Neuraminidase-Inhibition Assay for the Identification of Influenza A Virus Neuraminidase 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 macro-procedure was first described in 1961 by D. Aminoff et al. [2 ] and was later modified to a microtiter plate procedure (micro-NI) by Van Deusen et al. [4 ]. The micro-NI procedure reduces the quantity of reagents required, permits the antigenic classification of many isolates simultaneously, and eliminates the 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 will provide an overview of the USDA-validated micro-NI procedure for the identification of subtype-specific NA in AIV and antibodies.