Immunohistochemical detection of swine influenza A virus in formalin-fixed and paraffin-embedded tissues

An avidin-biotin complex (ABC) immunohistochemical method utilizing a commercially-available polyclonal antiserum to human influenza A virus was used to detect antigens of influenza A virus in formalin-fixed, paraffin-embedded tissues of swine. Influenza A antigens were immunohistochemically detected in 28/30 cases in which influenza A virus was demonstrated by virus isolation and in 5/22 cases suspected to be influenza A-infected by clinical and histological criteria, but from which the virus was not isolated. Viral antigen was not demonstrated in 30/30 cases not suspected clinically or histologically to be associated with influenza infection. This method is a convenient, sensitive, and specific means of influenza A virus detection and is applicable to both routine diagnosis of influenza A virus infection and to retrospective and prospective studies of the occurrence and the pathogenesis of this virus in pigs.