Passive immunity to porcine epidemic diarrhea virusfollowing immunization of pregnant gilts with a recombinant orf virusvector expressing the spike protein

AbstractPassive immunity is critical for protection of neonatal piglets against porcine epidemic diarrhea virus (PEDV). Here, weinvestigated the immunogenicity of an orf virus (ORFV) vector expressing the full-length spike (S) protein of PEDV (ORFVPEDV-S) in pregnant gilts and its ability to confer passive immunity and protection in piglets. Three doses of ORFV-PEDV-Swere given to two groups of PEDV-negative pregnant gilts, with the last dose being administered two weeks prior to farrowing.One of the two groups immunized with the ORFV-PEDV-S recombinant virus was also exposed to live PEDV orallyon day 31 post-immunization (pi). Antibody responses were assessed in serum, colostrum and milk of immunized gilts, andpassive transfer of antibodies was evaluated in piglet sera. The protective efficacy of ORFV-PEDV-S was evaluated afterchallenge of the piglets with PEDV. PEDV-specific IgG, IgA and neutralizing antibody (NA) responses were detected inORFV-PEDV-S-immunized and ORFV-PEDV-S-immunized/PEDV-exposed gilts. PEDV NA, IgG and IgA were detected inthe serum of piglets born to immunized gilts, demonstrating the transfer of antibodies through colostrum and milk. Pigletsborn to immunized gilts showed reduced morbidity and a marked reduction in mortality after PEDV challenge in comparisonto control piglets. Piglets born to gilts that received ORFV-PEDV-S and were exposed to live PEDV showed stronger NAresponses and lower clinical scores when compared to piglets born to gilts immunized with ORFV-PEDV-S alone. Theseresults demonstrate the potential of ORFV as a vaccine delivery platform capable of eliciting passive immunity against PEDV