Porcine reproductive and respiratory syndrome has been devastating the swine industry since the late 1980s. The disease has been controlled, to some extent, through the use of modified live-attenuated (MLV)
vaccines once available. However, such a practice periodically resulted in isolation or detection of
vaccine-like viruses from pigs as determined by a partial genomic sequencing. In this study, we developed a heteroduplex mobility assay (HMA) for quickly identifying porcine reproductive and respiratory syndrome virus (PRRSV) isolates with significant nucleotide sequence identities (>/=98%) with the modified live-
attenuated vaccines. The major envelope gene (ORF5) of 51 PRRSV field isolates recovered before and after the introduction of the
vaccines was amplified, denatured, and reannealed with the HMA reference
vaccine strains Ingelvac
PRRS MLV and Ingelvac
PRRS ATP, respectively. Nine of the 51 field isolates and the VR2332 parent virus of Ingelvac
PRRS MLV, which were all highly related to Ingelvac
PRRS MLV with </=2% nucleotide sequence divergence as determined by sequence analysis, were all identified by the HMA to form homoduplexes with the reference Ingelvac
PRRS MLV. No homoduplex-forming field isolate was identified when Ingelvac
PRRS ATP was used as the HMA reference except for its parent virus JA142. Other field isolates with more than 2% nucleotide sequence divergence with the respective reference
vaccine strain resulted in the formation of heteroduplexes with reduced mobility in
polyacrylamide gel electrophoresis. The HMA results also correlated well with the results of phylogenetic analyses. The data indicated that the HMA developed in the study may be a rapid and efficient method for large-scale screening of potential
vaccine-like PRRSV field isolates for further genetic characterization.