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

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Abstract
A sensitive assay was developed for the measurement of neuraminidase with use of the 4-methylumbelliferyl-α-ketoside of N-acetyl-neuraminic acid as a fluorescent substrate. Neuraminidase activity was detected in preparations containing small quantities of cultivated influenza virus as well as in some nasal wash specimens from human volunteers experimentally infected with influenza AIAlaska/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.