What causes a common cold?
The common cold is caused by numerous viruses (mainly rhinoviruses, coronaviruses and also certain echoviruses and coxsackieviruses) infecting the upper respiratory system. Several hundred cold causing viruses have been described, and a virus can mutate to survive, ensuring that any cure is still a long way off if not impossible. These are transmitted from person
to person by droplets resulting from coughs or sneezes. The droplets are either inhaled directly, or, more commonly, transmitted from hand to hand via handshakes or objects such as door knobs, and then introduced to the nasal passages when the hand touches the nose, mouth or eyes.
Of the viruses that cause a cold, the most commonly occurring subtype is a group that lives in the nasal passages known as the "rhinovirus." Other less common cold viruses include coronavirus, adenovirus, and respiratory syncytial virus (RSV). The virus enters the cells of the lining of the nose and throat, and rapidly multiplies inside them. Ninety-five percent of people exposed to a cold virus become infected, although only 75% show symptoms. The symptoms start 1-2 days after infection. They are a result of the body's defense mechanisms: sneezes, runny nose and coughs to expel the invader, and inflammation to attract and activate immune cells. The virus takes advantage of sneezes and coughs to infect the next person before it is killed by the body's immune system. A sufferer is most infectious within the first three days of the illness.
After a common cold, a sufferer develops immunity to the particular virus encountered. Because of the large number of different cold viruses however, this immunity is of limited use and a person can easiy be infected by another cold virus to start the process all over again.
Contrary to popular belief, the vast majority of cold viruses do not spread through the air and seldom are transmitted from airborne particles expelled when someone with a cold coughs or sneezes. Children usually get colds from other children. When a new strain is introduced into a school or day care, it quickly travels through the class. Colds can occur year-round, but they occur mostly in the winter (even in areas with mild winters). In areas where there is no winter, colds are most common during the rainy season.
When someone has a cold, their runny nose is teeming with cold viruses. Sneezing, nose-blowing, and nose-wiping spread the virus. You can catch a cold by inhaling the virus if you are sitting close to someone who sneezes, or by touching your nose, eyes, or mouth after you have touched something contaminated by the virus. People are most contagious for the first 2 to 3 days of a cold, and usually not contagious at all by day 7 to 10.
Colds mainly spread when a person's hands come in contact with nasal secretions from an infected person. These secretions contain cold viruses. When the person touches his mouth, nose, or eyes, the viruses gain entry to the body and produce a new cold. Less often, colds are spread when a person breathes air that contains droplets that were coughed or sneezed out by an infected person. A cold is most contagious in the first 1 or 2 days after symptoms develop. The primary means of spreading a cold is through hand-to-hand contact or from objects that have been touched by someone with a cold.
The typical transmission occurs when a cold sufferer rubs his or her nose and then, shortly thereafter, shakes hands with someone who, in turn, touches his or her own nose or eyes. Alternatively, virus transmission often occurs via doorknobs and other hard surfaces, such as subway handrails, grocery carts, office telephones, and computer keyboards. Finally, cold viruses can be spread through inanimate objects (door knobs, telephones, toys) that become contaminated with the virus. This is a common method of transmission in child care centers. If a child with a cold touches his runny nose, then plays with a toy, some of the virus may be transferred to the toy. When another child plays with the toy a short time later, he may pick up some of the virus on his hands. The second child then touches his contaminated hands to his eyes, nose, or mouth and transfers some of the cold virus to himself. |
