ARS | Publication request: Sequence and virulence comparison of four North American isolates of porcine reproductive and respiratory syndrome virus

Submitted to: Conference Research Workers Disease Meeting
Publication Type: Abstract Only
Publication Acceptance Date: September 26, 2011
Publication Date: December 4, 2011
Citation: Brockmeier, S.L., Loving, C.L., Miller, L.C., Vorwald, A.C., Kehrli, Jr., M.E., Baker, R.B., Nicholson, T.L., Lager, K.M., Faaberg, K.S. 2011. Sequence and virulence comparison of four North American isolates of porcine reproductive and respiratory syndrome virus. Conference of Research Workers in Diseases. Paper No. 174. p. 171.

Technical Abstract: Considerable genetic, antigenic and virulence differences exist among porcine reproductive and respiratory syndrome virus (PRRSV) isolates and depending on strain, dose and immune status, some farms may be subclinically infected with PRRSV while others experience severe reproductive and/or respiratory disease. In this study, we compared the genomic sequence and virulence of 4 North American Type 2 PRRSV isolates, two pathogenic isolates that were associated with the emergence of novel and/or atypical PRRSV outbreaks in the late 1990's to early 2000's (SDSU73 and MN184) and two contemporary isolates of unknown pathogenicity and virulence (NADC30 and NADC31). Among the 4 isolates, SDSU73, MN184, and NADC30 were all clearly more virulent than NADC31, and among the 3 more virulent isolates, SDSU73 appeared to be the most virulent based on lung lesions, lymphadenopathy, febrile response, and decreased weight gains. Viral titers in the lung lavage and serum were highest for pigs infected with SDSU73 and MN184, and these were statistically greater than viral titers for pigs infected with the NADC31 isolate of PRRSV. Pigs infected with the NADC30 isolate had viral titers between those of pigs infected with either SDSU73 or MN184 and those of pigs infected with NADC31. Lesions consistent with bacterial bronchopneumonia were present to varying degrees only in pigs infected with PRRSV, and bacteria typically associated with the porcine respiratory disease complex were isolated from the lung of these pigs. Cytokine levels in the lung lavage were evaluated by multiplex ELISA and results show an increased production of several cytokines in pigs infected with PRRSV, but to varying degrees depending on the PRRSV isolate with which the pigs were infected. Genomic sequence evaluation indicates that both the NADC30 and NADC31 isolates of PRRSV maintain the nonstructural protein 2 deletion seen in MN184, but NADC31 has two additional 15 and 36 nucleotide deletions, and these strains are 8-14% different on a nucleotide basis from the MN184 strain. Combined with the differing levels of attenuation, these results indicate specific genomic determinants of virulence are elusive and almost certainly complex.