’s 400 million pigs. Pork prices are still at record highs and China is under pressure to bolster food security amid the COVID-19 pandemic.

“I don’t know where they came from, but we are finding mild infections in the field caused by some kind of gene-deleted virus,” 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 found strains of the virus missing both the MGF360 and CD2v genes, Yan said.

Research has shown that deleting certain African swine fever MGF360 genes creates immunity. But the modified virus was not developed into a vaccine because it tended to mutate into a harmful state later.

“You can sequence these things, these double deletions, and if it’s exactly the same as described in the lab, it’s too much of a coincidence, because you’re never going to get that exact deletion,” said Lucilla Steinaa, Senior Scientist at International Livestock Research Institute (ILRI) in Nairobi.

There is no approved vaccine against 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 that illicit vaccines have created accidental infections, which are now spreading.

The new strains could proliferate around the world through contaminated meat, infecting pigs fed with kitchen scraps. 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 he has issued at least three warnings against the use of unauthorized African swine fever vaccines, warning that they could have serious side effects and that producers and users could be charged with a criminal offense.

In August, the ministry announced it would test pigs for different strains of the virus as part of a nationwide investigation into illegal vaccine use.

Any strain with genetic deletions could indicate a vaccine was used, he said. No results have been published to date on the issue, which is very sensitive for Beijing. Notification of recent African swine fever outbreaks has been largely concealed. For a link to the report, click here

MAN-MADE STRAINS

After decades of research to produce a vaccine against the massive and complex swine fever virus, researchers around the world are focusing on live virus vaccines – the only type to show promise.

But these vaccines carry higher risks because even after the virus is weakened so as not to cause serious illness, it can sometimes regain its virulence.

One of these vaccines used in Spain in the 1960s caused 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 country has approved a vaccine against the disease.

A vaccine whose MGF360 and CD2v genes have been deleted is being tested by the Chinese Veterinary Research Institute in Harbin after showing promise.

Yan said he believed people had replicated the sequences of the studied viral strains, which have been published in the scientific literature, and that pigs injected with illicit vaccines based on them could infect others.

“It’s definitely man-made; it’s not a natural strain, ”he said.

Neither Johnson nor Yan have completely sequenced the new strains of swine fever. Beijing strictly controls who is allowed to work with the virus, which can only be handled in laboratories with high biosafety designations.

But several private companies have developed test kits to look for specific genes.

GM Biotech, based in China’s central Hunan province, said in an online article last week that it had developed a test that identifies whether the pathogen is a virulent strain, an attenuated strain with a single deleted gene or an attenuated double gene deleted strain.

The test helps pig producers because the new strains are “very difficult to detect at the initial stage of infection and have a longer incubation period after infection,” the company said.

The government has not said how widely illicit vaccines are used or who produced them. But “a large number” of pigs in China have nonetheless been vaccinated, Johnson said, a sentiment echoed by many other experts.

In 2004-2005, when strains of H5 avian influenza spread across Asia, Chinese labs produced several unlicensed live vaccines against avian influenza, said Mo Salman, professor of veterinary medicine at Colorado State University, who has worked on animal health in Asia. fears that they will produce dangerous new variants.

“The illegal ASF vaccine (s) currently in China is repeating history,” Salman said.