IBDV antigen detection by immunohistochemical staining in virus-infected bursas. SPF chickens were inoculated with 104EID50 of cIBDV or vIBDV and bursal tissues were collected at PIDs 3, 5 and 7. Bursal sections from virus-free chickens, vIBDV- and cIBDV-infected chickens were examined for the presence of IBDV antigen by immunohistochemistry. IBDV positive cells were counted (40X) at PID 3, 5 and 7. The values represent the mean ± SEM of 5 fields/bursa/chicken on designated PID. *Statistically significant differences between vIBDV- and cIBDV-infected groups (p < 0.05).