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A cold is a mild viral infectious disease of the nose and throat, the upper respiratory system. It is different from influenza, a more severe viral infection of the respiratory tract that shows the additional symptoms of rapidly rising fever, chills, and body and muscle aches.
Symptoms of a cold include sneezing, sniffing, running/blocked nose (often these occur simultaneously, or one in each nostril), scratchy, sore, or phlegmy throat, coughing, headache, and a general feeling of unwellness; they last between 3 to 10 days, with residual coughing lasting up to 3 weeks. It is the most common of all diseases, infecting subjects at an average of slightly over one infection per year with greater than 3 infections per year not uncommon in some populations. Children and their caretakers are at a higher risk, probably due to the high population density of schools and the fact that transmission to family members or caretakers is highly efficient.
pathology of a cold
The common cold is caused by numerous viruses (mainly rhinoviruses, coronaviruses and also certain echoviruses, paramyxoviruses 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. These are transmitted from person to person by droplets resulting from coughs or sneezes. The droplets or droplet nuclei are either inhaled directly, or, 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, or eyes.
The virus enters the cells of the lining of the nasopharynx, and rapidly multiplies inside them. Nasopharynx being the area between the nose and throat is the central area infected. The mouth is not a major point of entry and virus transmission does not usually occur with kissing or swallowing, whereas the nose and the eye, through its nasolacrymal duct drainage into the nasopharynx are the major entrypoints. The specific localization in the nasopharynx and avoidance of the throat may be due to the low temperature here as well as the high concentration of cells with receptors needed by the virus. The virus enters the cell by binding to ICAM-1 receptors in these cells. The presence of ICAM-1 affects whether a cell will be infected and its concentration can be affected by various things including allergic rhinitis and some other irritants including rhinovirus itself and has been a major focal point in drug research into treatment. 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. Sneezes expel a significantly larger concentration of virus "cloud" than coughing. The "cloud" is partly invisible and falls at a rate slow enough to last hours - with part of the water droplets evaporating and leaving much smaller and invisible "droplet nuclei" in the air. Droplets by turbulent sneezing or coughing, or hand contact can also last for hours on surfaces, although less virus can be recovered from porous surfaces such as wood or paper towel than non-porous surfaces such as a metal bar. A sufferer is most infectious within the first three days of the illness. Symptoms however are not necessary for viral shedding or transmission as a percentage of symptomless subjects exibit virus in nasal swabs, likely controlling the virus at concentrations too low for them to have symptoms.
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 easily be infected by another cold virus to start the process all over again.
The term "cold" is misleading, if "cold" refers to climatic temperature, as the aetiology is viral. Climate may affect transmission by some means, such as by causing people to stay indoors and increasing the proximity to infected persons, but the cause of the infection remains primarily viral. Some allergies, bacterial respiratory infections and even climate changes can also cause common-cold-like symptoms that can last for days). Whether cold, or humid climate can affect transmission by other means, such as by affecting the immune system, or ICAM-1 receptor concentration, or simply increasing the amount and frequency of nasal secretions and frequency of hand to face contact has not yet been thoroughly tested and is not known. A person can best avoid colds by avoiding those who are ill and objects they touch, as well as keeping their immune system in top form by getting enough sleep, reducing stress, eating nutritious foods, and avoiding excess alcohol consumption. It is perhaps the case that "cold" refers to a "cold condition," i.e., the hot, cold, dry and wet "conditions" described by the ancient Roman physician Galen. Colds are somewhat more common in winter since during that time of the year people spend more time indoors in close proximity of others and ventilation is less, increasing the infection risk. Some factors influence the severity of symptoms, for instance psychological stress and position in the menstrual cycle. Also, weak health in general, or other pre-existing conditions such as allergies can be aggravated due to infection.
Bacteria that are normally present in the respiratory tract can take advantage of the weakened immune system during a common cold and produce a co-infection. Middle ear infection (in children) and bacterial sinusitis are common coinfections. A possible explanation for these coinfections is that strong blowing of the nose drives nasal fluids into those areas. The best way to blow the nose is keeping both nasal openings open when blowing and wiping rather than fully covering them, permitting pressure to dissipate partly here. This will reduce the pressure which could drive fluid into the ears or sinuses where it can cause infection.
