New China Swine Flu Fever Strains Point To Unlicensed Vaccines, Say Experts

In a fresh blow to the world¡¯s largest pork producer and still recovering from a devastating epidemic of the virus, a new form of African swine fever has been identified in China. Additionally, the country's pig farms are hit by the flu, that is most likely caused by illicit vaccines, say experts.

Two new strains of African swine fever have infected more than 1,000 adult female pigs (sows) on several farms owned by New Hope Liuhe, China's fourth-largest producer, as well as pigs being fattened for the firm by contract farmers, said Yan Zhichun, the company's chief science officer.

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New strains reduces number of healthy piglets born

In 2018 and 2019, the wild African swine fever virus ravaged China¡¯s farms, and the disease led to deaths of pigs in large numbers. But this time, the strains are missing one or two key genes and don't kill the pigs like the African swine flu. Instead, it causes a chronic condition that reduces the number of healthy piglets born, Yan told Reuters.

At New Hope, and many large producers, infected pigs are culled to prevent the spread, making the disease effectively fatal.

Reuters

Although the known infections are limited now, if the strains spread widely, they could slash pork output in the world's top consumer and producer; two years ago, swine fever wiped out half of China's 400 million-head pig herd. 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 sort of gene-deleted viruses," Yan said.

Virus survives for months in pork products

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 tended to later mutate back to 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 that exact deletion," said Lucilla Steinaa, principal scientist at the International Livestock Research Institute (ILRI) in Nairobi.

Jo-Anne McArthur

There is no approved vaccine for 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 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 issued warnings against use of illicit vaccines

China's Ministry of Agriculture and Rural Affairs has issued at least three warnings against use of unauthorised African swine fever vaccines, cautioning that they could have severe side effects and that producers and users could be charged with a criminal offence.

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 a vaccine had been used, it said. No findings have been published so far on the issue.

Reuters

After decades of research toward producing a vaccine against the huge, complex swine fever virus, researchers around the world are focussing on live-virus vaccines - the only type to have shown any promise.

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

"New strains are man-made, not natural"

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

"It's definitely man-made; this is not a natural strain," he said.

None of the experts have 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.

AFP

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 it had developed a test that identifies whether the pathogen is a virulent strain, a single-gene deleted attenuated strain, or a double-gene deleted attenuated 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 used illicit vaccines are or who has produced them. But a "vast amount" of pigs in China have nonetheless been vaccinated, Johnson said, a sentiment echoed by many other experts.