Scientists from The Pirbright Institute in the U.K. have taken a step closer to developing a vaccine for African swine fever (ASF). In a recent trial, results of which were published in Vaccines, 100% of pigs immunized with the new vaccine survived a lethal dose of ASF virus, Pirbright said in a May 21 announcement.

ASF causes fever, loss of appetite, vomiting and bloody diarrhea in pigs and wild boars, with case fatality rates reaching 100%. The disease continues to spread across Eastern Europe and Asia, resulting in the death of more than 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 has developed a vectored vaccine that 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 that prime the pig's 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 ASF virus, although some clinical signs of disease did develop, the institute said.

Dr. Chris Netherton, head of Pirbright’s ASF Vaccinology Group, said, “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.”

Pirbright said this type of vaccine also will enable the differentiation of infected animals from those that have received a vaccine (known as DIVA), which is an important feature because it allows vaccination programs to be established without sacrificing the ability to conduct transboundary 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,” Netherton noted.

“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," U.K. chief veterinary officer Christine Middlemiss said.

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