Characterization of Infectious Bursal Disease

Natural outbreaks and experimental infections of I.B.D. (infectious bursal disease) in chickens were investigated. In field studies, a consistent additional sign of I.B.D. in affected flocks was slight head and body tremors 1 to 2 days before outbreaks were clearly evident. Body temperatures were above normal (0.56 ° to 1.67°) early in the disease but dropped markedly (below 35 ° C.) before death. Gross pathological changes of some sort occurred in the bursa in 100 % of the cases. Birds that died usually had atrophied bursas (84%), hemorrhages in skeletal muscles (80%), excessive urates in the kidneys (84%) and atrophied spleens (76%). Mortality usually peaked at 4-6 days after onset of the disease. In experimentally-infected chickens, clinical signs of I.B.D. were evident by 24-48 hours. Chickens passed thick yellowish mucoid droppings by 48 hours and peak depression oc-curred by 3-4 days. Birds usually recovered by 6-10 days. Some gross pathological changes in bursas occurred by 36 hours. Bursas had begun to hypertrophy and some were surrounded by a yellowish jelly-like film with maximum hypertrophy by 48 hours. They were markedly atrophied by 120 hours and thereafter. Liver and spleen were significantly hypertrophied