Acute viral nasopharyngitis pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1];Associate Editor(s)-in-Chief: Ahmed Younes M.B.B.CH [2]

Pathophysiology

Virus

Common colds are most often caused by infection by one of the more than 100 serotypes of rhinovirus, a type of picornavirus. Other viruses causing colds are coronavirus, human parainfluenza viruses, human respiratory syncytial virus, adenoviruses, enteroviruses, or metapneumovirus.

Transmission

Cold viruses are spread by aerosols created when a patient sneezes

The common cold virus is transmitted between people by one of two ways:

• In aerosol form generated by coughing, sneezing, or
• From contact with the saliva or nasal secretions of an infected person, either directly or from contaminated surfaces.

• Symptoms are not necessary for viral shedding or transmission, as a percentage of asymptomatic subjects exhibit viruses in nasal swabs.
• The infectious period (time during which an infected person can infect others) begins about one day before symptoms begin, and continues for the first five days of the illness.
• The virus enters the cells of the lining of the nasopharynx (the area between the nose and throat) and rapidly multiplies.
• The major entry point is normally the nose, but can also be the eyes (in this case drainage into the nasopharynx would occur through the Nasolacrimal duct).

Pathogenesis

• Viruses undergo frequent changes in their antigenic coat. This helps the viruses to evade the immune system and enables them to cause recurrent infections.
• Rhinovirus binds to ICAM-1 receptors on epithelial cells. Binding to ICAM-1 receptors releases inflammatory cytokines but does not cause damage to epithelial cells.
• Respiratory syncytial virus does not cause any release of cytokines. Instead, it replicates in the nose and pharynx. In many occasions, it can spread to the lower respiratory tract.
• Human parainfluenza virus causes inflammation of the tract and subsequently, parainfluenza infection is much more severe than other viruses.
• The body responds using both humoral immunity (IgA in the epithelium) and cellular immunity (different inflammatory cells in the adenoids and tonsils) to fight the offending virus.
• Normal flora inhabitants in the nasopharynx also play an important role in eliminating the infection.