African swine fever (ASF) is currently causing a major pandemic affecting the swine industry and
protein availability from Central Europe to East and South Asia. No commercial
vaccines are available, making disease control dependent on the elimination of affected animals. Here, we show that the deletion of the African swine fever virus (ASFV) E184L gene from the highly virulent ASFV Georgia 2010 (ASFV-G) isolate produces a reduction in virus virulence during the
infection in swine. Of domestic pigs intramuscularly inoculated with a recombinant virus lacking the E184L gene (ASFV-G-ΔE184L), 40% experienced a significantly (5 days) delayed presentation of clinical disease and, overall, had a 60% rate of survival compared to animals inoculated with the virulent parental ASFV-G. Importantly, all animals surviving ASFV-G-ΔE184L
infection developed a strong antibody response and were protected when challenged with ASFV-G. As expected, a pool of sera from ASFV-G-ΔE184L-inoculated animals lacked any detectable antibody response to
peptides partially representing the E184L
protein, while sera from animals inoculated with an efficacious
vaccine candidate, ASFV-G-ΔMGF, strongly recognize the same set of
peptides. These results support the potential use of the E184L deletion for the development of
vaccines able to differentiate infected from vaccinated animals (DIVA). Therefore, it is shown here that the E184L gene is a novel ASFV determinant of virulence that can potentially be used to increase safety in preexisting
vaccine candidates, as well as to provide them with DIVA capabilities. To our knowledge, E184L is the first ASFV gene product experimentally shown to be a functional DIVA antigenic marker. IMPORTANCE No commercial
vaccines are available to prevent
African swine fever (ASF). The ASF pandemic caused by the ASF virus Georgia 2010 (ASFV-G) strain is seriously affecting pork production in a contiguous geographical area from Central Europe to East Asia. The only effective experimental
vaccines are viruses attenuated by deleting ASFV genes associated with virus virulence. Therefore, identification of such genes is of critical importance for
vaccine development. Here, we report the discovery of a novel determinant of ASFV virulence, the E184L gene. Deletion of the E184L gene from the ASFV-G genome (ASFV-G-ΔE184L) produced a reduction in virus virulence, and importantly, animals surviving
infection with ASFV-G-ΔE184L were protected from developing ASF after challenge with the virulent parental virus ASFV-G. Importantly, the virus
protein encoded by E184L is highly immunogenic, making a virus lacking this gene a
vaccine candidate that allows the differentiation of infected from vaccinated animals (DIVA). Here, we show that unlike what is observed in animals inoculated with the
vaccine candidate ASFV-G-ΔMGF, ASFV-G-ΔE184L-inoculated animals do not mount a E184L-specific antibody response, indicating the feasibility of using the E184L deletion as the antigenic marker for the development of a DIVA
vaccine in ASFV.