Go Pig or Go Home: Promising Vaccine Developed Against African Swine Fever

African swine fever (ASF) is a deadly viral disease infecting wild and domestic pigs with an extremely high mortality rate of 95-100%. In this blog, we discuss the history of African swine fever and a recently developed vaccine candidate for the potential treatment of the disease.

Making a Pig’s Ear of Things

The highly contagious African swine fever virus (ASFV) was first detected in the 1920s in East Africa and later reached Europe in the 1950s where it rapidly spread through the porcine population (Li et al 2022). This stubborn virus persisted in Europe for decades, briefly disappearing in 1995 before reappearing in 2007 in Georgia. In 2020, fears grew as ASF crept closer and closer toward the two greatest pig-producing countries in the EU — France and Germany (Weir 2022).

Asia was relatively unscathed by ASF until the recent outbreak in 2018 emerged to wreak havoc, spreading at an alarming rate through China, the world’s largest producer of pork. Due to its highly contagious nature and lack of treatment options, disease control is mediated by the culling of infected and exposed animals. It has been estimated that ASF caused the death, either directly or indirectly, of around 225 million pigs in China alone (Khanna 2022). This has led to a drastic strain on the piggy bank, with the economic loss due to this outbreak estimated to be approximately 111.2 billion US dollars in 2019 (You et al. 2021).

After learning of the vicious and persistent character of this virus, it’s easy to think of eradication as something that will happen when pigs fly. However, a lab in France has recently developed a potential vaccine for the disease with initial results looking promising (Bourry et al. 2022). 

Promising Results

Researchers at ANSES’s Ploufragan-Plouzané-Niort Laboratory were attempting to inactivate the Georgia 2007/1 strain of the virus with heat treatment and, by chance, created an attenuated viral strain, which they have termed ASFV-989. While investigating this new attenuated strain further, it became apparent that it could be useful as a vaccine.

The researchers carried out three trials on a total of 65 pigs to investigate the effects of ASFV-989 in vivo. In trials 1 and 2, porcine subjects were inoculated with either the attenuated strain, or the original Georgia strain of the virus, by one of two routes; intramuscularly (IM) or oronasally (ON). Unsurprisingly, all pigs infected with the Georgia strain developed the typical symptoms associated with the disease and had to be euthanized six days after the initial infection. However, the pigs infected with the ASFV-989 strain faired remarkably better, with only 2 out of 11 IM inoculated animals developing severe symptoms and none of the ON inoculated animals severely affected. PCR analysis of the animals’ blood one week after infection showed that the ASFV-989 strain had a 100-fold lower viral load than the original strain. Interestingly, the blood of the ON ASFV-989 inoculated pigs also had a notably lower viral load than those inoculated via the IM route, suggesting that ON administration of the vaccine may be a more effective method of delivery.

Upon infection with the original ASFV strain, the fatal decline in health occurs too rapidly for the body to develop specific antibodies to protect against the virus. However, pigs infected with the ASFV-989 strain were able to mount an antibody response. Therefore, to investigate any possible therapeutic effects of inoculation with ASFV-989, pigs were reinfected with the original Georgia strain 28 days after initial inoculation and monitored for the development of symptoms. None of the pigs that were pre-inoculated with ASFV-989 prior to infection with the Georgia strain developed any disease-related symptoms and all animals in this group survived the infection, indicating its potential as an effective vaccine to protect against ASF (Bourry et al. 2022).

Going the Whole Hog

While initial results look promising, additional studies, such as assessing whether ASFV-989 can regain its virulent properties or be transmitted amongst animals, are still required before this strain can be approved as a vaccine. According to a recent press release, the scientists at ANSES carried out further research to optimize this approach for vaccine development by successfully amplifying the attenuated strain in cell lines in vitro, bypassing the need for primary porcine cells and enabling production on a large scale. Surprisingly, ASFV-989 produced by this method led to even fewer symptoms than was observed previously, whilst still maintaining its efficacy. If the results remain positive after additional testing, wild boar are suggested to be the initial receivers of the vaccine, since they are most affected by the disease and represent a great risk to the domestic population.

Overall, the development of a vaccine against this pig-headed virus seems increasingly likely and would make many people globally happy as a pig in mud!