Influenza A viral nucleoprotein detection in isolates from human and various animal species.

A double antibody sandwich, enzyme-linked immunosorbent assay (DAS-ELISA) was developed to detect influenza A viral antigen, employing a monoclonal antibody directed against type-specific influenza A nucleoprotein (McAb anti-NP). McAb anti-NP was used to coat ELISA plates as well as to prepare the peroxidase conjugate. Influenza A viruses of avian, equine, swine, and human origin were detected in allantoic fluids of inoculated eggs with higher sensitivity by the DAS-ELISA than by hemagglutination (HA) assays. Minimal concentrations of 8 ng/ml influenza virus protein were detected in Nonidet P40-treated virus preparations. Viral antigen detection in tissues of experimentally infected chickens and pigs was successful, but in pigs yielded a lower positive score than the conventional method of virus isolation in eggs. The test is sensitive, rapid, and easy to perform, but does not permit influenza A subtyping. In avian species, the McAb anti-NP DAS-ELISA differentiates between influenza and Newcastle disease viruses. In pigs, the test distinguishes between influenza and Aujeszky's disease.