Morphological evidence of apoptosis in chickens infected with infectious bursal disease virus.

Two-week-old specific pathogen-free chickens were infected with the infectious bursal disease virus by the ocular route. Immediately, and at 4 and 8 days after infection, groups of three chickens were killed and tissue samples were collected. Under electron microscopical examination, typical apoptotic cells were seen in the bursa of Fabricius (BF) and in the spleen. Tissue sections stained with haematoxylin and eosin were subjected to image analysis to quantify cellular depletion in the follicles of the BF. Unstained sections were treated with a terminal deoxy-transferase-based kit to detect apoptotic cells. The numbers of apoptotic cells at different stages of infection were counted by image analysis. The results revealed a rapid depletion of cells in the BF and a simultaneous increase in apoptotic cells.