Pathogenesis of influenza viruses
- virus first targets and kills mucus-secreting, ciliated, and other epithelial cells, causing the loss of this primary defense system.
- NA facilitates the development of the infection by cleaving sialic acid residues of the mucus, thereby providing access to tissue.
- If the virus spreads to the lower respiratory tract, the infection can cause severe desquamation (shedding) of bronchial or alveolar epithelium down to a single-cell basal layer or to the basement membrane.
- In addition to compromising the natural defenses of the respiratory tract, influenza infection promotes bacterial adhesion to the epithelial cells.
- Pneumonia may result from a viral pathogenesis or from a secondary bacterial infection.
- Influenza may also cause a transient or low-level viremia but rarely involves tissues other than the lung.
- -how does virus cause disease? It comes in through aerosol inoculation, entering & replicating in respiratory tract; in respiratory tract, it kills cells, so that there is temporary dysfunction; the immune response is stimulated to fight against viral infection- depending on how fast viral replication & immune response is, there may or may not be symptoms at this point; sometimes, the virus travels into the lower respiratory tract to cause pneumonia; when the virus is replicating and killing cells in the respiratory tract, you also make it more vulnerable to bacterial infection- dysfunction due to infection causes loss of ability to fight bacterial infection; in rare cases, viruses spread to blood, which spreads the virus to other organs (causing complications, ex. in brain)