Neuraminidase-inhibition assay for the identification of influenza A virus neuraminidase virus subtype or neuraminidase antibody specificity.

The neuraminidase-inhibition (NI) assay is a laboratory procedure for the identification of the neuraminidase (NA) glycoprotein subtype in influenza viruses or the NA subtype specificity of antibodies to influenza virus. A serological procedure for subtyping the NA glycoprotein is critical for the identification and classification of avian influenza (AI) viruses. The macroprocedure was first described in 1961 by Aminoff and was later modified to a microtiter plate procedure (micro-NI) by Van Deusen et al. (Avian Dis 27:745-750, 1983). The micro-NI procedure reduces the quantity of reagents required, permits the antigenic classification of many isolates simultaneously, and eliminates spectrophotometric interpretation of results. Although, the macro-NI has been shown to be more sensitive than the micro-NI, the micro-NI test is very suitable for testing sera for the presence of NA antibodies and has proven to be a practical and rapid method for virus classification. This chapter provides an overview of the USDA validated micro-NI procedure for the identification of subtype-specific NA in AIV and antibodies.