Table 1.

The scoring system showing the bursal injury after chickens were infection with IBDV.

Score	Bursal follicle	Fibro in bursa interstitium	Infiltrated inflammatory cells
0	No bursal damage in any follicle, clear demarcation of medulla and cortex	Size of bursal interstitium is normal	A few of inflammatory cells in bursa interstitium
1	<50% of follicles with severe lymphocyte depletion	Size of bursal interstitium become bigger, connective tissue emerge	Many inflammatory cells infiltrated in bursa interstitium
2	>50% of follicles with severe lymphocyte depletion	Connective tissue take up < 50% area of bursal interstitium	A large number of inflammatory cells infiltrated in bursa interstitium
3	Follicular outlines only remaining	Connective tissue take up > 50% area of bursal interstitium	A large number of inflammatory cells infiltrated both in bursa interstitium and follicle