Serological tests: As all influenza A viruses have antigenically similar nucleoprotein and matrix
antigens, these are preferred targets of influenza A group serological methods. Agar gel
immunodiffusion tests can be used to detect antibodies to these antigens. Concentrated virus
preparations containing either or both type of antigens are used in such tests. Not all species of
birds develop demonstrable precipitating antibodies. Enzyme-linked immunosorbent assays have
been used to detect antibodies to influenza A type-specific antigens in either species-dependent
(indirect) or species-independent (competitive) test formats. Haemagglutination inhibition tests have
also been employed in routine diagnostic serology, but it is possible that this technique may miss
some particular infections because the haemagglutinin is subtype specific.