Abstract:To understand the mechanisms of H5N1 pathogenicity, we infected 6 to 8-week-old BALB/c mice by different routes of viral inoculation. The virus caused severe disease in mice, characterized by induced hypothermia, rapid weight loss, and high mortality by 2 days postinfection. And the main clinical signs of the animals began to recover by 4 days postinfection. The most severe and widespread lesions were observed in the organs of virus-infected mice, where received the virus firstly. Only mild lesions or no lesions were observed in spleens and brains. The principal lesions were occured in 2 days postinfection. Except kidney and heart, the lesions were recovered after 4 days postinfection.