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African swine fever strains point to unlicensed vaccines in China
A BLOW to the world’s largest pork producer still recovering from a devastating epidemic of African swine fever, the new form of African swine fever identified in Chinese pig farms has possibly been caused by illicit vaccines.
New Hope Liuhe chief science officer Yan Zhi-
The strains are missing one or two key genes present in the wild Af-
With infected pigs being culled to prevent the spread, the disease is ef- fectively fatal.
Only two years ago, AFS decimated half of China’s 400 million-head pig herd.
Beijing-based veteri- narian Wayne Johnson said he diagnosed a chronic less-lethal form of the disease in pigs last year.
The fear is that illicit vaccines have created ac- cidental infections, which are now spreading.
After decades of re- search towards producing a vaccine against the com- plex swine fever virus, re- searchers globally are fo- cussing on live-virus vac- cines – the only type to have shown any promise.
chun said two new strains of African swine fever had infected more than 1000 sows on several farms owned by China’s fourth-largest producer, as well as pigs being fattened for the firm by contract farmers.
rican swine fever virus and don’t kill pigs as did the disease that ravaged China’s farms in 2018 and 2019, they do cause a chronic condition that reduces the number of healthy piglets born.
While known infections are currently limited, if the strains spread, they could wipe out China’s pork output – the world’s top consumer and pro- ducer.
record levels and China is under pressure to strengthen food security amid the COVID-19 pan- demic.
would never get that exact deletion.”
have been published to date, which is highly sen- sitive for Beijing.
Pigs are seen at a backyard farm on the outskirts of Harbin, Heilongjiang province, China September 5, 2018. Photo: REUTERS/Hallie Gu
No findings on the issue
Yan said he believed that people have replicated the sequences of virus strains being studied, which have been published in scien- tific literature, and that pigs injected with illicit vaccines based on them could be infecting others.
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“I don’t know where they come from, but we find mild field infections caused by gene-deleted viruses,” Yan said.
There is no approved vaccine for ASF, which is not harmful to hu- mans, though many Chi- nese farmers struggling to protect their pigs have resorted to unapproved products.
Reporting of the recent ASF outbreaks was exten- sively covered up.
The virus lacked cer- tain genetic components, known as the MGF360 genes.
The new strains could thrive globally through contaminated meat, in- fecting pigs fed on kitchen waste.
However, such vaccines carry higher risks be- cause even after the virus is weakened so it doesn’t cause serious illness, it can occasionally recover its virulence.
New Hope has found strains of the virus missing both the MGF360 genes and the CD2v genes.
The virus is known to survive for months in sev- eral pork products.
One such vaccine used in Spain in the 1960s caused a chronic disease with swollen joints, skin lesions and respiratory is- sues in pigs that compli- cated efforts to eradicate ASF over the next three decades.
Research has shown that deleting several MGF360 genes from ASF creates immunity.
China’s Ministry of Ag- riculture and Rural Af- fairs has issued at least three warnings against use of unauthorised ASF vaccines, cautioning that they could have severe side-effects and that pro- ducers and users could be charged with a criminal offence.
But the modified virus was not developed into a vaccine because it tended to mutate back to a harmful state later.
In August, the ministry said it would test pigs for different strains of the virus as part of a nation- wide investigation into il- legal vaccine use.
Since then, no nation has approved a vaccine for the disease.
Nairobi-based Interna- tional Livestock Research Institute principal scien- tist Lucilla Steinaa said: “You can sequence these things, these double dele- tions, and if it’s exactly the same as described in the lab, it’s too much of a coincidence, because you
Any strains with gene deletions could indicate a vaccine had been used.
A vaccine with both MGF360 and CD2v genes deleted has been under- going trials by China’s Harbin Veterinary Re- search Institute after showing promise.
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“It’s definitely man- made; this is not a natural strain,” Yan 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 handled in labora- tories with high biosecu- rity designations.
Though several private companies have devel- oped test kits that can check for specific genes.
GM Biotech based in China’s central Hunan province said it had devel- oped 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 pro- ducers because the new strains are very difficult to detect at the initial stage of infection and have a longer incubation period after infection.
The government has not confirmed how widely used illicit vaccines are or who has produced them.
However, a great number of pigs in China have been vaccinated, Johnson said – a sentiment echoed by many other experts.
Colorado State Univer- sity professor of veteri- nary medicine Mo Salman said in 2004-5, when the H5 bird flu strains were spreading across Asia, Chinese laboratories pro- duced several unauthor- ised live bird flu vaccines, raising fears that they could produce dangerous new variants.
Prof Salman who has worked on animal health in Asia said: “The current ASF unlawful vaccine use in China is repeating his- tory.”

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