Porcine epidemic diarrhea virus (PEDV) was first detected in the US in 2013. After its introduction, PEDV rapidly spread throughout the country, causing the deaths of over 7 million piglets and resulting in significant economic losses to the swine industry. The major factors that contributed for the rapid spread of PEDV in the US were the lack of vaccines and the limited knowledge regarding pathways of transmission and dissemination. A little over a year after the first detection of PEDV, two vaccines received conditional license from the USDA and are available to pork producers in the country. However, the efficacy of these vaccines in the field, is still unknown.
In the 2015 the National Pork Board requested proposals for the development of novel vaccine strategies for Swine enteric coronavirus disease targeting PEDV and PDCoV. The goal of the project that we proposed was to develop a vector vaccine delivery platform to control SECD in swine.
Objective 1: To develop a poxviral-vector encoding the spike proteins of porcine epidemic diarrhea virus.
Objective 2: To assess the immunogenicity and protective efficacy of the poxviral vectored PEDV vaccine candidate in pigs.
By using the parapoxvirus Orf virus (ORFV) as our vaccine delivery platform, we developed a recombinant virus expressing the PEDV spike (S) protein. The S protein of PEDV is the main target of neutralizing antibodies against PEDV, therefore representing a good candidate for vaccine development. Initially, we tested our recombinant ORFV-PEDV-S candidate in 3-week-old weaned piglets focusing on assessing its ability to induce immune responses in immunized animals and in conferring protection against oral PEDV infection. Results from this pilot study demonstrated that the ORFV-PEDV-S was capable of eliciting immune responses in vaccinated pigs and to protect against clinical signs of PED. Additionally, animals immunized with the recombinant ORFV-PEDV-S vaccine candidate, excreted lower amounts of virus in the environment.
The ultimate goal of our research was to evaluate the capability of the ORFV-PEDV-S vaccine candidate to induce lactogenic immunity in piglets born to vaccinated pregnant gilts. PEDV negative gilts received three doses of the ORFV-PEDV-S vaccine candidate during pregnancy (3-week intervals) with the last dose being administered 2 weeks prior to farrowing. One the two groups immunized with the ORFV-PEDV-S candidate was also exposed to live PEDV orally on day 31 post immunization, after the second dose of the vaccine candidate. Serological responses induced by immunization were assessed in the serum, colostrum and milk of immunized gilts. Additionally, transfer of immunity from immunized dams to their piglets was evaluated by measuring PEDV specific antibodies in serum of these piglets. The protective efficacy of the vaccine candidate was also evaluated by challenge infection studies of the piglets on day 7 post-birth.
Interestingly, results from these studies showed that immunization of pregnant gilts with ORFV-PEDV-S results in immune responses to PEDV that are transferred to piglets through colostrum and milk. The resultant immunity provides partial protection to piglets born to immunized gilts as evidenced by reduced mortality rates in immunized groups when compared to control animals. Additionally, piglets born to immunized gilts presented lower clinical scores when compared to those born to non-immunized control gilts.
Contact information: Diego G. Diel
Box 2175 North Campus Dr
South Dakota State University
Brookings, SD 57007