The RNA is capped and replication proceeds in the nucleus. The progeny are released by budding and cell death ensues. The segmented genome of the influenza virus allows rearrangements to occur in simultaneously infected cells. This accounts for the periodic appearance of new variants. The new variants are responsible for the process of antigenic shift.
Transmission of disease is airborne.
The viruses deposit in lower respiratory tract, their primary site is the tracheobronchial mucosa. Neuraminidase produces liquefaction, which leads to viral spread. Respiratory symptoms include a cough, sore throat and nasal discharge. There is no viremia but systemic symptoms such as fever and muscle aches do occur. The extent of respiratory tract cell destruction is a probable factor in the disease.