Impact of Porcine Epidemic Diarrhea Virus (PEDV) subunit vaccine in endemically infected breeding herd in North America

The objective of this study was to evaluate the efficacy of a sub-unit PEDV vaccine (Harris Porcine Epidemic Diarrhea Vaccine, RNA®) in an endemically infected breeding herd that had experienced elevated pre-weaning mortality (40-60%) for 26 weeks.

On May 4, 2014 a 2,500 head breeding farm reported watery diarrhea and vomiting in 7-day-old piglets. Samples were negative for TGE, but positive for PEDV by PCR. Sequencing of the S1 region (2.2kb) indicated it was 99% similar to the strains circulating the U.S. Whole herd feedback (affected piglet intestines) was initiated and all adult animals on the farm received the inoculum twice in the first week of the outbreak. No gilts were entered for 6 months and were given the same oral PEDV inoculum (feedback) 10 weeks prior to entry to the breeding herd. All pigs older than 12 days were weaned early and any new pigs being born were euthanized for a 3 week time period. McREBEL movement restrictions were put into place. All farrowing rooms were cleaned, disinfected and dried prior to loading new sows. Despite these changes, the herd continued to see PEDV-related diarrhea at 2-3 days of age and pre-weaning mortality continued at 40-60% even out to 6 months later. On October 29th, the farm initiated a single pre-farrow vaccination program, where dams were vaccinated with the PEDV vaccine 7-14 days prior to farrowing (per label).

The first week the vaccinated dams farrowed, a dramatic reduction was seen in both % of litters showing clinical signs as well as pre-weaning mortality during the first 7 days. The first group of pigs weaned from vaccinated dams saw a 200% reduction in pre-wean mortality from the week prior. Within 5 weeks, the farm could no longer find evidence of PEDV infection by PCR on suckling piglets that were being tested on a weekly basis (n=20). A statistical analysis, using a GLM procedure in ANOVA, was run comparing the 14 weeks prior to the initiation of the vaccine program (control) to the 14 weeks following initiation of the vaccination program (treatment). With each group having approximately 1400 litters, the pre-weaning mortality of the control group was 64.4% and the pre-weaning mortality of the treatment group was 23.1% (p< .001). Baseline pre-wean mortality prior to break was 18%.

Despite extreme efforts in feedback, cleaning and sanitation, clinical signs and elevated mortality persisted in this endemically infected breeding herd. It wasn’t until a sub-unit vaccine was applied in a pre-farrow protocol, with intent to booster secretory IgA, was there a significant reduction in clinical signs and mortality in suckling pigs.

Disclosure of Interest: None Declared.