Comparison of the Infectivity in Filamentous and Spherical Influenza Virus

Abstract

In addition to spherical influenza virus, filamentous virus particles have been noted in every main strains of influenza virus examined, especially in recently isolated strains. Although the filamentous influenza virion has been found to possess many of the biological properties of spherical influenza virus, the question of the infectivity of filaments relative to that of spheres remains in doubt. Two influenza A virus, A/WSN/33 and NWS-F, representing spherical and filamentous morphology, respectively, were supplied by professor E.D. Kilbourne. A/WSN/33 and NWS-F came from same parent strain but NWS-F containing the M gene and NA gene of RI/5+, which has high proportion of filamentous particles. The morphology of the viruses were revealed under the electron microscope. The infectivity were estimated by plaque assay and the quantity of virus particle was determined by hemagglutination assay. To avoid prejudice, the identities of the viruses have been kept blind to researchers until the morphological feature and infectivity of the viruses had been determined. The results indicated that the influenza filaments have higher infectivity in MDCK cells than that of the spheres. Although the presence of filaments has not yet been demonstrated in the nasal washing from infected human, it may be of practical importance in the monitoring of influenza epidemics.