Systematic Veterinary Virology

LESIONS

• The following lesions are observed in dead birds
• Enlareged cloacal bursa which is swollen and haemorrhagic in birds dead of the disease and is atrophied in recovered birds
• Dehydrated carcass
• Dark skeletal muscles with haemorrhages (especially thigh and pectoral muscles)
• Opaque thymus with thickened gelatinous capsule 
• Fatty and yellow or pink bone marrow
• Swollen liver
• Swollen kidneys
• Intestines with increased mucus
• Changes in bursa:
• Within three to four days post infection there is an inflammatory hypertrophy of the bursa and apoptosis of B-lymphocytes.
• Within two days of infection there is complete depletion of cells in the follicular cortex and after a week the follicular structure may not be visible at all. At four to six days post infection the bursa is swollen, hemorrhagic and covered by a gelatinous exudate.
• The bursa will reach five times its normal size during acute infection before atrophy begins. Ten days post infection the bursa will be one eighth of its original size and after two months a repopulation of the bursa occurs.
• At necropsy an atrophied, grey bursa is seen with no Blymphocytes in the bursal follicles or in other lymphoid tissues. (Recently it has been shown that T-cells also are affected by IBDV infection. This might be explained by a macrophage-mediated inhibition of the T-cells ability to respond to mitogenic stimulation or an activation of T-suppressor cells)