Fluorometric Assay for Measurement of Viral Neuraminidase--Application to the Rapid Detection of Influenza Virus in Nasal Wash Specimens

A sensitive assay was developed for the measurement of neuraminidase with use of the 4-methylumbelliferkyl-alph-ketoside of N-acetyl-neuraminic acid as a fluorescent substrate. Neuraminidase activity was detected in preparation containing small quantities of cultivated influenza virus as well as in some nasal wash specimens from human volunteers experimentally infected with influenza A/Alaska/78 virus. Activity due to influenza viral neuraminidase could be distinguished from activity due to bacterial or mammalian (fibroblast) neuraminidase by means of enzyme inhibition with ethylenediaminetetraacetate, a chelating agent. The same substrate could be used in a solid-phase assay to determine the antigenic type of the influenza viral neuraminidase. The fluorescent neuraminidase assay takes 2-4 hr to perform and uses equipment available in many laboratories. Thus, it offers promise for the rapid detection of influenza viruses in cell cultures and clinical specimens.