A variety of wild waterfowl appear to be the predominant natural reservoir for Influenza A viruses and subtypes representing most of the hemagglutinin and neuraminidase combinations can be found circulating in these birds. Historically, human influenza virus infections have been associated with H1N1, H2N2, and H3N2 subtypes of influenza A, although a recent (1997) and significant outbreak in Hong Kong was identified as an H5N1 subtype. This outbreak was not only significant because it resulted in 18 human infections and 6 deaths, but it also represented the first known demonstration of avian influenza virus transmission to humans.

Depending upon the serological requirements or research interest (natural infection, vaccine monitoring, or DIVA [Differentiation of Infected from Vaccinated Animals]), it may be useful to monitor the development of influenza A NP-specific antibody in a variety of species. ImmTech has developed a highly sensitive and specific enzyme-linked immunosorbent assay (ELISA) for the detection of influenza A NP-specific antibodies in serum from human and veterinary sources. Because the assay utilizes "inhibition of binding" technology, it may be used with serum from any species, and therefore does not require species-specific conjugates. The assay can be completed in less than 1.5 hr., contains only one wash step, and incorporates proprietary diluents that are designed to prevent the development of nonspecific signal derived from sample matrix and/or the nonspecific adsorption of reactive test components. The result is an assay that is both highly sensitive and specific.