The Common Cold: Causes and Pathogenesis

The Common Cold

• The common cold is a respiratory illness with symptoms like nasal stuffiness, sneezing, headache, rhinorrhea, general malaise, lacrimation, sore throat, and low-grade fever.
• The most common causes are Rhinovirus and Human Coronavirus.
• Other viruses associated with cold-like symptoms include influenza, parainfluenza virus, respiratory syncytial virus (RSV), adenovirus, coxsackie virus, human metapneumovirus, and bocavirus.

Pathogenesis of the Common Cold

• Viruses enter the body through inhalation.
• They infect cells lining the nasal passages and pharynx, attaching to viral receptors like ICAM-1, aminopeptidase N (APN), and sialic acid.
• Influenza is known to damage nasal epithelium by destroying ciliated columnar epithelial cells.
• Rhinovirus infections do not cause destruction of the nasal epithelium but rather induce inflammatory changes with hyperemia, edema, and leukocyte inflammation.
• Cytokines like IL-1β, IL-6, and IL-8 are elevated in nasal secretions during colds.
• Bradykinin production contributes to sore throat and rhinorrhea.
• The watery nasal discharge in the early phase is a mixture of nasal glandular secretions and plasma transudate.
• Nasal glands are activated through cholinergic stimulation.
• The nasal congestion in the late phase is caused by the dilation of large capacitance veins (sinuses) in the nasal epithelium, leading to swelling and blockage.
• The cough in later stages often arises from irritation of the larynx by mucus.
• Secondary bacterial infections by normal flora can lead to mucopurulent secretions.
• Severe cases can result in blockage of the sinus ostia or Eustachian tube, causing paranasal sinusitis or otitis media.

Coxsackie A Virus

• Belongs to the Picornaviridae family and the Enterovirus genus.
• Structure: Icosahedral, no envelope, stable at pH 3.
• Genome: (+) ssRNA, polyadenylated at the 3' end, with Vpg covalently linked to the 5' end. Contains 3' and 5' untranslated regions with an internal ribosome entry site (IRES) in the 5' UTR.
• Associated with childhood diseases: Herpangina and Hand Foot and Mouth disease (caused by A16).
• Coxsackie A21 and A24 can cause rhinovirus-like symptoms and a maculopapular rash.
• The VP1 protein at the vertices of the virion contains a canyon structure that binds to the cell receptor.
• Receptor for Coxsackie A: ICAM-1 expressed on epithelial cells, fibroblasts and endothelial cells; and decay accelerating factor CD55.
• Transmission: Fecal-oral route and by respiratory aerosols.
• Host cell range: Oropharynx epithelium for replication and skin following a secondary viremia.

This quiz explores the common cold, a prevalent respiratory illness characterized by various symptoms including nasal stuffiness and sore throat. Learn about the primary viruses responsible, such as Rhinovirus and Human Coronavirus, and the mechanisms through which these viruses infect the body and affect nasal passages.