Detection of antibodies to the nonstructural protein (NS1) of avian influenza viruses aflows distinction between vaccinated and infected chickens

To differentiate avian influenza virus (AIV)-infected chickens vs. chickens immunized with inactivated avian influenza virus, an enzyme-linked immunosorbent assay (ELISA) was developed using a recombinant nonstructural protein (NS1) as the diagnostic antigen, which was cloned from an AIV H9N2 subtype strain isolated during the avian influenza outbreak of 2003-04 and expressed in Escherichia coli. Antibodies to the AIV NSI protein was only detected in the sera of chickens experimentally infected with AIV but not in the sera of chickens immunized with inactivated vaccine. This ELISA is useful for serological diagnosis to distinguish chickens infected with influenza viruses from those immunized with inactivated vaccine.