Table 1. Clinical characteristics of mice.

Virus	Death	Impending death	Clinical symptoms of alive	Pathological change of lung tissues
WT	0	0	None	None
MA-1	0	0	None	None
MA-2	0	0	2/3 hunched posture and ruffled fur	None
MA-3	0	0	3/3 hunched posture and ruffled fur	1/3 appeared nidus near hilum of lung
MA-4	0	0	3/3 hunched posture, ruffled fur	3/3 large area of lungs appeared lesions
MA-5	0	0	3/3 hunched posture, ruffled fur	3/3 large area of lungs appeared lesions
MA-6	1	0	2/2 hunched posture, ruffled fur	2/2 large area of lungs appeared lesions
MA-7	1	1	2/2 hunched posture, ruffled fur	2/2 all area of lungs appeared lesions
MA-8	2	1	1/1 hunched posture, ruffled fur	1/1 all area of lung appeared lesions

Note: WT, wild-type; MA, mouse-adapted and the number represents the passage. Groups of mice (n = 3 per group) were inoculated with each type of wild-type or mouse-adapted virus and monitored for three days. Subsequently, the mouse lungs were collected and the supernatants of lung homogenates were used for serial passages.