Infectious bursal disease (IBD) is an acute, highly contagious, and immunosuppressive avian disease caused by IBD virus (IBDV). Differentiation of IBDV strains is crucial for effective vaccination programs and epidemiological investigations. In this study, a combination of clinical, histopathological examinations, immunohistochemistry and indirect immunofluorescence techniques were used to differentiate different IBDV strains. Sixty three weeks old chickens were divided randomly into five equal groups. Chickens of four groups were inoculated orally with different strains of IBDV. Chickens of the fifth group were kept as a control. Three chickens per group were euthanized at 3, 7, 14, 21 days post-inoculation (dpi). Euthanized chickens subjected to autopsy and tissue samples were collected in 10% neutral-buffered formalin for histopathology, immunohistochimestry and immunoflrourescence. The results revealed that clinical examination and histopathology cannot be used alone for differentiation of IBDV strains, while immunohistochemical and immunofluorescence techniques are reliable tools for differentiation of IBDV strains
