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 evalua ted using the IBV and Escherichia coli mixed-infection model. Based on the clinical signs, mortality, and lesions, the isolates were classif ied as high, intermediate, and low in pathogenicity. The in vivo class ification was compared with the serotype classification results obtain ed by reverse transcriptase-polymerase chain reaction-restriction frag ment length polymorphism analysis. The high-pathogenicity group was co mposed of five isolates representing three serotypes: Arkansas, Georgi a variant (GAV), and Massachusetts. Isolates in the intermediate- and low-pathogenicity groups were all representatives of the Connecticut s erotype, except for one isolate, which belonged to the Massachusetts s erotype.