Detection and differentiation of avian infectious bronchitis viruses using a monoclonal antibody-based

A sandwich ELISA (sELISA) employing four monoclonal antibodies as capture and IgG from egg yolk of hyperimmune hens as detecting antibodies was developed for the simultaneous detection and differentiation of infectious bronchitis virus (IBV) antigen in both allantoic fluid and tissues from experimental and field infections. Between 10(2) and 10(3) median ciliostatic dose (CD50) of virus was required for the detection of the majority of IBV strains in allantoic fluid. In chicks infected with 10(4 )to 10(6) CD50 of virus there was a good agreement between sEOSA and virus isolation. EBV antigen was detected in trachea of chicks having virus titres of 10(2 )CD(50). Following vaccination with the recommended dose of two IB vaccines, IBV antigen was not detected by sELISA. There was also a good correlation between sELISA and virus isolation on samples obtained from field infections. In two broiler flocks with respiratory disease, IBV antigen was detected by sELISA in a high proportion of samples. In one flock, two antigenically different strains were detected, one of which was vaccine virus. The other IBV strain identified was a new antigenic variant not previously detected.