The Common Cold

Bacteriology at UW-Madison

The Microbial World

Lectures in Microbiology by Kenneth Todar PhD University of Wisconsin-Madison Department of Bacteriology

The Common Cold

The common cold is probably the most prevalent infectious disease that occurs in humans. It is estimated that there are up to a billion colds per year in the United States. Children have about 6 to 10 colds a year. This is due to lack of acquired immunity and because children are often in close contact with each other in daycare centers and schools. Adults average about 2 to 4 colds a year, although the range varies widely. Women, especially those 20 to 30 years of age, have more colds than men, possibly because of their closer contact with children. On average, people older than 60 have fewer than one cold a year.

Everyone is familiar with the symptoms of the common old, which are sore throat, cough, conjunctivitis and increased flow of mucus. Sneezing and coughing are common; fever is rare, except in young children. Usually, the infection is mild, lasting only a few days. However, it is a leading cause of doctor visits and missed days from school and work. According to the CDC, 22 million school days are lost annually in the United States due to the common cold.

Symptoms of the common cold http://www.cardiff.ac.uk/biosi/associates/cold/info.html Colds are diagnosed based on their symptoms. However, when the symptoms present, several diagnostic problems are met because the symptoms are difficult to distinguish from noninfectious rhinitis (i.e., allergy), or they may be prodromal symptoms of other more serious respiratory group diseases such as diphtheria, whooping cough, measles, or influenza.

Viruses that Cause Colds

The common cold (rhinitis or coryza) is caused by several groups of viruses, although rhinoviruses have gotten the most attention. Other cold-causing viruses include adenoviruses, coronaviruses, respiratory syncytial virus (RSV), parainfluenza and influenza viruses. Rhinoviruses seldom produce serious illness, but others such as parainfluenza and RSV can produce severe respiratory illness in infants and young children.

Rhinoviruses (from the Greek rhin, meaning "nose") cause an estimated 30 to 35 percent of all adult colds, and are most active in early fall, spring, and summer. More than 100 distinct serotypes (antigenic types) have been identified. Rhinoviruses grow best at temperatures of about 91 degrees Fahrenheit, the temperature inside the human nose.

Rhinovirus 14 as solved by x-ray crystallography. Rhinoviruses are picornaviruses - small, icosahedral, nonenveloped, sinlge stranded (+)RNA viruses.

Coronaviruses are apparently the second leading cause of adult colds. They bring on colds primarily in the winter and early spring. Of the more than 30 kinds, three or four infect humans. The 2003 SARS virus is a coronaviruses. Unlike rhinoviruses, coronaviruses are difficult to grow in the laboratory, so they have not been studied to the same extent as the rhinoviruses.

Approximately 10 to 15 percent of adult colds are caused by viruses which are also responsible for other, more severe illnesses. These include adenoviruses, coxsackieviruses, influenza viruses, parainfluenza viruses, respiratory syncytial virus and enteroviruses. T

Actually, the causes of 30 to 50 percent of adult colds, are unidentified and presumed to be viral.

Transmission of Colds

Quite a few studies have been done on the transmission of cold viruses, especially caused by Rhinoviruses. These viruses are usually transmitted by contact with an infected person's contaminated skin (e.g. hand) or a contaminated environmental surface, then touching your eyes or nose, which are the routes of inoculation. Contaminated environmental surfaces are everywhere in the home, dorm and public places, and include objects such as telephones, stair rails, door entrances, shopping carts, money, etc., so the best way to avoid transmission is to wash your hands frequently and wait until you have clean hands to touch your eyes or nose. Although colds can be spread by large particles expelled by coughing or sneezing at close range, the viruses apparently are not spread by kissing.

Despite the fact that few of us escape from at least one cold a year, the common cold viruses are not highly contagious. Under laboratory conditions, when healthy "volunteers" were sequestered with an individual with an active cold, it proved remarkably difficult for the virus to spread from person to person. To catch a cold, you really have to get a droplet of mucus from an infected person's nose to your nose.

Infection by cold viruses usually occurs in the home or the childrens' school or daycare center. Young children are the major reservoir of common cold viruses, and adults in contact with children are most exposed to infection.

The incubation period for the common cold is usually around two days. The patient is most infective during the early symptoms of sneezing, coughing and runny nose. The virus replicates in the cells lining the nose. This precipitates a cascade of inflammatory events and an immune response that results in cellular release of chemical mediators and cytokines that presumably contribute to the symptoms. Mediators, such as histamine, bradykinin and prostaglandins, and cytokines, such as Interleukin 1 and Interleukin 2, are components of the inflammatory exudate.

