Pathological investigation and immunohistochemical evaluation of bursa of Fabricius in naturally infected chicken with infectious bursal disease

The present study was conducted to investigate the pathology and immunohistochemical expression of CD4+ and CD8+ T cells in Infectious bursal disease (IBD) affected chicken from14 poultry flocks (February, 2017 to July, 2018). The flocks belonged to different regions of Haryana having the history of IBD vaccination with Georgia and intermediate plus vaccines at 12–15 days. Chicken had sudden death with clinical symptoms like diarrhoea from 3 to 4 days. Carcasses were moderately dehydrated. Macroscopically, petechial and ecchymotic haemorrhages were observed in pectoral, thigh and leg muscles. Bursa of Fabricius (BF) revealed oedema, fibrinous exudates and severe haemorrhages. Congestion was evident in thymus, spleen, caecal tonsils, kidneys and intestine. Microscopically, BF showed severe congestion, haemorrhages, marked depletion and necrosis of lymphocytes, fibrous connective tissue proliferation along with heterophilic infiltration. Thymus, spleen and caecal tonsils revealed marked haemorrhages, depletion and necrosis of lymphocytes. Congestion was observed in lungs, heart and intestines. Immunohistochemical studies showed increased widely scattered CD4+T cells in follicles below the plical lining epithelium, inter-follicular and cortico-medullary portion. Numerous immunopositive increased CD8+ T cells were present throughout the bursal follicles. The increased CD4+ and CD8+ T cells in the bursal follicles indicate the possibility of the role of these cells in the clearance of viral infection.