Isolation and characterization of low pathogenic H9N2 avian influenza A viruses from a healthy flock and its comparison to other H9N2 isolates.

Several outbreaks of avian influenza (AI) caused by H9N2 subtype, have been reported in the poultry industry during 1990 around the globe. Currently, H9N2 are endemic in the large area of Middle and Far East, including Pakistan. Since H9N2 AI viruses are sporadically reported from humans, extensive incidence of H9N2 in poultry imposes a great risk for human health. In this context, continuous monitoring of the poultry and determining the genetic nature of these viruses are fundamental to predict any future threat. Thus gene sequences of one isolate of H9N2, isolated from commercial poultry flocks, were analyzed. The results of this investigation, based on hemagglutinin (HA), neuraminidase (NA) and non-structural genes, showed that Pakistani H9N2 isolates are closely related to each other and to other H9N2 isolates from the Middle East. However, several unusual substitutions with unknown functional consequences were observed in HA and NA proteins and thus warrant further investigations for their possible role in viral biology. In conclusion, these findings provide information regarding the genetic nature of H9N2 avian influenza viruses in Pakistani poultry and necessitate the sequencing of more H9N2 viruses from both naturally infected and vaccinated flocks.