Location: Virus and Prion ResearchTitle: Sequence Stability of PRRSV Chimeras After Passage in Swine) Author
Submitted to: American Society for Virology Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 4/7/2010
Publication Date: 7/17/2010
Citation: Kappes, M.A., Ellingson, J.S., Wang, Y., Layton, S., Ciacci-Zanella, J.R., Roof, M.B., Faaberg, K.S. 2010. Sequence Stability of PRRSV Chimeras After Passage in Swine [abstract]. American Society for Virology Meeting. p. 269. Interpretive Summary:
Technical Abstract: Recombinant chimeric porcine reproductive and respiratory syndrome virus (PRRSV), generated from parental strains MN184 and a licensed modified live vaccine (Ingelvac® PRRS MLV), and a MN184 nsp2 deletion mutant were used to elucidate the mechanisms of attenuation and/or protective immunity to heterologous challenge in vivo. Chimeras rMN184ORF1/MLV, rMLVORF1/MN184, rMLV/MN184ORF5-6, rMLV/MN184ORF7-3'UTR, rMN184delta618, and rMLV/MN184-3'UTR were assessed alongside an attenuated MN184 strain (MN184-P102) and Ingelvac® PRRS MLV as vaccine treatment groups against heterologous challenge to PRRSV strain JA-142. Four vaccination groups, rMN184ORF1/MLV, rMLVORF1/MN184, rMLV/MN184ORF5-6, and MN184-P102 resulted in significant protection from heterologous challenge, as shown previously (Vaccine, 2010). To assess the stability of the vaccinations, nucleotide sequence analysis of approximately 4000 bases at the PRRSV 3'-end was completed on day 21 serum samples, which had shown different levels of viral growth at that time. Surprisingly, all chimeras were stable, with only a few nucleotide changes (< 1%) occurring in each swine-passaged virus when compared to the source sequence. The nucleotide changes were often silent, or represented degenerate sequence. The remaining amino acid alterations were mostly conservative in nature, and only one amino acid change was seen in more than one strain. Specifically, GP4 amino acid 114 was mutated from a valine to a leucine in all chimeras that possessed MLV parental sequence. The ramifications of this change are not known. Taken together, the data suggests that the chimeras were relatively stable, and did not quickly alter their genomic sequence in order to increase their replication rate in swine.