Date Full Report Received12/15/2008
Date Abstract Report Received12/15/2008
Funded ByNational Pork Board
Enormous genetic and antigenic variation impedes effective control and prevention of PRRS. Since PRRS virus vaccination is shown to be effective only against homologous or closely related viruses, development of a vaccine which can provide broad cross-protection against various PRRS viruses has become essential for PRRS eradication in the future. A previous study in our laboratory revealed that the significance of PRRS virus structural genes [i.e. open reading frames (ORFs) 3, 5, and 6] in cross-neutralization and their roles in protective immunity could be variable for different PRRS viruses. Our previous study also suggested that chimeric PRRS viruses generated by combining structural genes from two distinct PRRS viruses (i.e. VR2332 and JA142) in an organized manner can induce virus neutralizing antibody against both viruses. Therefore, we hypothesized that those chimeric PRRS viruses could confer broader cross-protection against the challenge of those two distinct PRRS viruses when pigs are vaccinated with the live chimeric viruses. To test the hypothesis, 114 PRRS virus-free pigs were purchased, housed in 6 different rooms, and vaccinated with either sham inoculum, two wild-type viruses (VR2332 and JA142), or one of three chimeric mutants: ORF 5, ORFs 5 and 6, or ORFs 2-6 were substituted with the corresponding gene(s) of JA142 to construct JAP5, JAP56, and JAP2-6, respectively, while the remaining virus genome used intact VR2332 sequence. At 44 days post inoculation (dpi), the pigs were challenged with either VR2332 or JA142. The pigs were bled every week until 72 dpi and necropsied at 58 dpi and 72 dpi for pathological evaluation. Pigs inoculated with chimeric PRRS viruses prior to the virus challenge produce a significantly lower level of viremia after being challenged with both VR2332 and JA142 as compared to the other groups. No significant lesion was found in the lungs from the pigs previously inoculated with the chimeric viruses after the challenge although only mild to moderate lesions were observed in the virus challenge control groups. In conclusion, these observations suggest that inoculation with a live chimeric PRRS virus can confer broader cross-protection against two different PRRS viruses, and JAP56 chimeric mutant virus is a good vaccine candidate to prevent the infection by both VR2332 and JA142. Further study remains to determine if this concept is applicable for other PRRS virus strains.