To determine the etiologic agents of two atypical pneumonia human cases in Hunan Province in 2005-2006 and to study their pathogenic potential,the patients´ respiratory tract samples and sera were collected.The respiratory tract samples were tested by real-time RT-PCR and RT-PCR methods,and the sera by hemagglutination-inhibition assay.Virus was isolated from case 2 and its genome was sequenced and analyzed.Results showed the H5 nucleic acid tests of two cases were positive.The H5-specific antibody titer of...