Rapid Antigen-Capture Assay To Detect West Nile Virus in Dead Corvids

The utility of the VecTest antigen-capture assay to detect West Nile virus (WNV) in field-collected dead corvids was evaluated in Manitoba and Ontario, Canada, in 2001 and 2002.Swabs were taken from the oropharynx, cloaca, or both of 109 American Crows, 31 Blue Jays, 6 Common Ravens, and 4 Black-billed Magpies from Manitoba, and 255 American Crows and 28 Blue Jays from Ontario.The sensitivity and specificity of the antigen-capture assay were greatest for samples from American Crows; oropharyngeal swabs were more sensitive than cloacal swabs, and interlaboratory variation in the results was minimal.The sensitivity and specificity of the VecTest using oropharyngeal swabs from crows were 83.9% and 93.6%, respectively, for Manitoba samples and 83.3% and 95.8%, respectively, for Ontario birds.The VecTest antigen-capture assay on oropharyngeal secretions from crows is a reliable and rapid diagnostic test that appears suitable for incorporation into a WNV surveillance program. S ince 2000, surveillance for West Nile virus (WNV) indead corvids has been the cornerstone of the early warning system for this virus in the Canadian public health system.During 2001 and 2002, WNV was detected in avian tissues by using real-time TaqMan reverse transcription-polymerase chain reaction (RT-PCR), as described by Lanciotti et al. (1).Birds collected by local or provincial authorities were sent to regional centers for tissue collection.Tissue samples were shipped daily, often thousands of kilometers, to the National Microbiology Laboratory in Winnipeg, Manitoba, for final diagnosis (by RT-PCR).Though the sensitivity and specificity of TaqMan RT-PCR assay are excellent, the centralization of testing and the multiple steps necessary to extract bird tis-sues from carcasses, purify RNA, and screen samples for WNV genome presented major logistical, biosafety, reporting, and financial challenges.Komar et al. (2,3) demonstrated that WNV is present in high titer in oral and cloacal cavities of experimentally infected birds.Recently, a rapid antigen-capture wicking assay (VecTest, Medical Analysis Systems, Camarillo, CA) has become commercially available (4,5).Its use for screening swabs from the cloacal or oral cavities of dead birds has yet to be evaluated under field conditions.The ultimate goal of this study was to determine whether the VecTest assay could serve as a suitable alternative testing procedure for WNV dead bird surveillance.This goal was achieved by quantifying the sensitivity and specificity of this antigen-capture assay to detect WNV in corvids collected as part of routine dead bird surveillance programs in Manitoba and Ontario.The effect of storage conditions and duration of storage of swabs in grinding solution on the sensitivity of the assay and viability of virus was also assessed. Materials and MethodsCorvids collected as part of the WNV dead bird surveillance programs in Manitoba and Ontario, Canada, in 2001 and 2002 were used.Laboratories in each province received dead birds, collected oropharyngeal or cloacal swabs or tissues, performed the antigen-capture assay, and shipped tissues or swabs to the National Microbiology Laboratory for confirmatory testing.In both laboratories, only birds lacking signs of obvious decay or decomposition were included for testing.Birds typically were shipped to the laboratories via courier.During submission, most animals were held within insulated coolers containing freezer packs.If specimens could not be shipped on the date of collection, most were held at 4°C.On rare occasions, birds were frozen at -20°C by submitters before Rapid Antigen-Capture Assay To Detect West Nile Virus in Dead Corvids