Evaluation of one versus two doses of an inactivated Senecavirus A vaccine in weaned pigs

Authors: Buckley, Alexandra; HOFFMAN, KYLE - Oak Ridge Institute For Science And Education (ORISE); Lager, Kelly

Submitted to: International Pig Veterinary Society (IPVS)
Publication Type: Proceedings
Publication Acceptance Date: 6/5/2022
Publication Date: 6/23/2022
Citation: Devries, A.C., Hoffman, K., Lager, K.M. 2022. Evaluation of one versus two doses of an inactivated Senecavirus A vaccine in weaned pigs. Pig Veterinary Society International Congress Proceedings. IPVS 2022 Proceedings.

Interpretive Summary:

Technical Abstract: Introduction Senecavirus A (SVA), also known as Seneca Valley virus, is a causative agent of vesicular disease in swine and is grossly indistinguishable from vesicular disease caused by foot-and-mouth disease virus (FMDV). In countries that are FMDV-free, an investigation is required when a vesicular lesion is observed to rule out FMDV. These investigations can impart a substantial economic burden, especially if SVA remains endemic in swine populations. An efficacious vaccine could reduce the number of these investigations and the spread of SVA. The objective of this study was to compare the protective efficacy of one dose versus two doses of an inactivated SVA vaccine in weaned pigs. Materials and Methods Forty-eight 3-week-old pigs were purchased from a commercial swine herd and transported to the National Animal Disease Center in Ames, IA. Pigs were divided into four groups (n=12/group): one-dose + sham challenge (Group 1), one dose + challenge (Group 2), two-dose + challenge (Group 3), and sham + challenge (Group 4). One week after acclimation, pigs in Group 3 were vaccinated intramuscularly (IM) with 2 mL of whole-virus inactivated (binary ethylenimine) SVA (SVA/NADC4/2020) and an oil-in-water adjuvant at 12% v/v. Three weeks later, Groups 1-4 were vaccinated IM with 2 mL of either inactivated SVA or sham with adjuvant. Pigs were challenged intranasally with either SVA/NADC4/2020 (107 TCID50/mL) or sham two weeks later. Pigs were checked for vesicular lesions daily from 0-10 days post-challenge (dpc) and were scored using a 5-point scale. One point was assigned to each foot with an observed lesion and one point for a lesion on the snout. Pigs were rectal swabbed on 0-3, 5, 7, 10, 14 and 20 dpc. Blood was collected from animals on -36, -16, 0, 3, 5, 7, 14 and 20 dpc. Serum and swabs were tested for SVA nucleic acids by RT-qPCR. Sera was tested by virus neutralization assay using SVA/NADC4/2020 to measure the neutralizing antibody response after vaccination and challenge. Results Group 1 served as a vaccine control and these animals did not develop clinical signs or detectable SVA in serum or swabs tested. In Group 2, one animal developed a vesicular lesion at 4 dpc. This group had PCR positive rectal swabs on 1 dpc, but by 2 dpc only 2 animals were positive, and all subsequent samples were negative. None of the animals developed a detectable viremia. In Group 3, one animal developed a vesicular lesion at 9 dpc. In addition, Group 3 had positive rectal swabs on 1 and 2 dpc, but only a few animals were PCR positive on 3 dpc. Only one animal in Group 3 had a detectable viremia, which occurred on 3 dpc. As expected, Group 4 displayed the highest clinical scores and 11/12 animals presented with vesicular lesions during the observation period. This group also displayed the most consistent and extended detection of SVA nucleic acids in rectal swabs. Finally, SVA was detected in the serum of 7/12 animals on 3 and 5 dpc, but rapidly decreased with only two animals having a detectable viremia at 7 dpc. In those vaccinated animals, neutralizing titers were observed after one dose. As expected, neutralizing titers were higher in the two-dose group compared to the one-dose group at challenge. Mean titers began to decrease by the time of necropsy. Discussion and Conclusion Since the emergence of SVA in multiple countries in 2015, SVA has continued to remain endemic in some areas around the world. This work demonstrated that one dose of an SVA whole virus inactivated vaccine was as effective as a two-dose vaccine in reduction of the development of clinical signs and viral replication after homologous SVA challenge. An effective single-dose inactivated SVA vaccine would be economical and could be easier to apply in the field compared to a two-dose product. In addition, an efficacious SVA vaccine could provide a positive impact on the w