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New strains from swine fever in China point to unlicensed vaccines

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

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 Yan Zhichun, the company’s scientific director. .

Although the strains, which lack one or two key genes found 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 said. to Reuters. At New Hope and many large manufacturers, infected pigs are eradicated to prevent spread, making the disease effectively lethal.

Although the known infections are limited now, if the strains spread widely, they could reduce pork production at the world’s largest 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 do not know where they come from, but we do find some mild field infections caused by some kind of re-deleted viruses,” Yan said.

Wayne Johnson, a Beijing-based veterinarian, said he diagnosed a chronic or less deadly form of the disease in pigs last year. The virus lacked certain genetic components, known as the MGF360 genes. New Hope has found strains of the virus that are missing both the MGF360 genes and the CD2v genes, Yan said.

Research has shown that deletion of some MGF360 genes from African swine fever creates immunity. However, the modified virus was not developed into a vaccine because it tended to later mutate back into 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 much of a coincidence because you would never get the exact deletion,” said Lucilla Steinaa, lead researcher at 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 illegal vaccines have created unintended infections, which are now spreading.

The new strains could spread globally through contaminated meat and infect pigs fed kitchen waste. It is known that the virus survives for several 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 and warns that they can have serious side effects and that producers and users can be charged with a criminal offense.

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

Any strains with gene deletions could indicate that a vaccine had been used, it said. No findings on the subject have been published so far, which is very sensitive for Beijing. The reporting of the recent outbreaks of African swine fever was extensively covered. Click here for a link to the report


After decades of research into the production of a vaccine against the huge, complex swine fever virus, researchers around the world are focusing on live virus vaccines – the only type that has shown any promise.

However, such vaccines have higher risks 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 a chronic disease with swollen joints, skin lesions and respiratory problems in pigs that complicated the 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 MGF360 and CD2v genes deleted is undergoing trials by China’s Harbin Veterinary Research Institute after showing promise.

Yan said he believes people have replicated the sequences of virus strains being studied, which have been published in scientific literature, and that pigs injected with illegal vaccines based on them could infect others.

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

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

However, several private companies have developed test kits that can control 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 attenuated strain, or a double gene-deleted weakened strain.

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 widespread illegal vaccines are or who produced them. But a “large number” of pigs in China have nevertheless been vaccinated, Johnson said, a sentiment repeated by many other experts.

In 2004-5, when the H5 avian flu strains spread across Asia, Chinese laboratories produced several unauthorized live avian flu vaccines, said Mo Salman, a professor of veterinary medicine at Colorado State University who has worked with animal health in Asia and raised fears that they can produce new dangerous varieties.

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

Reporting by Dominique Patton. Editing by Gerry Doyle

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