Rapid detection and identification of avian infectious bronchitis virus

A rapid and sensitive method for the detection and unambiguous typing of infectious bronchitis virus (IBV) is described. RNA was isolated from IBV-infected allantoic fluid and was transcribed into cDNA. This cDNA was amplified by the polymerase chain reaction. The polymerase chain reaction products were subsequently analyzed on an agarose gel. The presence of IBV-specific RNA in the allantoic fluid then allowed the amplification of a 438-bp DNA fragment from the nucleocapsid (N) gene. For the typing of IBV isolates, we used amplified double-stranded DNA as a template in a sequencing reaction. We report 360 bases of the N gene of 18 IBV isolates. The sequence of the N gene was different between serologically indistinguishable IBV strains and may be a valuable tool in epidemiologic studies. A phylogenetic tree that was based on the sequences obtained did not agree with trees that were based on other parts of the sequence, illustrating the high frequency of recombination between IBV strains.