Characterization of a highly pathogenic avian influenza H5N1 clade 2.3.4 virus isolated from a tree sparrow

The spread of H5N1 virus into a wide range of avian and mammalian species may facilitate the adaptation of the virus to human populations. In the present study, a survey of avian influenza virus in tree sparrows was performed and a HPAI H5N1 virus (A/tree sparrow/Jiangsu/1/08) was isolated. The H5N1 virus was found to be a genotype V variant belonging to clade 2.3.4, which had newly emerged in southern China in 2005. Genetic analysis showed that it had a close relation with A/Jiangsu/1/07 (H5N1), which was thought to be responsible for a probable limited person-to-person transmission in a family cluster in China in 2007. Pathogencity studies showed that the virus was highly virulent when experimentally inoculated into the chickens, tree sparrow, and mouse. As clade 2.3.4, genotype V variant of H5N1 virus has been accounted for the most of human fatal cases in China during 2005–2008, the existence of such H5N1 variants in the tree sparrows highlights the potential threat of this type of wild bird infection to veterinary and public health.