Serologic and genetic characterization analyses of a highly pathogenic influenza virus (H5N1) isolated from an infected man in Shenzhen

Highly pathogenic avian influenza (HPAI) H5N1 virus caused a wave of outbreaks in China during 2005--2006, resulting in a total of 20 cases of human infection in 14 provinces of China. On June16, 2006, a case of H5N1 human infection was confirmed in Shenzhen. The virus isolated from the patient, A/Guangdong/2/06, was characterized genetically and the relationship between the tracheal virus load and the antibody titer of the infected man was analyzed. Serological analysis confirmed that the patient's neutralizating antibodies had been generated 2 weeks after the onset of symptoms. The patient's serum antibodies could efficiently neutralize A/Guandong/2/06 infectivity in vitro. Phylogenetic analysis showed that the H5N1 virus of Shenzhen belonged to subclade 2.3.4, which contained viruses that were mainly responsible for the outbreaks in domestic poultry and in the cases of human infection in southern China. Homology and molecular characterization analysis revealed that all the segments of Shenzhen H5N1 virus still belonged to avian segments. Several specific amino acid residue mutations were detected.