Scientists at The Pirbright Institute have found that deleting a gene of the African swine fever virus (ASFV), a severe and often fatal disease of pigs, reduces its ability to cause infection and protects against a strain of the virus that causes severe disease.
In the study, published in the Journal of Virology, Pirbright scientists deleted an ASFV gene that codes for a protein thought to play a role in suppressing the pig immune system. The resulting modified virus was still able to replicate, but showed a dramatically reduced ability to cause infection, meaning the pigs all survived and only displayed mild clinical signs. After being exposed to the modified strain, the pigs were protected against further infection from a natural strain of ASFV.
Dr Linda Dixon, leader of the ASF group at Pirbright, said: “Now that we have shown the modified virus has the ability to protect pigs against a natural strain, the next steps will be to make more gene deletions that will reduce the clinical signs exhibited by pigs after vaccination.
“We will also be investigating the precise role the protein plays during infection. This information will help us understand how it interacts with the host immune system and if the protein directly prevents immune processes or if it has other roles we haven’t yet identified. Knowing more about the gene and protein will make it easier for us to modify the virus further and create a vaccine that is effective and safe.”
ASF has no vaccine, so the continued efforts of scientists to identify vaccine candidates is essential. The disease is currently spreading further across Europe, with the latest outbreaks described in Romania for the first time. ASF can be very difficult to identify, as it displays similar clinical signs to other pig diseases, with the most harmful strains killing pigs before specific signs become apparent. In regions where infected wild boar are present transmission of ASFV to domestic pigs also complicates the control of the disease.
Current prevention strategies focus around import controls and the education of farm owners on ASF and biosecurity to prevent infection and diagnose rapidly. However, these tools are currently not robust enough to stop the disease spreading across Eastern Europe and Russia, making the need for a vaccine even more pressing.
This Pirbright research has shown that the modified virus could be used as a component of a live attenuated vaccine; a type of vaccine that contains a weakened version of the virus which is able to mimic infection and cause an immune response without causing harm to the animal. These vaccines have recently been reviewed in an article published in Vaccines by the European Union ASF Expert Working Group, which includes Dr. Linda Dixon.
The experts established that live attenuated vaccines are the most promising and best positioned candidates for use in the future against ASF. Although there are still important issues such as safety and effectiveness that need resolving before these vaccines are available commercially, Pirbright scientists anticipate further research on this candidate could lead to the development of an ASF vaccine.
This research was funded by the Biotechnology and Biological Sciences Research Council (BBSRC), grant number (BB/L004267/1) and the European Union’s Seventh Framework Programme (FP7/2007-2013) under Grant Agreement nº 311931, ASFORCE.