Efficacy of an inactivated genotype 2b porcine epidemic diarrhea virus vaccine in neonatal piglets

Abstract

Massive outbreaks of porcine epidemic diarrhea virus (PEDV) recurred in South Korea in 2013-2014 and affected approximately 40% of the swine breeding herds across the country, incurring a tremendous financial impact on producers and consumers. Despite the nationwide use of commercially available attenuated and inactivated vaccines in South Korea, PEDV has continued to plague the domestic pork industry, raising concerns regarding their protective efficacies and the need for new vaccine development. In a previous study, we isolated and serially cultivated a Korean PEDV epidemic strain, KOR/KNU-141112/2014, in Vero cells. With the availability of a cell culture-propagated PEDV strain, we are able to explore vaccination and challenge studies on pigs. Therefore, the aim of the present study was to produce an inactivated PEDV vaccine using the KNU-141112 strain and evaluate its effectiveness in neonatal piglets. Pregnant sows were immunized intramuscularly with the inactivated adjuvanted monovalent vaccine at six and three weeks prior to farrowing. Six-day-old piglets born to vaccinated or unvaccinated sows were challenged with the homogeneous KNU-141112 virus. The administration of the inactivated vaccine to sows greatly increased the survival rate of piglets challenged with the virulent strain, from 0% to approximately 92% (22/24), and significantly reduced diarrhea severity including viral shedding in feces. In addition, litters from unvaccinated sows continued to lose body weight throughout the experiment, whereas litters from vaccinated sows started recovering their daily weight gain at 7 days after the challenge. Furthermore, strong neutralizing antibody responses to PEDV were verified in immunized sows and their offspring, but were absent in the unvaccinated controls. Altogether, our data demonstrated that durable lactogenic immunity was present in dams administrated with the inactivated vaccine and subsequently conferred critical passive immune protection to their own litters against virulent PEDV infection.

Keywords: Field isolate; Inactivated vaccine; Porcine epidemic diarrhea virus; Protective efficacy.

Fig. 1

Clinical significance scores in piglets from vaccinated (Gv) and unvaccinated (Gc) sows during the first 7 dpc. CSS was measured as described in Section 2. Error bars represent standard deviations. P values were calculated by comparing Gv and Gc groups using the Mann-Whitney U test. *, P = 0.001 to 0.05; †, P < 0.001.

Fig. 2

Survival rate of piglets from vaccinated (Gv) and unvaccinated (Gc) sows after challenge through 17 dpc.

Fig. 3

Average daily weight gain rate of piglets from vaccinated (Gv) and unvaccinated (Gc) sows after challenge through 17 dpc. Due to no piglets surviving after 9 dpc in the Gc group, daily weight gain could not be determined. Error bars represent standard deviations. P values were calculated by comparing Gv and Gc groups using the Mann-Whitney U test. *, P = 0.001 to 0.05; †, P < 0.001.