Deletion of the A137R Gene from the Pandemic Strain of African Swine Fever Virus Attenuates the Strain and Offers Protection against the Virulent Pandemic Virus

African swine fever virus (ASFV) is causing a devastating pandemic in domestic and wild swine within an extended geographical area from Central Europe to East Asia, resulting in economic losses for the regional swine industry. There are no commercial vaccines; therefore, disease control relies on identification and culling of infected animals. We report here that the deletion of the ASFV gene A137R from the highly virulent ASFV-Georgia2010 (ASFV-G) isolate induces a significant attenuation of virus virulence in swine. A recombinant virus lacking the A137R gene, ASFV-G-Delta A137R, was developed to assess the role of this gene in ASFV virulence in domestic swine. Animals inoculated intramuscularly with 10(2) 50% hemadsorption doses (HAD(50)) of ASFV-G-Delta A137R remained clinically healthy during the 28-day observational period. All animals inoculated with ASFV-G-Delta A137R had medium to high viremia titers and developed a strong virus-specific antibody response. Importantly, all ASFV-G-Delta A137R-inoculated animals were protected when challenged with the virulent parental strain ASFV-G. No evidence of replication of challenge virus was observed in the ASFV-G-Delta A137R-inoculated animals. Therefore, ASFV-G-Delta A137R is a novel potential live attenuated vaccine candidate and one of the few experimental vaccine strains reported to induce protection against the highly virulent ASFV Georgia virus that is the cause of the current Eurasian pandemic. IMPORTANCE No commercial vaccine is available to prevent African swine fever. The ASF pandemic caused by ASFV Georgia2007 strain (ASFV-G) is seriously affecting pork production in a contiguous area from Central Europe to East Asia. Here we report the rational development of a potential live attenuated vaccine strain by deleting a virus specific gene, A137R, from the genome of ASFV-G. The resulting virus presented a completely attenuated phenotype and, importantly, animals infected with this genetically modified virus were protected from developing ASF after challenge with the virulent parental virus. ASFV-G-Delta A137R confers protection even at low doses (10(2) HAD(50)), demonstrating its potential as a vaccine candidate. Therefore, ASFV-G-Delta A137R is a novel experimental ASF vaccine protecting pigs from the epidemiologically relevant ASFV Georgia isolate.

Automated summary

African swine fever virus (ASFV) is causing a devastating pandemic in swine industry from Central Europe to East Asia. A recombinant virus lacking the ASFV gene A137R, ASFV-G-Delta A137R, has been developed as a potential live attenuated vaccine candidate, showing significant virulence attenuation in swine and protective efficacy against the virulent parental virus. The ASFV-G-Delta A137R vaccine strain demonstrated the potential to protect pigs from the highly virulent ASFV Georgia isolate.