The best way to avoid a cold is to avoid close contact with existing sufferers, to thoroughly wash hands regularly, and to avoid touching the face. Anti-bacterial soaps have no effect on the cold virus - it is the mechanical action of hand washing that removes the virus particles. In 2002, the Centers for Disease Control and Prevention recommended alcohol based hand gels as an effective method for reducing infectious viruses on the hands. However, as with standard handwashing, alcohol gels provide no residual protection from re-infection. In some countries, such as China and Japan, people with the common cold wear surgical masks out of courtesy to protect others.
Because of the large variety of viruses causing the common cold, vaccination is impractical.
best treatments for a cold
There is no cure for the common cold, i.e. there is no treatment that directly fights the virus. Only the body's immune system can effectively destroy the invader. A cold may be composed of several million viral particles, and typically within a few days the body begins mass producing a better tailored antibody that can prevent the virus from infecting cells, as well as white blood cells which destroy the virus through phagocytosis and destroy infected cells to prevent further viral replication. Furthermore the duration of infection is on the order of a few days to one week so at most a "cure" could hope to reduce the duration by only a few days.
Available treatments for cold therefore focus on relieving the symptoms.
For some people, even without these remedies, colds are relatively minor inconveniences and they can go on with their daily activities with tolerable discomfort. This discomfort has to be weighed against the price and possible side effects of the remedies, and the possibility, not yet scientifically proven, that by suppressing responses evolved to fight the cold, the symptom supressants may prolong the illness.
Common cold treatments include: analgesics such as NSAIDs such as aspirin or acetaminophen as well as localised versions targeting the throat (often delivered in lozenge form), nasal decongestants which reduce the inflammation in the nasal passages by constricting local blood vessels, cough suppressants (which work to suppress the cough reflex of the brain or by diluting the mucus in the lungs), and first-generation anti-histamines such as brompheniramine, chlorpheniramine, and clemastine (which reduce mucus gland secretion and thus combat blocked/runny noses but also may make the user drowsy). Second generation anti-histamines do not have a useful effect on colds.
A warm and humid environment and drinking lots of fluids, especially hot liquids, alleviate symptoms somewhat. Common home remedies include camomile tea, chicken soup, nebulized medicinal mixtures, hot compresses, mustard plasters, hot toddies, Licorice, vitamin C, and Echinacea. Although there have been scientific studies done on echinacea its effectiveness has not been demonstrated, whilst there is some evidence that Vitamin C will reduce the length of the infection (although it will not, as commonly believed, prevent contracting a cold in the first place). Coffee, or its active component, caffeine, has also been shown to improve mood and mental performance during rhinovirus infection. Hot beer is also recommended, and though it probably does little to fight the infection directly, at least it can help to a good night of relaxed sleep.
Zinc-containing preparates have been claimed to be effective in the treatment of cold infections. Some studies have attributed this to a placebo effect related to the strong and unpleasant taste of zinc preparates (Reference: Farr et al. (1987), while other studies claim that zinc lozenges are effective in reducing the duration and severity of common colds.
Zinc nasal sprays, however, claim clinical proof that they work. The trick seems to be threefold. One, the treatment has to be a nasal spray. Two, treatment should be started at the first sign of a cold before it has the chance to get established. Three, the type of zinc must be zinc gluconate usually labelled as zincum gluconicum. There have been several hundred lawsuits filed alleging that zinc nasal sprays may cause permanent damage to the sense of smell. References:
- Belongia EA, Berg R, Liu K. A randomized trial of zinc nasal spray for the treatment of upper respiratory illness in adults.
- American Journal of Medicine 2001, p.111, 103–108. Hirt M, Nobel S, Barron E. Zinc nasal gel for the treatment of common cold symptoms: a double-blind, placebo-controlled trial.
- Ear Nose Throat Journal 2000, p.79,778–781. Mossad SB. Effect of zincum gluconicum nasal gel on the duration and symptom severity of the common cold in otherwise healthy adults.
- QJM. 2003;96:35–43. Zicam, an over the counter (OTC) product of GumTech International, has developed a patent-pending solution in which zincum gluconicum nasal gel has been utilized to decrease symptoms and shorten the duration of the common cold up to 85%.
Antibiotics are ineffective against the common cold and all other viral infections. They are useful in treating any secondary bacterial infections that sometimes occur, but treatment with antibiotics before these coinfections develop is counterproductive, as it produces drug resistance, and can even promote infections by killing off normal bodily flora.
Prevention of transmission remains the best "treatment".
Posted by Staff at May 18, 2005 11:57 PMblog comments powered by Disqus