BEIJING (Reuters) – A new form of African swine fever identified on pig farms in China is likely caused by illicit vaccines, industry sources said, a new blow to the world’s largest pig producer, still recovering from a devastating epidemic of the virus.
Two new strains of African swine fever have infected more than 1,000 sows on various 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 science director .
Although strains, which lack one or two major genes present in the African swine fever virus, do not kill pigs as the disease that devastated China’s farms in 2018 and 2019, they cause a chronic disease that reduces the number of healthy piglets born, Yan told Reuters. At New Hope, and at many large producers, infected pigs are euthanized to prevent spread, making the disease effectively fatal.
Although known infections are now limited, if the strains spread widely, they can reduce pork production in the world’s largest consumer and producer; two years ago, swine fever wiped out half of China’s 400 million 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 found some mild field infections caused by some type of virus excluding genes,” said Yan.
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 MGF360 genes. New Hope found strains of the virus without the MGF360 and CD2v genes, Yan said.
Research has shown that the exclusion of some MGF360 genes from African swine fever creates immunity. But the modified virus was not developed into a vaccine because it tended to mutate back to a harmful state.
“You can sequence these things, these double exclusions, and if it’s exactly the same as described in the lab, it’s quite a coincidence, because you would never get that exact exclusion,” said Lucilla Steinaa, chief scientist at the International Livestock Research Institute (ILRI) in Nairobi.
There is no approved vaccine for African swine fever, which is not harmful to humans. However, many Chinese farmers struggling to protect their pigs have turned to unapproved products, industry experts said. They fear that illicit vaccines have created accidental infections, which are now spreading.
The new varieties can proliferate globally through contaminated meat, infecting pigs that are fed with kitchen scraps. The virus survives for months in some pig products.
China’s Ministry of Agriculture and Rural Affairs did not respond to two requests for comment.
But it 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 accused of a crime.
In August, the ministry said it would test pigs for different strains of the virus as part of a national investigation into the illegal use of vaccines.
Any strain with gene deletion could indicate that a vaccine was used, he said. No findings have yet been published on the subject, which is highly sensitive for Beijing. Reports of recent outbreaks of African swine fever have been largely covered up. For a link to the report, click here
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After decades of research to produce a vaccine against the huge and complex swine fever virus, researchers around the world are focusing on live virus vaccines – the only type that has shown promise.
But these vaccines are at greater risk because, even after the virus is weakened so as not to cause serious illness, it can sometimes recover its virulence.
One of those vaccines used in Spain in the 1960s caused a chronic illness with swollen joints, skin lesions and respiratory problems in pigs that complicated efforts to eradicate African swine fever in the next three decades. Since then, no nation has approved a vaccine for the disease.
A vaccine with the deleted MGF360 and CD2v genes is being tested by the Harbin Veterinary Research Institute of China after it shows promise.
Yan said he believed that people replicated the strains of virus strains under study, which were published in the scientific literature, and that pigs injected with illicit vaccines based on them may be infecting others.
“It is definitely man-made; this is not a natural variety, ”he said.
Neither Johnson nor Yan have 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 biosafety designations.
But several private companies have developed test kits that can check specific genes.
GM Biotech, based in Hunan Province, China, said in an online post last week that it has developed a test that identifies whether the pathogen is a virulent strain, an attenuated strain with a single gene or an attenuated strain with a gene double.
The test helps pig producers because the new strains are “very difficult to detect at an early stage of infection and have a longer incubation period after infection,” said the company.
The government did not say to what extent illicit vaccines are widely used or who produced them. Still, a “large number” of pigs in China have been vaccinated, said Johnson, a sentiment shared by many other experts.
In 2004-5, when strains of H5 avian flu were spreading across Asia, Chinese laboratories produced several unauthorized live vaccines against bird flu, said Mo Salman, professor of veterinary medicine at Colorado State University, who worked in animal health in Asia, raising fears that they may produce new dangerous variants.
“The current illegal ASF vaccines in China are repeating themselves in history,” said Salman.
Reporting by Dominique Patton. Gerry Doyle Edition