According to Reuters, a new variant of African swine fever (ASF) has been identified in Chinese farms, and its origin could be illegal vaccines. These new strains have infected more than 1,000 pigs on various farms owned by New Hope Liuhe, China's fourth-largest producer, as well as at some other subsidiary facilities, as explained by Yan Zhichun, the company's chief scientific officer.
The new strains are not as deadly as those that have decimated China's pig population over the past two years, although they cause chronic diseases that reduce the number of healthy piglets. For now, the company has resorted to slaughtering infected pigs for propagation.
Strains with deleted genes
These new strains are characteristic because they lack some key genes present in the wild African swine fever virus. "I don't know where they come from, but we have found some mild field infections caused by some virus with deleted genes," said Yan Zhichun.
Last year, a veterinarian in Beijing diagnosed a less-lethal variant of ASF, caused by a virus that lacked certain genetic components, the MGF360 genes, and precisely in the virus strains that appeared in New Hope Liuhe, the viruses did not have the MGF360 genes. As well as the CD2v genes.
Research has shown that deleting some African swine fever MGF360 genes produces immunity, but a modified virus vaccine has not been developed because it tends to mutate later to a harmful state.
"These double deletions can be sequenced, and if they are 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, senior scientist at the International Livestock Research Institute (ILRI) in Nairobi.
Recourse to unapproved products
The lack of an approved ASF vaccine and many Chinese pig producers' desire to protect their pigs have led them to turn to unapproved products, say, experts, who fear that illegal vaccines have created accidental infections, which are now spreading.
China's Ministry of Agriculture and Rural Affairs has not made any official statements in this regard but has issued at least three warnings against the unauthorized use of ASF vaccines, warning that they could have serious side effects and that those who use them could be incurring.
In August, the ministry said it would test pigs for different strains of the virus as part of a national investigation into vaccines' illegal use. Any gene deletion strain could indicate a vaccine has been used, they warned, but no findings have been published so far on the subject, which is very sensitive for Beijing.
In search of the most effective solution
Researchers around the world are focusing on live virus vaccines as the most effective solution against ASF. At China's Harbin Veterinary Research Institute, a vaccine with the MGF360 and CD2v genes deleted is tested after some promising preliminary results.
The scientific director of New Hope Liuhe pointed out that the sequences of the virus strains have been replicated in the laboratory, that these works have been published in the scientific literature, and that pigs injected with illegal vaccines based on them could be infecting others. "It's definitely man-made, this is not a natural strain," he added.
The Chinese government strictly controls who can work with the virus, which can only be handled in highly biosafety laboratories. However, several private companies have developed test kits that can detect specific genes.
There are no official figures on the use of unapproved vaccines or data on who has produced them, but experts suspect that many pigs in China have been vaccinated.
When H5 bird flu strains spread through Asia in 2004 and 2005, Chinese laboratories produced several unauthorized live bird flu vaccines and recalled Mo Salman, a veterinary medicine professor at Colorado State University who has worked in health. animal in Asia and fears that new dangerous variants may be produced. "The current illegal ASF vaccines in China are repeating history," he warned.