The common cold, or acute coryza, is an infection of the upper respiratory tract that can be caused by any one of more than
200 viruses. When infection occurs, the walls of the respiratory tract swell and produce excess mucus, giving rise to the typical cold symptoms of stuffy or runny nose, throat discomfort, malaise, and occasional coughing. Colds can produce fevers of up to 39¡ C (102¡ F) in infants and children, but such fevers in adults indicate that the infection is probably influenza. Most colds run their course in three to ten days, but infants and elderly persons are susceptible to complications such as sinusitis, ear inflammations, and pneumonia.
Because of the number of viruses involved, people do not develop immunity to colds as they do to many other viral diseases. Among the cold-causing viruses are paramyxoviruses (
parainfluenza and respiratory syncytial virus), picornaviruses (rhino-, echo-, and coxsackievirus), coronavirus, adenovirus, and influenza type C virus. Each virus also has numerous subsets; for example, the parainfluenza virus appears in four distinct forms, the fourth of which seems to cause only colds whereas the other three can cause croup, bronchiolitis, or pneumonia. More than 100
rhinoviruses have also been identified, and in 1985 one of them became the first animal virus to have its molecular structure mapped completely. Studies suggest that rhinoviruses trigger the release of natural proteins called kinins into the blood, causing vessels to expand and plasma to leak into other tissues. This irritates nerve endings and produces cold symptoms. All cold viruses are spread by direct contact or by airborne particles. They can become seasonally epidemicÑrhinoviruses in spring, summer, and fall, and parainfluenza and respiratory syncytial viruses more commonly in late fall and winter.
Colds are treated with rest and fluids, in addition to antihistamines, decongestants, and cough medicines as needed. Aspirin is recommended only when symptoms are severe, because it increases viral shedding and makes the sufferer more contagious. Vaccines are of little use in prevention because so many kinds of viruses are involved. Vitamin C, despite claims, does not prevent colds, but large doses may lessen symptoms. Research suggests that interferon could prevent the spread of colds and may prove useful to persons at high risk for complications. In 1988, a drug called R61837 was found useful in preventing colds in persons exposed to some of the rhinoviruses.