Acute viral nasopharyngitis pathophysiology

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

Rhinovirus (the most common cause of common cold) is usually transmitted via aerosols generated by coughing or sneezing. The entry point is usually the nose, however viruses can enter the body through the lacrimal ducts. Following transmission, the virus invades epithelial cells and causes a release of inflammatory cytokines, leading to the various symptoms of the common cold. The body responds using cellular and humoral immunity in addition to the role of bacterial flora in the defense against the organism.

Common colds are most often caused by one of more than 100 serotypes of rhinoviruses, a type of picornavirus. Other viruses that can cause colds are coronavirus, human parainfluenza viruses, human respiratory syncytial virus, adenoviruses, enteroviruses, and metapneumovirus.^[1][2][3]

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

1. Aerosols generated by coughing and sneezing
2. Saliva or nasal discharge, either directly or from contaminated surfaces

• Asymptomatic patients can transmit the infection, too.^[4]
• The infectious period (i.e. the 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 epithelium of the nasopharynx and rapidly multiplies.
• The virus enters the body mainly through the nose. Other entry points include the eyes through drainage of tears from the lacrimal ducts into the nasopharynx.

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• Viruses undergo frequent changes in their antigenic coat. This helps them evade the immune system and enables them to cause recurrent infections.
  • Rhinovirus binds to ICAM-1 receptors on epithelial cells and makes them release inflammatory cytokines, but does not cause damage to them.
  • Respiratory syncytial virus (RSV) 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.^[5]
  • Human parainfluenza virus causes inflammation of the respiratory tract, so parainfluenza infection is much more severe than other viruses.
• The body fights the offending viruses using both humoral immunity (i.e. IgA in the epithelium), and cell mediated immunity (i.e. different inflammatory cells in the adenoids and tonsils).^[3]
• Normal flora inhabitants in the nasopharynx also play an important role in eliminating the infection.

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