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New Chinese strains of swine fever point to unlicensed vaccines

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

FILE PHOTO: Pigs are seen on a backyard farm on the outskirts of Harbin, Heilongjiang Province, China, September 5, 2018. REUTERS / Hallie Gu

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 pigs being fattened for the company by contract farmers, said Yang Zhichun, chief scientist. director of the company.

Although strains that lack one or two key genes present in the African swine fever virus do not kill pigs like the disease that devastated Chinese farms in 2018 and 2019, they cause a chronic condition that reduces the number of healthy piglets born, Ian told Reuters. In New Hope and many large producers, infected pigs are slaughtered to prevent the spread, making the disease effectively fatal.

Although now known infections are limited, if the strains are widespread, they could reduce pork production in the world’s top consumers and producers; two years ago, the swine fever killed half of the herd of 400 million Chinese pigs. Pork prices are still at record levels and China is under pressure to boost 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 from the genes,” Ian said.

Wayne Johnson, a Beijing-based veterinarian, said he was diagnosed with a chronic or less deadly form of the disease in pigs last year. The virus did not have certain genetic components known as the MGF360 genes. New Hope found that both strains of the virus were missing from both the MGF360 genes and the CD2v genes, Yang said.

Studies show that deleting some MGF360 genes from African swine fever creates immunity. But the modified virus has not been developed into a vaccine, as it tends to mutate back to a harmful state later.

“You can sort 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 would never get exactly that deletion,” said Lucilla Steinaa, chief scientist at the International Livestock Research Institute (ILRI). ) in Nairobi.

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 resorted to unapproved products, industry insiders and experts say. They fear that illegal vaccines have created accidental infections that are now spreading.

The new strains can be spread worldwide through contaminated meat, infecting pigs that feed on kitchen waste. The virus is known to survive for months in some pork products.

The Chinese Ministry of Agriculture and Rural Affairs did not respond to two requests for comment.

But he issued at least three warnings against the use of unauthorized African swine fever vaccines, warning that they could have severe side effects and that producers and consumers 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 national investigation into the illegal use of vaccines.

Any strain with gene deletions could mean that a vaccine has been used, the report said. So far, no findings have been published on the issue, which is very sensitive for Beijing. Reports of recent outbreaks of African swine fever have been widely suppressed. Click here to link to the report


After decades of research into a vaccine against the huge complex swine fever virus, researchers around the world are focusing on live virus vaccines – the only one that has made promises.

But such vaccines carry a higher risk, because even after the virus is weakened so that it does not cause serious illness, it can sometimes regain its virulence.

Such a vaccine, used in Spain in the 1960s, caused chronic disease with swollen joints, skin lesions and respiratory problems in pigs, complicating efforts to eradicate African swine fever over the next three decades. Since then, no country has approved a vaccine against the disease.

A vaccine with deleted MGF360 and CD2v genes has been tested by the Chinese Institute of Veterinary Research in Harbin after it promised.

Ian said he believed that humans had reproduced the sequences of the strains of viruses studied, which were published in the scientific literature, and that pigs injected with illegal vaccines based on them could infect others.

“It was definitely man-made; this is not a natural strain, “he said.

Neither Johnson nor Ian sequenced the entirely new strains of swine fever. Beijing strictly controls who has the right to work with the virus, which can only be used in laboratories with high biosecurity labels.

But several private companies have developed test kits that can test for specific genes.

GM Biotech, based in the central Chinese province of Hunan, said in an online publication last week that it had developed a test to identify whether the pathogen was a virulent strain, a single-attenuated strain, a deleted or a double-gene attenuated strain.

The test helps pig producers because the 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 did not say how widely the illegal vaccines were used or who produced them. But “huge numbers” of pigs in China have nevertheless been vaccinated, Johnson said, a mood reflected by many other experts.

In 2004-5, when the H5 bird flu strains spread to Asia, Chinese laboratories produced several unauthorized live bird flu vaccines, said Mo Salman, a professor of veterinary medicine at Colorado State University who worked on animal health in Asia fears they may produce new dangerous options.

“The current illegal ASF vaccine in China repeats history,” Salman said.

Report by Dominic Patton. Edited by Gary Doyle

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