Abstract

We tested 343 dead birds of 58 species for West Nile virus (WNV) infection from mid-July to September 2003 at the Centers for Disease Control and Prevention in Fort Collins, Colorado. The vast majority of bird carcasses tested were from Colorado (19 counties), with a relatively small number of birds from Wyoming (2 counties) and Nebraska (3 counties). The sample set consisted of dead birds found by the public, as well as birds that died or were euthanatized at wildlife rehabilitation centers. The gold-standard test in our study was TaqMan RT-PCR of heart samples with two sets of primers. Additional tests included VecTest™ WNV Antigen Assay of oral swabs and plaque assay of heart samples. Thirty-two percent of birds tested positive by TaqMan RT-PCR of heart; concurrent experimental evaluation of VecTest™ WNV Antigen Assay of oral swab indicated an overall sensitivity of 70%. When birds were separated into groups, VecTest™ sensitivities were 85% (n=60) for corvids, 44% (n=27) for raptors, and 62% (n=26) for other (non-corvid, non-raptor) bird species. The sensitivity of plaque assay of heart tissue was 89% as compared to TaqMan RT-PCR of heart tissue, with 88% sensitivity for corvids, 89% for raptors, and 92% for other species. We recognize that none of these tests are 100% sensitive for WNV, but based on our results, we believe that VecTest™ WNV antigen assay of oral swab is a reasonable test for use in corvids, and plaque assay is a relatively useful test in all bird species to detect the presence of WNV when RT-PCR is not available. Our results may be useful for WNV surveillance as well as diagnostic purposes.