Evaluation of porcine epidemic diarrhea virus transmission and the immune response in growing pigs

Authors: CRAWFORD, KIMBERLY - Orise Fellow; Lager, Kelly; Miller, Laura; OPRIESSNIG, TANJA - Iowa State University; PRISCILLA GERBER, PRISCILLA - Roslin Institute; HESSE, RICHARD - Kansas State University

Submitted to: Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2015
Publication Date: 5/6/2015
Citation: Crawford, K., Lager, K., Miller, L., Opriessnig, T., Gerber, P., Hesse, R. 2015. Evaluation of porcine epidemic diarrhea virus transmission and the immune response in growing pigs. Veterinary Research. 46(1):49.

Interpretive Summary: In 2013, porcine epidemic diarrhea virus (PEDV) emerged in the United States with devastating impact on the swine industry. Within the first year the virus spread through half of the US swine herds causing an estimated 5-7% loss in pigs nationwide. PEDV causes severe diarrhea in baby pigs causing almost 100% mortality up to several weeks of age. As pigs get older they become less susceptible to the virus. Control of PEDV will be dependent on understanding how the virus transmits among swine, and how the pig's immune system responds to infection and possible vaccination. To study these areas, a pig model was developed to evaluate the duration of virus shedding, and characterize the immunity following infection. Young pigs were "naturally" infected by exposure to a pig experimentally infected with PEDV grown in cell culture. The naturally infected pigs developed mild-to-moderate diarrhea for 4-7 days, but otherwise were not seriously affected. Although rectal swab samples collected from the pigs were positive by a commonly used diagnostic test up to 42 days post challenge, infectious virus was only detected in the pigs up to about 2 weeks post exposure. To test the development of protective immunity in the naturally infected pigs, the pigs were given an oral exposure to cell-culture grown virus. The challenge did not result in re-infection of the pigs, suggesting they had developed immunity from the original infection. This young pig model was successful for demonstrating that infected pigs could shed infectious virus for 2 weeks post infection, and pigs could develop a protective immune response indicating the potential of using this model to evaluate PEDV vaccines.

Technical Abstract: Clinical disease associated with porcine epidemic diarrhea virus (PEDV) infection in naïve pigs is well chronicled; however, information on endemic PEDV infection is limited. To characterize chronic PEDV infection, the duration of infectious virus shedding and development of protective immunity was determined. On Day 0 (D0), a growing pig was challenged with PEDV and 13 contacts were comingled. On D7, 9 contact pigs (principal virus group (PG)), were selected, moved to a separate room and comingled with one sentinel pig (S1). This process was repeated weekly with S2, S3 and S4. The PG was PEDV-positive by PCR from D3-11, with some pigs intermittently positive to D42. Pigs S1 and S2 were PEDV-positive within 24 hours of comingling. Antibodies were detected in all PG by D21 and by 7 days post-contact in S1 and S2. Pigs S3 and S4 were PCR and antibody negative following commingling. To evaluate protective immunity, 5 naive pigs (N) and the PG were challenged (N/C, PG/C) with homologous virus on D49. All N/C pigs were PEDV PCR-positive by D52 with detection out to D62 in 3/5 N/C pigs. All PG/C pigs were PEDV PCR-negative post-challenge. By D63, all N/C seroconverted. Although PEDV RNA was demonstrated in pigs after primary infection until D42, infectious PEDV capable of horizontal transmission to naïve pigs was only shed 14-16 days after infection to age-matched pigs. Homologous re-challenge 49 days post initial PEDV exposure did not result in re-infection of the pigs. This demonstrates potential for an effective PEDV vaccine.