Department of Clinical Sciences, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran.
Avian Influenza (AI) is a viral respiratory disease of domestic and wild birds. In the diagnostic laboratory, it is essential to have methods for rapid detection of avian respiratory viruses. Cloacal swabs collected from chickens experimentally infected with H9 subtype AI virus, used in a reverse transcription-polymerase chain reaction (RT-PCR) assay for detection of AI. In infected animals, AI viruses are detected most frequently between days 3 and 7 post infection (p.i.). The RT-PCR assay was able to detect, at least, 103.5 EID50 of AI viruses in the allantoic fluid. The RT-PCR assay did not show any cross-reactivity with some other avian respiratory viruses. In comparison with virus isolation (VI) assay, the relative sensitivity, specificity, correlation rate and positive predictive value of the RT-PCR were 80%, 84%, 82% and 83%, respectively. The κ index of agreement between the two tests were substantial (κ = 0.64). The results proved that the RT-PCR assay could be a reliable and rapid alternative to VI assay for detection of AI viruses A H9 subtype H9 in fecal specimens.