DIRECT-DETECTION OF THE PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME(PRRS) VIRUS BY REVERSE POLYMERASE CHAIN-REACTION (RT-PCR)

A method for direct detection of the porcine reproductive and respirat ory syndrome (PRRS) virus was developed, based on reverse transcriptio n of the viral RNA coupled to DNA amplification by polymerase chain re action. A set of primers was designed from Lelystad virus sequence wit hin ORF 7 encoding nucleocapsid protein. From seven Spanish field isol ated strains the 312 bp amplified fragment was cloned and sequenced. A lignment with Lelystad virus sequence revealed a 96-97% homology. A ma ximum sensitivity of 6.7 TCID50 was achieved with the reported procedu re in experimentally infected swine alveolar macrophages cultures. The sensitivity obtained in crude clinical samples from experimentally in fected 3-weeks old pigs was approximately 10(2) TCID50. High specifici ty for the PRRS virus was demonstrated for the method, as none of the seven common swine virus assayed rendered DNA amplification product.