Evaluation of commercial assays for detecting West Nile virus antigen.

Two commercially available West Nile virus (WNV) detection assays (RAMP WNV test, Response Biomedical Corp., Burnaby, British Columbia, Canada; and VecTest WNV antigen assay, Medical Analysis Systems, Inc., Camarillo, CA) were compared for sensitivity, specificity, and ability to detect WNV in field-collected mosquito pools. Serially diluted stock seed WNV and St. Louis encephalitis virus (SLEV) were used to determine sensitivity and specificity. The RAMP WNV test detected WNV at concentrations as low as 3.17 log10 plaque-forming units per milliliter (PFU/ml), whereas the VecTest assay detected WNV at concentrations as low as 5.17 log10 PFU/ml. Neither test cross-reacted with SLEV. A WNV-specific reverse transcriptase polymerase chain reaction was used to identify positives among field-collected mosquito pools. The RAMP WNV test detected 94% of positive pools and the VecTest assay detected 65% of the positive field-collected pools. Despite these differences, both assays have characteristics that make them useful in WNV surveillance programs.