RNA associated with a nucleoprotein within a capsid comprised of matrix protein. The envelope bears club-shaped glycoprotein projections. The virus enters the host cell, and the uncoated genome is transcribed and translated.
New virions form by budding from host cell membranes.
Pathogenesis Transmission is usually via airborne droplets to the nasal mucosa. Virus replicates locally in cells of the ciliated epithelium, causing cell damage and inflammation. The appearance of antibody in serum and nasal secretions is followed by resolution of the infection. Immunity wanes within a year or two. Epidemiology Incidence peaks in the winter, taking the form of local epidemics lasting a few weeks or months.