Characterization of H9N2 avian influenza virus isolated from a chicken co-infected with H5N1 virus.

Abstract

Avian influenza caused by avian influenza viruses (AIV) has become a serious threat to poultry industry worldwide due to the huge economic loss and incidence of human infections in many countries around the world. India has been experiencing intermittent outbreaks of both H9N2 and H5N1 since 2003 and 2006, respectively. Retrospective testing of samples collected from West Bengal during outbreak of H5N1 virus in 2008 revealed mixed infection of both viruses within the same host. In this study, we report the molecular and pathogenic characterization of an H9N2 AIV isolated from a chicken co-infected with H5N1 virus. The sequencing of all the eight genes of the H9N2 virus was carried out. Phylogenetic analysis of HA gene of the H9N2 virus indicated grouping with G1 lineage viruses. The PA, NS, Matrix, PB1, PB2 and NP genes were closely related to H7N3 isolate from Karachi and the NS and polymerase genes did not group with any known lineage of H9N2 viruses. This confirmed that the H9N2 virus was a reassortant between G1and an unknown lineage. The absence of multiple basic amino acids in H9N2 virus (RSSR*GLF) indicated low pathogenicity of the virus in chickens. Molecular analysis revealed the presence of unique amino acids and susceptibility to oseltamivir and amantadine group of antivirals. The intra venous pathogenicity index of the H9N2 virus was found to be 0.325 H9N2. The result indicated that the H9N2 virus is low pathogenic to poultry. These findings corroborate the need for continued surveillance of Indian poultry to monitor the reassortant and evolutionarily divergent avian influenza viruses which might cause huge loss to the Indian poultry industry.