Table 2. Evaluation of pathogenicity according to virus dose in SPF chickens

Group	Age (d)	Virus titer (TCID50/dose)	Mortality	Gross lesions		Histological lesion score		Virus detection rate		Mean bodyweight gain (g) at days post inoculation (DPI)
				HN	HP	Liver	Heart	Liver	CT	3	5	10
YS4 100	14	6.31 × 108	1/91)	5/9	0/9	2.11 ± 0.78	0.55 ± 0.72	7/9	9/9	7.4	−7.0	40.2
YS4 10−1	14	6.31 × 107	0/9	3/9	0/9	1.66 ± 0.86	0.33 ± 0.71	7/9	9/9	13.8	15.6	61.2
YS4 10−2	14	4.73 × 106	0/9	3/9	0/9	1.44 ± 0.88	0.33 ± 0.71	6/9	9/9	25.1	16.3	69.5
Control	14	–	0/9	0/9	0/9	0.0 ± 0.00	0.00 ± 0.00	0/9	0/9	36.4	30.2	75.3

Positive chicken number / tested chicken number.
YS4 10⁰, No diluted virus passaged 4 times in yolk sac of SPF chicken embryonated eggs.
YS4 10⁻¹, Ten-fold diluted virus passage 4 times in yolk sac of SPF chicken embryonated eggs.
YS4 10⁻², One-hundred fold diluted virus passaged 4 times in yolk sac route of SPF chicken embryonated eggs.
SPF, specific-pathogen-free; HN, hepatic necrosis; HP, hydrppericardium; CT, cecal tonsil.