Colds occur at all times of the year although there are two peaks of increased incidence or "cold seasons": one is in April-May and the other in September-October. There is a correlation between incidence of colds and cold weather, but no satisfactory explanation has been provided. Chilling of the body lowers the host resistance, and chilling of the nose (as breathing colder air) may create a more permissive growth temperature for the viruses.

Treatment of Colds

A cure for the common cold has been elusive. Most colds are self limiting and will go away within a few days. However, there are many treatments and over-the counter drugs and remedies available to relieve the symptoms of a cold. These undoubtedly represent a huge profitable market for the pharmaceutical industry and include the following:

Analgesics/Antipyretics such acetominophen (tylenol) aspirin, ibuprophen (Advil), and naproxyn sodium (Naprosyn) are useful for reducing the pain and fever associated with the common cold.

Decongestants such as pseudoephedrine hydrochloride (Sudafed) decrease nasal secretions and congestion.

Expectorants such as guaifenesin (Robitussin) thin respiratory secretions and decrease overall coughing.

Antitussives are opiate derivatives, such as codeine and dextromethorphan hydrobromide (Robitussin DM) that are useful in suppressing coughing by depressing the nervous system.

Antihistimines such as chlorpheniramine maleate (Chlor-Trimeton), brompheniramine maleate (Dimetapp), Dipheniramine hydrochloride (Benadryl), and triprolidine hydrochloride (Actifed) have been used to treat symptoms, since they theoretically block release of the inflammatory agent, histamine.

Antivirals to human rhinoviruses have been recently developed for the treatment of the common cold. The mechanisms of these drugs usually involve prevention of viral attachment to a cognate cell receptor.

Alternative Medicines

While traditional medicines have been shown to relieve the symptoms of the common cold, there is mounting evidence that several alternative treatments can prevent the onset or shorten the duration of common cold symptoms. Most alternative medicines appear to have no serious side effects, especially if regularly marketed products are used. Some treatments that have been found to be effective include:

Zinc lozenges have been shown to reduce the duration of the common cold. Zinc deficiency has been linked to a variety of immune system abnormalities.

Echinacea is a daisy-like purple wild flower found across the United States. It has been shown to stimulate white blood cell activity.

Garlic, in the form of garlic nose drops, has also been shown to have prophylactic activity.

Vitamin C has been used for treating and preventing colds, although its efficacy has been questioned. Vitamin C is known to be a stimulator of the antiviral cytokine Interferon, which prevents viral replication.

Menthol and Eucalyptus oils can provide relief from nasal congestion by causing a cool sensation in the nose. Local anesthetic action also helps relieves sore throat and coughs. These oils also have antimicrobial activity that may help to prevent infection of the upper respiratory tract.

Prevention of Colds

The Stanford Coronavirus Group recommends the top ten ways to avoid a cold.

10. Stress Reduction. Strong links have been drawn between stress and immune system functioning. The more stressed you are, the weaker your immune system will be and the more likely you are to develop symptoms.

9. Make sure your environment is not too dry. Keep the air moist enough so that your nasal passages do not dry out. Consider using a humidifier.

8. Be careful with items such as money, pens, and keypads in public places. They are all potential sources of infection.

7. Take precaution when flying on commercial airlines. The recirculation systems aboard planes has been implicated in the spread of airborne infectious diseases

6. Garlic nose drops have been known to kill the viruses that cause colds (if you don't mind the smell of garlic!). In his book The Healing Power of Garlic Paul Bergner suggests crushing some garlic to obtain juice, adding ten parts water and mixing well.

5. If someone in your household is sick, let them use separate items, such as hand towels, from those who are healthy.

4. Keep your feet warm. Cold feet cannot cause a viral infection, but they can undermine your defenses thereby opening the door to them.

3. Keep your nasal passages clear and breathe through your nose. Your nose is able to filter out airborne dust and germs.

2. Alternative medications. Recent studies have shown that alternative medications such as zinc and Echinacea may help prevent the onset of colds.

1. Never put your hands in your eyes or to your nose without washing them first.

Vaccines for the Common Cold

Vaccines are not forthcoming because colds are caused by over 200 different viruses, colds are not life-threatening, and there is too much money to be made off of the relief of symptoms.

Websites for the Common Cold
Cardiff(UK): General Common Cold Information
NIAID: The Common Cold
Quanta-Gaia: Beating Colds and Flu
Stanford Coronavirus Group