The Rescue and the Selection of the Thermally Stabled Type O Vaccine Candidate Strains of Foot-and-mouth Disease Virus

Abstract The inactivated vaccines of Foot-and-mouth disease virus (FMDV) have been used widely in the world to control Foot-and-mouth disease (FMD). But the virions (146S) of this virus are easily dissociated into pentamer subunits (12S), thus limits the immune protective efficacy of the inactivated vaccines when the temperature is higher than 30°C. The cold-chain system can maintain the quality of the vaccines, but that is usually not reliable in limited resource settings. Thus, it is imperative to improve the thermostability of vaccine strains to guarantee the vaccines’ quality. In this study, 4 recombinant FMDV strains containing single or multiple amino acids substitutions in the structural proteins (SP) were rescued by using a pre-constructed FMDV type O full-length infectious clone (pO/DY-VP1). The assays used here indicated that the single or multiple amino acids substitutions in SP may affect the viral replications to different degrees. Furthermore, the heat and acid stabilities of the recombinant viruses were significantly improved comparing with the parental virus. Three well thermally stable strains of recombinant viruses (rHN/DY-VP1Y2098F, rHN/DY-VP1V2090A-S2093H and rHN/DY-VP1V2090A-S2093H-Y2098F) were selected for inactivated vaccine to immunize pigs. Blood samples were collected every week to prepare sera. Meanwhile the effects of mutations in SP amino acids on the antigenicity were analyzed by viral neutralization test, which showed that the substitutions of S2093H, Y2098F and S2093H-Y2098F did not affect the immunogenicity. In addition, comparing to the parental virus, Y2098F mutation could increase the thermostability significantly (p<0.05). In conclusion, the rHN/DY-VP1Y2098F mutant is considered as a potential vaccine strain in the future.