Results Show Promise for Experimental African Swine Fever Vaccine

ASF Possible Vaccine 020420
( OIE )

A new African swine fever (ASF) vaccine appears to be far more effective than previously developed vaccines, reports the American Society for Microbiology.

Although there is no commercially available vaccine against ASF, a deadly virus of pigs that is devastating the swine industry in Eastern Europe and Southeast Asia, government and academic investigators are furiously working to find answers.

In a recent study published in the Journal of Virology, both low and high doses of this ASF vaccine were 100% effective against the virus when the pigs were challenged 28 days post-inoculation, according to the Jan. 23 release from the American Society for Microbiology.

“The big deal with this vaccine is not only was it effective against the challenge at both a high dose and a low dose, but also in those challenged animals, there was no shedding of virus. This is so important so we’re not continually spreading virus with vaccinated animals,” explained Dave Pyburn, DVM, chief veterinarian for the National Pork Board.

The study was motivated by the 2007 ASF outbreak in the Republic of Georgia. This was the first outbreak in recent history outside of Africa and Sardinia, where ASF is endemic. Principal investigator Douglas P. Gladue, a senior scientist at Plum Island Animal Disease Center, said this particular strain has been highly lethal and highly contagious, spreading quickly to neighboring countries.

Researchers discovered that it’s also a new strain of the virus, now known as ASFV-G (G stands for Georgia) and is the genesis of the ASF spreading through Eastern Europe and east Asia.

There is limited cross-protection between strains of ASF, likely because the antigens and degree of virulence differ among them, and none of the historical experimental vaccines have been shown to be effective against ASFV-G, Gladue explained in the release.

Developing whole virus vaccines involves deleting virulence genes from the virus. But when the researchers deleted genes similar to those that had been deleted in older ASFV strains to attenuate them, "it became clear that ASFV-G was much more virulent" than the other historical isolates, because it retained a higher level of virulence, Gladue said in the release. 

The investigators recognized they needed a different genetic target in order to attenuate ASFV-G. They used a predictive methodology – a computational pipeline – to predict the roles of proteins on the virus. 

The computational pipeline predicted that a protein called I177l could interfere with the immune system of the pig. When they deleted this gene, ASFV-G was completely attenuated.

A major step forward
More work needs to be done to meet regulatory requirements for commercialization, but scientists are optimistic.

“This new experimental ASFV vaccine shows promise and offers complete protection against the current strain currently producing outbreaks throughout Eastern Europe and Asia,” Gladue said in the release.

Another exciting discovery from Pyburn’s perspective is that the researchers also necropsied those vaccinated animals and could not find the virus anywhere in the tissues. This is a huge step forward to slow the spread of disease. 

“What Plum Island Animal Disease Center needs now is a commercial partner to expand this research into larger groups of pigs so they can prove the vaccine works,” Pyburn said. “And we need to make sure this work happens as quickly as possible.”

Even if researchers start moving on the next step now, they are still multiple years away from getting an approved vaccine, Pyburn added.

“I am excited about this one,” he said. “It’s one of the best vaccine candidates we’ve seen as far as I’m concerned.”

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