Diagnostic performance of assays for the detection of anti-Porcine reproductive and respiratory syndrome virus antibodies in serum and muscle transudate ("meat juice") based on samples collected under experimental conditions

Three assays were evaluated for their ability to detect antibodies against Porcine reproductive and respiratory syndrome virus (PRRSV) in porcine muscle transudate ("meat juice") samples. Samples were derived from 91 pigs inoculated with PRRSV isolate VR-2332 and 46 age-matched controls. Serum and muscle (Musculus longissimus dorsi) samples were collected from randomly selected animals euthanized at ∼ 14-day intervals from 28 to 202 days postinoculation. Serum samples were assayed at a dilution of 1:40, and muscle transudate samples were assayed at 5 dilutions (1:2, 1:5, 1:10, 1:20, 1:40) using a commercial PRRSV antibody enzyme-linked immunosorbent assay (ELISA). In addition, muscle transudate samples were tested using an indirect fluorescent antibody test (IFAT) at 5 dilutions (1:2, 1:5, 1:10, 1:20, 1:40). Attempts to assay muscle transudate samples for neutralizing antibodies using a modified fluorescent focus neutralization assay were unsuccessful. Receiver operator characteristic (ROC) curve analyses were used to estimate cutoff thresholds and the associated diagnostic sensitivities and specificities for ELISA and IFAT at each dilution. For ELISA, muscle transudate samples at the ROC-optimized cutoffs were >95% sensitive and 100% specific at each dilution. At a cutoff dilution of ≥ 1:5, the IFAT diagnostic sensitivity and specificity of muscle transudate was estimated at 63.3% and 100%, respectively. These findings validated the use of muscle transudate samples in PRRSV surveillance programs based on ELISA antibody testing.