DEVELOPMENT AND EVALUATION OF A NON-ISOTOPICALLY LABELED DNA-PROBE FOR THE DIAGNOSIS OF INFECTIOUS LARYNGOTRACHEITIS

A digoxigenin-labeled cloned infectious laryngotracheitis virus (ILTV) DNA fragment was evaluated as a nonradioactive alternative probe in t he diagnosis of infectious laryngotracheitis. The dot-blot hybridizati on protocol was optimized and was capable of detecting 40 pg of purifi ed ILTV DNA and as few as 50 ILTV-infected chicken embryo liver cells. The utility of this approach for diagnostic use was evaluated through four ILTV inoculation trials using a mild field isolate, a virulent c hallenge strain, a tissue-culture-origin vaccine, and an egg-origin va ccine. Birds were examined for clinical signs of ILT, and conjunctival and pharyngeal swabs from inoculated and sentinel birds were tested f or ILTV by the digoxigenin-labeled probe and by virus isolation. In ge neral, higher numbers of ILTV-positive samples were detected by both a ssays from conjunctival swabs. For the non-vaccine strains, detection by dot-blot hybridization was equivalent to that for virus isolation. However, for the two vaccine strains, there was some lack of correlati on between the dot-blot results and the virus-isolation results. The k appa values between virus-isolation results and dot-blot results for t he tissue-culture-origin vaccine, egg-origin vaccine, Ont 1598 field i solate, and virulent strain were 0.00, 0.16, 0.39, and 0.24, respectiv ely, for pharyngeal samples and 0.19, 0.29, 0.58, and 0.48, respective ly, for conjunctival samples.