The PNDV-borne periods of the brains and the spleens of the ducklings inoculated by intramuscul ar injection or nose/eye dropping are not more than 14 days.

• 而经肌肉注射或滴鼻点眼途径均未能使北京雏鸭发病，且其脑和脾脏的带毒时间不超过14天。