Studies on infectious bursal disease in chickens. 2. Scoring microscopic lesions in the bursa of fabricius, thymus, spleen, and kidney in gnotobiotic and battery reared White Leghorns experimentally infected with infectious bursal disease virus.

During a 2 1/2 year study on the effect of experimentally-induced infectious bursal disease (IBD) in White Leghorns, a system for scoring microscopic lesions was developed. Microscopic changes in the bursa of Fabricius, thymus, spleen, and kidney were studied to create a lesion score for each organ. No changes occurred in the cecal tonsil and few, if any, changes occurred in the liver. The system was useful in evaluating the severity of pathologic and inflammatory changes in each organ during the course of the disease. Lesion scores for the bursa ranged from 0 for normal bursae to +4 for severely affected bursae. The lesion scores for the thymus, spleen, and kidney ranged from 0 to +3. The criteria for scoring lesions in the thymus were: 0 equaled no change; +1- cortex had a few empty spaces, pronounced hyperemia with some heterophil infiltration, especially in the medulla; +2- cortex had an increase in the number of empty spaces and increased heterophil infiltration, and the cortex and medulla had decreased hyperemia; +3- cortex had numerous round aggregations (12 to 16 mu in diameter) of cell debris and pyknotic nuclei, a definite decrease in the lymphocyte density in the cortex, and decreased hyperemia in cortex and medulla. This lesion scoring system was useful in determining the severity of IBD in different-aged progeny from IBD-immune and nonimmune dams.