Rhinovirus - The Common Cold
Introduction: Rhinovirus, pictured above, is best known as the common cold. It is a member of the picornaviridae family along with more virulent viruses such as polio and hepatitis A. The viruses of this family are characterized as small (20-30nm genome) positive polarity RNA viruses consisting of one genome segment and a nonenveloped capsid. Unlike the its more lethal relatives, Rhinovirus is designed to attack a host numerous times during their lifetime. It is the perfect pathogen. It is estimated that adults suffer from 2 to 4 infections with the virus each year. The statistics below show the toll that the virus has on the United States Population:
Contrary to popular belief, there is no valid clinical evidence that exposure to cold or moisture will result in infection.
Entry: Primary infection occurs in the nasal mucosa and occasionally the conjunctiva. Once exposed to the epithelial cells, the virus attempts to bind to intracellular adhesion molecule-1 (ICAM1).
ICAM-1 is regularly used by the immune system to bind endothelial cells to leukocytes. However, as the picture above shows, Rhinovirus is able to take advantage of this property and recognizes it with its own receptors. The invasion of the virus can upregulate the immune system and cause more ICAM-1 receptors to become available and increase suseptibility. However, the body has developed natural defenses for dealing with the pathogen.
Rhinovirus is first limited by the number of receptors that are available to it. Sialic acid glycoproteins, normally contained in mucus, are able to can compete with the viral receptors and diminish or prevent the binding of the pathogen.  To infect the host, the virus must not be swept away in the mucus, neutralized by IgA, or be destroyed by recruited macrophages. Rhinovirus is also acid labile which means that it is unable to withstand the harsh conditions in the gasterol intestinal tract. The key feature to Rhinovirus is its need for a low temperature environment, about 33 degrees Celsius. The body temperature of 37 degrees Celsius is to extereme for the pathogen. Therefore it is limited to upper respiratory infection and can not become systemic.
Damage: While in the body, Rhinovirus does little or no tissue damage. Below is a picture of Rhinovirus infected cells. Many of the symptoms, such as coryza, sneezing, lacrimation, irritated nasopharynx, headache, sore throat, and chills are a result of the stimulated immune response. The constant cytokines cause inflammation of the respiratory tract. In some cases lyrangitis, tracheitis, and bronchitis can result. More importantly, the Rhinovirus weakens the immune system and allows secondary bacterial infections like sinusitis and in rare cases pneumonitis to take hold.
Human diploid fibroblasts infected with Rhinovirus (100X). Courtesy © Danny L. Wiedbrauk, William Beaumont Hospital, Royal Oak, Michigan USA.
Treatment: The major problem with Rhinovirus is that being infected with one strand will not result in cross immunity to another serotype. There are a few different antiviral drugs on clinical trials for Rhionvirus right now. One such product,...