Deletion of the EP402R gene from the genome of African swine fever vaccine strain ASFV-G-deltaI177L provides the potential capability of differentiating between infected and vaccinated animals

Authors: Borca, Manuel; Ramirez-Medina, Elizabeth; Espinoza, Nallely; RAI, AYUSHI - Oak Ridge Institute For Science And Education (ORISE); Spinard Iii, Edward; Velazquez, Lauro; VALLADARES, ALYSSA - Kansas State University; Silva, Ediane; Burton, Leeanna; MEYERS, AMANDA - Oak Ridge Institute For Science And Education (ORISE); Clark, Jason; WU, PING - Animal And Plant Health Inspection Service (APHIS); Gay, Cyril; Gladue, Douglas

Submitted to: Viruses
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2024
Publication Date: 2/28/2024
Citation: Borca, M.V., Ramirez Medina, E., Espinoza, N.N., Rai, A., Spinard III, E.J., Velazquez Salinas, L., Valladares, A., Silva, E.B., Burton, L.J., Meyers, A., Clark, J.A., Wu, P., Gay, C.G., Gladue, D.P. 2024. Deletion of the EP402R gene from the genome of African swine fever vaccine strain ASFV-G-deltaI177L provides the potential capability of differentiating between infected and vaccinated animals. Viruses. 16(3). Article 376. https://doi.org/10.3390/v16030376.
DOI: https://doi.org/10.3390/v16030376

Interpretive Summary: This report describes an additional deletion in the USDA African swine fever vaccine that provides potential DIVA capability or the ability to differentiate between vaccinated and non-vaccinated animals using the serological marker that was deleted.

Technical Abstract: The ASFV strain ASFV-G-deltaI177L is a safe and efficacious vaccine which induces protection against challenge with its parental virus, the Georgia 2010 isolate. Although a genetic DIVA assay has been developed for this vaccine, there still is not a serological DIVA test to differentiate animals vaccinated with ASFV-G-deltaI177L from those infected with wild type viruses. In this report, we describe the development of an ASFV-G-deltaI177L strain having deleted the EP402R gene, which encodes for the viral protein responsible of mediating the hemoadsorption with swine erythrocytes. The resulting virus, ASFV-G-deltaI177L/deltaEP402R, does not have a decreased ability to replicate in swine macrophages when compared with the parental ASFV-G-deltaI177L. Domestic pigs intra-muscularly (IM) inoculated with either 102 or 106 HAD50 of ASFV-G-deltaI177L/deltaEP402R remain clinically normal, when compared with a group of mock vaccinated animals, indicating the absence of residual virulence. Interestingly, infectious virus could not be detected in blood of any of the ASFV-G-deltaI177L/deltaEP402R inoculated animals in either group at any of time point tested. Furthermore, while all mock inoculated animals presented a quick and lethal clinical form of ASF disease after the IM challenge with 102 HAD50 of highly virulent parental field isolate Georgia 2010 (ASFV-G), all ASFV-G-deltaI177L/deltaEP402R inoculated animals were protected, remaining clinically normal until the end of the observational period. Most of the ASFV-G-delta177L/deltaEP402R inoculated pigs developed strong virus specific antibody responses against viral antigens, reaching maximum levels at day 28 post inoculation. Importantly, all sera collected at that time point in the ASFV-G-deltaI177L/deltaEP402R inoculated pigs did not react in a direct ELISA using plates coated with recombinant EP402R protein product as antigen. Conversely, the EP402R protein product was readily recognized by the pool of sera from animals immunized with recombinant live attenuated vaccine candidates ASFV-G-deltaI177L, ASFV-G-deltaMGF and ASFV-G-delta9GL/deltaUK. Therefore, ASFV-G-deltaI177L/deltaEP402R is a novel safe and efficacious candidate with potential to be used as an antigenically marker vaccine.