DIFFERENTIATION OF A PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS-VACCINE STRAIN FROM NORTH-AMERICAN FIELD STRAINS BY RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISM ANALYSIS OF ORF-5

The suitability of restriction fragment length polymorphism (RFLP) ana lysis for differentiating a porcine reproductive and respiratory syndr ome virus (PRRSV) vaccine strain from other North American field strai ns was investigated. Open reading frame 5 nucleotide sequence data of the vaccine virus, its parent strain VR-2332, and 22 other strains of PRRSV included in this study indicated that 3 restriction enzyme gel p atterns characterize the vaccine virus and the parent strain genotype. The combined 3 RFLP patterns differentiate the vaccine and parent vir us from other PRRSV strains. This test will be a valuable tool in epid emiologic studies and will be useful in identifying individual strains in cases of multistrain PRRSV infections.