The reverse transcription polymerase chain reaction for the diagnosis of porcine reproductive and respiratory syndrome: comparison with virus isolation and serology.

A single-tube reverse transcription polymerase chain reaction (RT-PCR) assay for the detection of porcine reproductive and respiratory syndrome (PRRS) virus in blood samples from infected pigs was developed. This test was assessed for sensitivity and application as a rapid diagnostic tool by comparison with virus isolation and detection of PRRS virus antibody in blood. The RT-PCR test was slightly more sensitive than virus isolation for detection of virus in serum and markedly more sensitive than virus isolation from plasma from experimentally infected pigs. The RT-PCR test was also applicable when using whole blood-impregnated filter paper discs, with 94% of the specimens taken by this procedure being positive when compared to RT-PCR performed on serum. PRRS viral nucleic acid was detected in blood samples as early as 24 h after infection and persisted for some time, whereas circulating antibody to PRRS virus was not detected in the same animals until 9 days after infection. These results indicate that the RT-PCR may be an useful technique for the early identification of PRRS viral nucleic acid in blood samples of infected pigs.