SCIENTISTS HAVE made progress in the effort to develop a vaccine for African Swine Fever.

The virus continues to devastate domestic and wild swine herds across Europe, Asia and Africa, with increasing reports of it moving further west.

The race to develop a commercially viable vaccine has been slow but recent work by the Pirbright Institute and UCL has helped to create the first complete genetic road map, which reveals the order that different sets of ASFV genes are turned on throughout its infection cycle.

“ASFV has a very large DNA genome,” said Dr Linda Dixon, head of the ASFV Group at Pirbright. “For comparison, the influenza virus expresses eight genes, whereas ASFV expresses between 150 and 190, which has so far made it difficult for scientists to identify and determine the significance of each gene. Our study helps to untangle which genes are important during different stages of infection to better understand their functions.”

Genes, including those in ASFV, are activated through a process called transcription. This is carried out by a molecular machine called RNA polymerase, which serves as ‘gatekeeper’ by ensuring that the information coded in the DNA is expressed at the correct time during infection. The RNA polymerase finds genes based on specific DNA sequences, or ‘promoters’, that are located before a gene.

The team demonstrated that genes expressed during early infection have different promoters to those expressed later, allowing the virus to shift the pattern of activated genes according to the stage of infection. Genes used for DNA replication and immune system evasion are switched on early in the infection cycle, whereas those involved in creating proteins for the new virus particles are activated later.

Professor of Molecular Biophysics at UCL, Finn Werner, added: “Our data shows ASFV has a complex and mammalian-like method for controlling gene expression, that uses specific promoters to enable RNA polymerase to differentiate between which genes it should express when during viral infection. Our study has also uncovered over 30 novel genes that were previously unknown.”

ASFV causes an often-lethal haemorrhagic fever in domestic pigs and wild boar and in 2019 resulted in the death of nearly seven million pigs.

Due to effective vaccines or antiviral drugs still not being available, biosecurity measures are essential for outbreak prevention.

One of the newest routes which are being investigated for transferring the virus is contaminated feed and feed components.

The latest research has shown that the virus can survive for extended periods of time in feed and that this is then fed to domestic pigs, thereby introducing the virus to that herd.

Animal feed components can spread the ASF virus across borders with research trials illustrating its stability and capacity to survive long-haul travel, including transboundary shipping.

Contaminated meat is still the most common and high risk means of the virus moving, because illegal movement of meat across borders is so common and the virus survives well in pork.

However, there is a significant volume of feed ingredients being imported to the US from ASF positive regions. Soy-based products are being imported daily and research has shown that soy provides a protective environment for the virus which can pose a big risk.