Evaluation of Unexpected Positive Results from a Commercial ELISA for Antibodies to PRRSV

May 28, 2009 — 

Unexpected positive results from the widely used IDEXX ELISA for the detection of antibodies to porcine reproductive and respiratory syndrome virus (PRRSV) may confound investigations of the disease. Supplementing the ELISA with blocking agents and the use of IgG purified from serum samples had no effect on the unexpected positive results, suggesting that they were due to an antibody-antigen reaction. Simple competitive and blocking ELISAs were developed by modifying the IDEXX ELISA, and they and an indirect fluorescent antibody test (IFAT) were used to examine PRRSV antibodies in 33 antibody-negative, 88 antibody-positive and 73 unexpectedly positive sera. All the unexpectedly positive sera were negative by IFAT, and 89.0 percent were negative by both the competitive and blocking ELISAs. The competitive ELISA (97.7 percent) and the blocking ELISA (96.5 percent) detected more positive sera than the IFAT (90.9 percent). These results show that both ELISAs are capable of distinguishing positive and unexpectedly positive sera, and suggest that most of the unexpected positive signals are false-positives.

Okinaga T, Yamagishi T, Yoshii M, Suzuki T, Miyazaki A, Takagi M, Tsunemitsu H, Evaluation of unexpected positive results from a commercial ELISA for antibodies to PRRSV, Vet Rec. 2009 Apr 11;164(15):455-9.

Viral Diseases Research Team, National Institute of Animal Health, Kannondai, Tsukuba, Ibaraki 305-0856, Japan.