A novel chimeric vaccine candidate for porcine reproductive and respiratory syndrome virus (PRRSV) I and II elicits neutralizing antibodies against both types

Porcine reproductive and respiratory syndrome virus (PRRSV) is an economically important virus within the swine industry. The virus causes respiratory disease and reproductive failure. Two species of PRRSV-I and II are co-dominant, yet no effective vaccination strategy has been developed to protect against these two types. With an aim to develop a chimeric vaccine strain to protect against both types, in this study, a chimeric porcine reproductive and respiratory syndrome virus (PRRSV) type I and II was rescued using reverse genetics for the first time. Four chimeric infectious clones were designed based on the genomic arrangement of the structural proteins. However, only the clone carrying the transcriptional regulatory sequence (TRS) and ORF6 of a PRRSV-I and ORF6 of a PRRSV-II generated a viable recombinant virus, suggesting that concurrent expression of ORF6 from both parental viruses is essential for the recovery of type I and II chimeric PRRSV. The chimeric virus showed significantly lower replication ability than its parental strains in vitro , which was improved by serial passaging. In vivo , groups of pigs were inoculated with either the chimeric virus, one of the parental strains, or PBS. The chimeric virus replicated in pig tissue and was detected in serum 7 days post-inoculation. Serum neutralization tests indicated that pigs inoculated with the chimeric virus elicited neutralizing antibodies that inhibited infection with strains of both species and with greater coverage than the parental viruses. In conclusion, the application of this technique to construct a chimeric PRRSV holds promise for the development of a highly effective modified live vaccine candidate. This is particularly significant since there are currently no approved commercial divalent vaccines available to combat PRRSV-I and II co-infections.