The common cold is a viral infection that occurs in the upper respiratory system. Colds are generally caused by a rhinovirus, although other viruses, such as parainfluenza viruses and corona virus, may also be responsible, they are among the most common viral diseases.

Initial Infection

Cold viruses are transmitted from one person to another by droplets that are expelled into the air when an infected person coughs or sneezes. These droplets can remain suspended in the air for hours after they are expelled and are easily inhaled by potential hosts. Some droplets also fall onto surfaces, such as telephones or door handles, that many others come into contact with. Once touched, the cold virus is transferred to the person's hand, which can then come into contact with the mouth, thereby infecting the "host."

Once within the host, the virus will fuse to the plasma membrane of a permissive cell within the respiratory track, particularly those of the nose, mouth and throat.

Cellular Stage

The virus will then enter into the cytoplasm of the cell, and then to the nucleus of the cell. The virus gains entry to the nucleus and deposits viral DNA. It then replicates its genome within the nucleus. Once complete, virus particles will leave the cell, entering into the surrounding tissues and infecting other cells within the host. This is a cyclical process. The incubation period lasts from one to three days.

Infectious Stage

Once the virus has proliferated, it will begin to be shed from the mucous membranes into the saliva and the nasal discharge of the host. The infectious stage begins about one day before the presentation of symptoms and may continue for up to a week.

Signs and Symptoms

Two to three days after initial infection, symptoms will begin to present, usually starting with a sore throat. Symptoms will progress to include a runny nose, sneezing, coughing and nasal congestion. Body aches, general malaise and weakness may also occur. Fever rarely occurs in the common cold. Symptoms generally resolve within a few days but may last as long as two weeks.

Diagnosis and Treatment

Diagnosis can be made by observing the specific clinical manifestations of the disease. For the most part, a cold will generally resolve on its own. Palliative care, including rest, good nutrition, and the use of decongestants, antihistamines, pain relievers, and cough syrups may help to relieve the effects of most symptoms.

Recently, the use of preparations of zinc, the herb echinacea, and high doses of vitamin C have been popular, although studies have proved inconclusive about these potential treatments.

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