Rapid differentiation of current infectious bronchitis virus vaccine strains and field isolates in Australia

Abstract

Rapid differentiation of vaccine strains of infectious bronchitis virus (IBV) from wild type strains would enhance investigations of disease outbreaks. This study aimed to develop a reverse transcription-polymerase chain reaction (RT-PCR) assay to differentiate between Australian vaccine strains of IBV and field isolates. A fragment of 6.5 kilobases that contains the S, M and N genes was amplified by RT-PCR from ten different IBV strains, including vaccine strains and field isolates, and then sequenced. Comparison of the sequences of these strains revealed a deletion of 58 bases in the 3' untranslated region (UTR) of IBV vaccine strains but not in the field isolates. Two primers were designed to amplify a fragment of the 3' UTR that differed in size between the vaccine strains and field isolates. RT-PCR was performed using these two primers to screen 20 IBV strains, including field isolates and the vaccine strains. All strains were correctly identified as either vaccine strains or field isolates. This procedure is a rapid, sensitive and inexpensive method for discrimination between most current Australian vaccine strains and field isolates of IBV.