Infectious bursal disease is a contagious viral disease of Fabricius' bursitis in chickens aged 3-6 weeks. It is a very serious economic disease. It is caused by an immunosuppressive birnavirus.
The first symptom in sick chickens is mucoid or watery, whitish diarrhoea. The chickens cling to each other's cloacae, refuse water and feed, huddle under heat sources, refuse to move and die of exhaustion.
The pathology is acute bursitis. The bursa is hyperemic, oedematous with longitudinal annealing on the surface, followed by necrotic debris and occasionally persistent haemorrhages. Changes in other organs are secondary and not regular. Haemorrhages of varying size and severity may occur in the subcutaneous tissue, skeletal muscles of the legs, chest and wings, or as a result of dehydration.
