Rapid serotyping of infectious bronchitis virus isolates with the hemagglutination-inhibition test

The hemagglutination-inhibition (HI) test was evaluated as a method of typing recent suspect infectious bronchitis virus (IBV) isolates. Hemagglutination (HA) antigen was prepared from each isolate by phospholipase C treatment of virus concentrated from allanto-amniotic fluids of infected chicken embryos. An HI test was run with the HA antigen of each isolate against a battery of 17 antisera that had been prepared against different IBV strains classified by virus neutralization (VN). The HI test identified Ark 99 and Holland isolates that were similar to strains previously classified by VN. Two isolates included in this study were not inhibited by any of the reference antisera and therefore appeared to be antigenically different. The isolates were also evaluated by VN, and the results of the VN and HI methods agreed. Therefore the results suggest that the HI test can be useful for making a rapid, presumptive identification of new IBV isolates.