Scientists from The Pirbright Institute say they are a step closer in the race to develop a vital vaccine for African swine fever. In their recent trial, published in Vaccines, 100% of pigs immunized with the new vaccine survived a lethal dose of ASF virus.

ASF causes fever, loss of appetite, vomiting and bloody diarrhea in pigs and wild boar, with case fatality rates reaching 100%. The disease continues to spread across Eastern Europe and Asia, resulting in the death of over 7 million pigs worldwide in 2019 and disrupting trade systems that are intertwined with the pork industry. With no commercial vaccine available, stringent biosecurity measures and the culling of susceptible animals are the only methods available to bring ASF under control.

The Pirbright team have developed a vectored vaccine, which uses a non-harmful virus (the vector) to deliver eight strategically selected genes from the ASF virus genome into pig cells. Once inside the cell, the genes produce viral proteins which primes the pig immune cells to respond to an ASF infection. All pigs that were immunized with the vaccine were protected from severe disease after challenge with an otherwise fatal strain of ASFV, although some clinical signs of disease did develop.   

Chris Netherton, head of Pirbright's ASF Vaccinology Group, says "It is very encouraging to see that the genes we have selected are able to protect pigs against ASF. Although the pigs showed clinical signs of infection after challenge with the virus, our study has shown for the first time that a vectored vaccine against ASF is a realistic possibility."

This type of vaccine will also enable the differentiation of infected animals from those that have received a vaccine (DIVA). This is an important feature, as it allows vaccination programs to be established without sacrificing the ability to trade.

"Our next step will be to uncover the mechanisms behind how the proteins produced by the virus genes stimulate the immune system so we can refine and add to those included in the vaccine to improve effectiveness," says Netherton.

Christine Middlemiss, the UK's chief veterinary officer, says: "This is a very encouraging breakthrough and it means we are one step closer to safeguarding the health of our pigs and the wider industry's role in global food supply from African swine fever. While there has never been an outbreak of African swine fever in the UK, we are not complacent and already have robust measures in place to protect against animal disease outbreaks."

This research was funded by the Department for Environment, Food and Rural Affairs and the Biotechnology and Biological Sciences Research Council, part of UK Research and Innovation.

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