17 February 2021- Late last month, reporting from China revealed the existence of at least two new strains of African Swine Fever (ASF) virus, which were remarkable for the absence of particular genes. These strains do not cause the characteristic high mortality rates of ASF (where the wild type virus kills nearly 100% of the pigs it infects.) Instead, they are said to cause a chronic form of ASF which impacts the reproductive success of pigs.
Unfortunately, the existence of a less deadly ASFv is not the good news it might appear to be on the surface. That is because it is suspected that these new strains did not evolve naturally, but rather were the consequence of “illicit” vaccines. According to experts quoted by Reuters, it is extremely unlikely that the virus would have naturally mutated into this exact form, where two specific genes previously identified by laboratory research as important for a potential vaccine strain were deleted.
In a conversation with Feedinfo News Service, Dr. Jishu Shi, Professor in the Laboratory of Vaccine Immunology at Kansas State University and Director of the U.S.-China Center for Animal Health, largely concurs. “If the strain coming from China didn’t have [these specific mutations] before—let’s say, a different genotype of ASF virus shows up—presumably it was introduced intentionally as a potential vaccine,” he explains. “The idea that certain genes can be key to the attenuation of the virus, that’s available in the literature already. So if you start to see strains with those genes deleted, showing up not in the wild but in farms in China, that’s assumed to have come from an experimental vaccine.”
Of course, while considered unlikely, the possibility that these strains evolved naturally cannot be ruled out entirely—at least not without more data than Dr. Shi has himself. Indeed, recent research by the Military Veterinary Institute in Changchun, also reported on by Reuters, contends that the virus is also undergoing natural mutation towards less virulent forms in China (as well as elsewhere such as the Baltic states), although this research is said to concern different genetic mutation than those purportedly associated with the illicit vaccines.
Still, Dr. Shi confirms that the process of creating a mutated form of the virus with such a genetic modification does not necessarily require highly specialized knowledge or skill that is only available to a select few who have long been working with this particular virus. “I think, technically, it is not that difficult… a lot of qualified molecular biologists could do it.” And as previously mentioned, the genes in question had already been identified within the ASFv research circles as having potential applications for an ASF vaccine, although, as Reuters points out, previous attempts at a vaccine based on them had been found to have safety issues. Still, Dr. Shi makes the distinction that, while physically making such a virus would be within the skill set for many scientists, whether they would have been allowed to do it was a different question, as few laboratories worldwide are authorized to work with such a dangerous virus.
It is striking, for someone who is not an expert in molecular biology, to learn that a technology with such high stakes could basically be developed clandestinely –not exactly in the garage, but almost in the laboratory equivalent of one. Dr. Shi is, however, careful to point out that to call such illicit products “vaccines” is, frankly, to give them too much credit. “A vaccine, in my mind, is something that has been approved by the regulatory agencies. The fact that you’ve created a mutant doesn’t mean it’s a vaccine.” In part, this stems from a concern that such reckless actors not give an undeserved bad name to what is a safe and legitimate vaccine technology—because as it happens, the process of removing certain carefully selected genes in order to create a modified live attenuated vaccine is, in fact, a widely used technique used to make perfectly good, sanctioned vaccines as well. “There are attenuated vaccines that work, commercially available, like for PRRS and other [diseases]. They’re not perfect, but they do the job…in fact, for classical swine fever, the C-strain, or other modified live vaccines, are very safe and efficacious.”
Meanwhile, the damage from this mutant strain should not be underestimated. Most mutants, including these, are somewhat attenuated, so not as devastating to an individual animal as the wild type virus. However, he explains, this comes with an extremely problematic trade-off in terms of its ability to spread. Currently the only effective control once ASF is on the premises is very quick intervention, with targeted culling or removal of infected animals and those in contact with them. “But with the attenuated [virus], you don’t see the clinical signs, so unless you are doing testing, you don’t know the herd has the virus, until the pigs are under stress… then this attenuated virus becomes a problem, but by then it’s too late, it’s already been transmitted to many pigs. So in that sense, it’s really increasing the difficulty [of controlling ASF] under the current conditions, when we don’t have a safe and efficacious vaccine.”
Dr. Shi is definitely sympathetic to the enormous strain being put on producers in regions challenged by ASF. “In a desperate situation, a lot of people would rather have something [to help them minimize the threat of ASF for their farms],” he acknowledges. Those who might have turned to illicit vaccines “didn’t know it was poison, that it would cause more damage than the relief they hoped for.” He says that for his part, he hopes producers will draw a lesson from the experience about the dangers of employing unapproved animal health solutions, and that it encourages those researchers who are developing a vaccine and seeing the correct approvals to take their time to do all the necessary safety and testing, without rushing. “That may be the best chance for now.”
This is part I of a multi-part series on the quest for an ASF vaccine. Check back in coming weeks for future installments on why the development of an ASF vaccine has proven so difficult, and on different approaches being tried by teams worldwide.