Differentiation and Detection of Infectious Bronchitis Virus Subtypes by Immunofluorescence

A wide range of cross-reactions among strains was found when immunofluorescence was used as a method for differentiation of IBV strains. Only conjugates prepared against 97 and Massachusetts strains were able to detect all the strains of IBV included in this study. The fluorescence with heterologous strains was weaker than the one present when tested with homologous strains. When the rinsing period after staining was extended from 10 minutes to 2 hours, the cross-reactions were markedly diminished, and only 97 and Holte conjugates gave bright fluorescence with other than their homologous strains. Holte conjugate gave good fluorescence with virus 97, and the 97 and 609 conjugates with Gray virus. Thus, the fluorescent antibodies appear to offer possibilities for the differentiation of IBV isolates. When infected hens were examined, IBV antigen was detected by fluorescent antibodies only in the larynx, trachea, and lung. The conjugates contained antibodies against Marek's Disease agent. In addition they produced some fluorescence which behaved in the bird tissues as a specific reaction but was eliminated by absorption with chicken or rabbit liver tissue powder. Therefore, when diagnosing IBV or any other disease in chicken tissue one should be aware of the possibility of extraneous antibodies or antigens even in chickens which appear healthy and are from a specific pathogenfree flock.