Macroscopic and histopathological analysis of BF.

A) Representative images of the differences in the morphological aspect of BF collected 10 days post challenge in the different groups: (VP2-BP), vvIBDV challenged chickens immunized with the VP2 particles, showing normal appearance; (C+), vvIBDV challenged chickens immunized with the inactivated commercial vaccine, showing normal appearance; (Untreated), unchallenged naive chickens, showing normal appearance; (C-), vvIBDV challenged naive chickens, showing diffused hemorragic appearance. B) Histopathological pictures are representative of BF sections derived from 6 animals for each group and stained with hematoxylin and eosin. Diffuse necrosis of lymphocytes and marked atrophy of follicles are evident in the bursae of C- group. Loss of lymphocytes, within both medullary and cortex areas, results in multifocal, cystic cavities containing cellular debris (black arrows).