Isolation and Identification of Avian Influenza Virus H9N2 Subtype

In August 1998, the avian influenza (AI) outbreak appeared in one of the layer farros in Tehran province. Birds on the affected farro exhibited respiratory infection and reduction of egg production with very low mortality. An agar gel precipitation (AGP) test using AIV antiserurn revealed the presence of the virus in the sarnples from the affected birds. The sera collected from the surviving birds of the afTected flocks also showed the presence of antibodies against AIV by AGP test. An avian influenza virus H9N2 subtype was isolated in embryonated eggs from the tracheal and clocal swabs as weil as pooled visceral organs of the afTected birds and coded AlchickenlIran/259/19981H9N2. Virulence testing of the low passage virus was undertaken at the time of the outbreak in specific pathogen free (SPF) chickens. The experimentally infected chickens showed significant clinical signs and recovered gradually without any death. The isolated virus was characterized as nHP AI on the basis of pathotyping studies in SPF chickens. It is the first report on isolation of AIV from the chicken flocks in Iran.