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Avian Influenza A virus (AIV), a member of the Orthomyxo-viridae family, is a negative-sense, single-strand RNA virus, and is classified into subtypes based on 2 main surface gly-coproteins, hemagglutinin (HA) and neuraminidase (NA). To date, 16 HA subtypes (H1–H16) and 9 NA subtypes (N1–N9) have been identified. HA is the most important antigenic determinant to which neutralizing antibodies are directed.5,10 HA is cleaved into 2 fragments after maturation, hemagglutinin 1 (HA1) and hemagglutinin 2 (HA2), of which HA1 is the main domain of HA to induce antibodies. Chickens immunized with whole HA or HA1 subunit vac-cines produce strong humoral immune responses with high titers of HA-specific antibodies.12 Although both antigen and antibody detection techniques can be used to detect AIV infection, antigen detection is pre