Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2007
Publication Date: 2/20/2008
Citation: Wang, Y., Liang, Y., Han, J., Burkhart, K.M., Vaughn, E.M., Roof, M.B., Faaberg, K.S. 2008. Attenuation of porcine reproductive and respiratory syndrome virus strain MN184 using chimeric construction with vaccine sequence. Virology. 371(2):418-429. Interpretive Summary: Porcine reproductive and respiratory syndrome virus (PRRSV) causes a swine disease that is of great economic concern. Present vaccines against PRRSV are not ideal due in part to the heterogeneous nature of the virus. In order to test whether the replicase protein or the structural proteins of the virus were primarily responsible for virulence, we produced two artificial viruses - one of a PRRSV strain (MN184) causing severe disease and one to a vaccine strain (Ingelvac). The artificial viruses were shown to directly mimic the original PRRSV strains. Then we developed chimeras, one representing the replicase gene of the vaccine strain and the structural proteins of MN184, and the other of the opposite gene configuration. We determined that both chimeric constructs had intermediate phenotypes in vitro, and in vivo analysis found the both were attenuated compared to MN184. Thus, both parts of the genome contribute in some manner to the overall virulence. In addition, the strategy we employed could be utilized to rapidly prepare vaccines against emerging PRRSV strains. The results will be used by scientists to produce vaccine constructs and to increase their knowledge of why PRRSV causes disease. The downstrean impact on swine producers, industry and the general public will be a better and safer vaccine for less cost.
Technical Abstract: Two genetically distinct infectious recombinant virus clones (pMLV, constructed from Ingelvac(R) PRRS MLV and pMN184, constructed from virulent strain MN184) were developed to study attenuation of contemporary porcine reproductive and respiratory syndrome virus (PRRSV) strain MN184. Two reciprocal chimeric clones (pMLVORF1/MN184 and pMN184ORF1/MLV) were then constructed, such that the 5'UTR/ORF1 of one genotype was linked to ORF2-7/3'UTR from the other genotype. In vitro studies demonstrated that the rescued chimeric viruses possessed intermediate growth properties compared to recombinant rMLV and rMN184. Swine inoculation with rMN184 and rMLV verified that these viruses fully mimicked the respective parent virus. In addition, earlier and higher antibody responses were detected in animals infected with rMN184 in contrast to those infected with rMLV. Chimeric virus treatment groups showed similar antibody responses as seen with these parent viruses, but much less severe pathogenesis when compared to the rMN184 group. These data suggested that genetic aspects of Ingelvac(R) PRRS MLV 5'UTR/ORF1 replicase region and/or the structural proteins/3'UTR can serve to attenuate virulent strain MN184. The data also indicated that designed PRRSV vaccines could be developed, keeping the known 5'UTR/replicase region of an early vaccine strain such as Ingelvac(R) PRRS MLV intact, but replacing the structural protein/3'UTR domain with that of an emerging virulent virus.