Experimental Production of Complicated Chronic Respiratory Disease Infection ("Air Sac" Disease)

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Abstract
Six experiments were conducted to determine the role of pathogenic pleuropneumonia-like organisms (S6 PPLO), infectious bronchitis virus (IBV), and pathogenic Escherichia coli, singly and in combination in the production of complicated chronic respiratory disease. Results were best when the first two agents were injected into the posterior thoracic air sac of PPLO-free chickens and the E. coli was inoculated intratracheally. Control chickens were exposed to the inoculated birds by contact in the same pens. The results were evaluated in terms of mortality and severity and nature of the lesions. Lesions were produced that were indistinguishable from the typical field disease[long dash]a fibrinous or fibrino-purulent pericarditis and peri-hepatitis, air sacculitis, and some cases of salpingitis. The experimentally produced disease, in descending order of severity, was produced by the following infective agents or combinations of agents: 1) E. coli + PPLO + IBV; 2) E. coli + PPLO; 3) E. coli + IBV; 4) E. coli alone. The same general relationship was noted in the severity of the disease transmitted to the control birds by contact.