Respiratory disease and immunity to challenge produced by Australian strains of infectious bronchitis virus

Six Australian isolates of IB virus were compared as to the severity of respiratory disease they produced and the immunity to challenge they conferred to the respiratory system. Only one isolate. Vac G/15, produced significant disease. Four viruses fully protected the respiratory system from challenge (Vac A(3), Vac 3, 2032, and Vac 4) while two viruses partially protected this system (Vac 3/10 and Vac G/15). A comparison between tracheal organ culture, histopathology and virus isolation as a means of measuring respiratory disease gave a high correlation between the methods.