Development of DNA vaccine against porcine epidemic diarrhea virus

Abstract

Porcine epidemic diarrhea (PED) is a devastating enteric disease mainly affected to the sucking piglets which causing the severe economic losses in many countries worldwide including Thailand. To date, there have no satisfied commercial vaccine for PED. The clustering system based on the spike gene demonstrated 2 variant of PEDV, classical and pandemic variant, which the difference of these variants may be affected to the protective immunity between them. The objectives of this study were to investigate the genetic diversity of S gene of PEDV in Thailand and evaluate the efficacy of DNA vaccine which developed from Thai PEDV isolate. In this study, the nucleotide and amino acid sequence of S gene of Thai isolates PEDV were analyzed with isolates from other countries. The results demonstrated Thai PEDV isolates were belong to the pandemic variant which the neutralizing epitope of these isolates were different to the vaccine isolate. In addition, insertion and deletion at N-terminal of S gene were detected in these Thai isolates. To develop the DNA vaccine against PEDV, plasmid DNA was constructed and the vaccine efficacy was evaluated in weaned pigs and gestation gilts. Humoral and cellular immunity were investigated by viral neutralization assay, ELISA, lymphocyte proliferation and detection of IFN-g producing cells. The results demonstrated the absence of PEDV-specific antibody in all groups but the lymphocyte proliferation of CD4+ cell at 7 DPV and the PEDV-specific IFN-g producing cell of CD4+ and CD8+ cells at 28 DPV in vaccinated pigs was higher than control pigs (p<0.05). Meanwhile, the PEDV-specific IgA and the neutralizing antibody titer in colostrum and milk of vaccinated sows were relatively higher than control group which might be associated with the booster effect. This study reveal the possibility of the DNA vaccine to be a vaccine candidate which might be used in the control and prevention program