Patent ID: 8492533

Claim:
An isolated polynucleotide molecule comprising a DNA sequence encoding an infectious RNA molecule encoding a North American PRRS virus wherein said DNA sequence is SEQ ID NO:1, or a sequence that has at least 70% identity to SEQ ID NO:1, or that hybridizes to the complement of SEQ ID NO:1 under highly stringent conditions which comprise hybridization to filter bound DNA in 0.5M NaHPO 4 , 7% SDS, 1 mM EDTA at 65° C., and washing in 0.1×SSC/0.1% SDS at 68° C., wherein said molecule lacks at least one DNA sequence encoding a detectable antigenic epitope of North American PRRS virus in the nonstructural protein 2 coding region of ORF1a within said DNA sequence, and wherein said isolated polynucleotide molecule does not comprises a nucleotide sequence, within said PRRS encoding sequence, that encodes a detectable heterologous antigenic epitope.