Respiratory tract is one of portal of entry for infectious agent enters the susceptible host. Other portal of entries are GI tract, genitourinary tract or skin or mucous membranes.
Influenza viruses have a high affinity for epithelial cells of the respiratory tract mucosa.
The infection causes necrosis and shedding of the serous and ciliated cells lining the respiratory tract, allowing extracellular fluid to leak out and produce the nasal discharge. Upper respiratory tract illness caused by influenza is characterized by a dry hacking cough that peaks after 3 to 4 days and persists for more than 1 week after other symptoms resolve.
Complications involving the upper and lower respiratory tract of influenza include acute otitis media, sinusitis, bronchitis, croup and pneumonia.
Upper respiratory tract (mouth and nose) also may serve as portal of exit, from which secretions carrying the virus are excreted through coughing and sneezing.
Respiratory tract flu infection
