A heterologous 'prime-boost' anti-PEDV immunization for pregnant sows protects neonatal piglets through lactogenic immunity against PEDV

Abstract

Porcine epidemic diarrhoea virus (PEDV) causes severe diarrhoea in neonatal suckling piglets with a high mortality. Maternal vaccines that can induce lactogenic immunity to protect suckling piglets via colostrums and milk are pivotal for the prevention and control of PEDV infection in neonatal suckling piglets. In this study, a group of pregnant sows were first orally immunized with coated PEDV-loaded microspheres and boosted with killed PEDV vaccines (heterologous prime-boost). It has been detected that the levels of PEDV-specific antibodies (IgG and IgA) in their sera and milks were higher than other negative groups (P < 0·001 or P < 0·05). Furthermore, it has been proved by the neutralization assay that the induced antibodies could significantly inhibit virus infection as compared to other negative groups (P < 0·01 or P < 0·05). Importantly, after PEDV challenge, more than 90% of the suckling piglets delivered by the sows in the heterologous prime-boost group were completely protected. Overall, the results show that 'heterologous prime-boost' form is an efficient and effective way to provide protection for suckling piglets against PEDV through lactogenic immunity. SIGNIFICANCE AND IMPACT OF THE STUDY: As a widespread swine pathogen, PEDV affects the swine industry enormously. It causes enteritis in swine of all ages and is often fatal in neonatal piglets. Our data show that pregnant sows were immunized with 'coated PEDV-loaded microspheres + killed PEDV vaccines' (heterologous prime-boost immunization) could protect more than 90% suckling piglets delivered by the sows against the virus. These findings provide a new model of developing safe and effective immunizations for newborn animals against established and emerging enteric infections.

Keywords: coated PEDV-loaded microspheres; heterologous prime and boost; pig; porcine epidemic diarrhoea virus (PEDV); vaccine.

Figure 1

Specific anti‐PEDV antibody titres in the serum and milk collected from pregnant sows after prime‐boost immunizations. (a) Serum was collected from the pregnant sows of all groups on days 0, 21 and 35 post first immunization, and was assayed for anti‐PEDV‐specific IgG antibodies through ELISA. (b) Milk was collected from the pregnant sows of all groups on day 1 postfarrowing and was assayed for anti‐PEDV‐specific IgA antibodies through ELISA. Data are represented as mean ± SD, n = 5. * stand for P < 0·05, and *** stand for P < 0·001. Groups: (○) DMEM + DMEM; (△) PEDV + PEDV; (□) coated PEDV‐loaded microspheres + coated PEDV‐loaded microspheres; (●) PEDV + inactivated PEDV vaccines; (▲) coated PEDV‐loaded microspheres + inactivated PEDV vaccines; (■) inactivated PEDV vaccines + inactivated PEDV vaccines

Figure 2

Neutralizing antibody titres in the serum and milk collected from the pregnant sows after prime‐boost immunizations. (a) Serum was collected from the pregnant sows of all groups on day 35 post first immunization and (b) milk was collected on day 1 postfarrowing and their neutralizing antibody titres were analysed. Neutralizing antibody titres were expressed as dilutability at 50% inhibition of PEDV infection in Vero cells. Data are represented as mean ± SD, n = 5. ** stand for P < 0·01 and * stand for P < 0·05. Groups: (○) DMEM + DMEM; (△) PEDV + PEDV; (□) coated PEDV‐loaded microspheres + coated PEDV‐loaded microspheres; (●) PEDV + inactivated PEDV vaccines; (▲) coated PEDV‐loaded microspheres + inactivated PEDV vaccines; (■) inactivated PEDV vaccines + inactivated PEDV vaccines

Figure 3

Protection efficacy of the prime‐boost immunizations in suckling piglets against the challenge of PEDV. Pregnant sows were first orally immunizated with attenuated PEDV vaccines or coated PEDV‐loaded microspheres or intramuscular injected with inactivated PEDV vaccines, and boosted with attenuated PEDV vaccines or coated PEDV‐loaded microspheres or inactivated PEDV vaccines, and the control group was orally inoculated with maintenance medium in the ‘prime‐boost’ form. All neonatal suckling piglets were orally challenged with a PEDV strain on the seventh day after delivery. The mortality rate of suckling piglets in different immunizated groups was recorded daily from the first day to the 10th day after challenge for protection rate analysis. Data are represented as mean ± SD, n = 5. Groups: (○) DMEM + DMEM; (△) PEDV + PEDV; (□) coated PEDV‐loaded microspheres + coated PEDV‐loaded microspheres; (●) PEDV + inactivated PEDV vaccines; (▲) coated PEDV‐loaded microspheres + inactivated PEDV vaccines; (■) inactivated PEDV vaccines + inactivated PEDV vaccines