Detection of influenza C virus by using an in situ esterase assay

Abstract

A variety of chemically defined compounds were tested to characterize the substrate specificity of the influenza C virus esterase and to determine whether a substrate could be found that would be useful in an assay to detect the virus. The new substrates, α-naphthyl acetate and α-naphthyl propionate, were identified; α-naphthyl acetate was employed to develop an assay specific for influenza type C virus in MDCK cells. The assay was sufficiently sensitive to detect esterase activity in a single cell and distinguished influenza C virus infections from those of types A and B viruses. Infected cells could be detected as early as 8 h postinfection, with maximal enzyme detection occurring at 24 h. Assay of influenza C virus in the chorioallontoic or amniotic fluid of infected eggs was performed by applying fluids directly onto nitrocellulose strips and then incubating with α-naphthyl acetate. Both the cellular and nitrocellulose-bound assays are rapid, inexpensive, and easy to perform, offering advantages for use in clinical laboratories.