In vivo evaluation of the pathogenicity of field isolates of infectious bronchitis virus.

The pathogenicity of 13 field isolates of infectious bronchitis virus (IBV) isolated from Georgia broiler farms from 1989 to 1992 was evaluated using the IBV and Escherichia coli mixed-infection model. Based on the clinical signs, mortality, and lesions, the isolates were classified as high, intermediate, and low in pathogenicity. The in vivo classification was compared with the serotype classification results obtained by reverse transcriptase-polymerase chain reaction-restriction fragment length polymorphism analysis. The high-pathogenicity group was composed of five isolates representing three serotypes: Arkansas, Georgia variant (GAV), and Massachusetts. Isolates in the intermediate- and low-pathogenicity groups were all representatives of the Connecticut serotype, except for one isolate, which belonged to the Massachusetts serotype.