Evaluation of the Efficacy of a Recombinant Adenovirus Expressing the Spike Protein of Porcine Epidemic Diarrhea Virus in Pigs

Liu, Xinsheng; Zhao, Donghong; Zhou, Peng; Zhang, Yongguang; Wang, Yonglu

Protecting suckling piglets through lactogenic immunity is dependent on the gut-mammary-sIgA axis [8] . e results here showed that there is a good correlation between the levels of serum IgG and IgA induced by rAd-PEDV-S and proved that the adenovirus vector construct is capable of eliciting humoral immunity and protection against PEDV infection in neonatal piglets. However, in the next study, rAd-PEDV-S should be used to immunize pregnant sows to determine whether it produces sIgA antibodies that are secreted in the colostrum and milk and ultimately transferred to suckling piglets (gut-mammary-sIgA axis). In this study, pigs from all four groups were challenged orally with 1 × 10 5 TCID 50 highly virulent genotype GIIb PEDV strain CH/HNPJ/2017 at 28 dpv. After the challenge, typical clinical signs of PEDV infection were observed in all four groups from 1 to 7 dpi. e results demonstrated that rAd-PEDV-S and the inactivated vaccine could markedly delay clinical signs, reduce virus shedding, and provide partial protection against the highly virulent PEDV challenge. e possible reasons for the low protective efficacy of rAd-PEDV-S and the inactivated vaccine in pigs are as follows: the inoculation dose in pigs in the challenge study was relatively higher than that in most of the previous PEDV animal experiments. Generally, most PEDV animal experiments use 100 TCID 50 virus as an inoculum. However, here, 1 × 10 5 TCID 50 highly virulent genotype GIIb PEDV strain was used as the inoculum in the pig challenge study. Although our previous study determined that the median pig diarrhea dose (PDD 50 ) of the challenge strain CH/HNPJ/ 2017 was 8.63 log 10 PDD 50 /3 mL at 7 dpi, the experimental animals were 4-day-old conventional suckling pigs [28] . erefore, the challenge inoculum dose in the present study cannot be completely in accordance with the previous PDD 50 . e results of this study indicated that a suitable inoculum dose is very important for a PEDV infection study and should be determined in advance in various ages of pigs.