Infectious Disease Of The Mouth

Infectious Diseases Of the Oral Cavity, Respiratory System and GastroIntestinal (GI) Tract Infectious diseases are caused by entry into the body of infectious agents commonly called germs. Alain Jon Candido

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Common cold From Wikipedia, the free encyclopedia

Acute viral nasopharyngitis, or acute coryza, usually known as the common cold, is a highly contagious, viral infectious disease of the upper respiratory system, primarily caused by picornaviruses (including rhinoviruses) or coronaviruses. Common symptoms are sore throat, runny nose, nasal congestion, sneezing and cough; sometimes accompanied by 'pink eye', muscle aches, fatigue, malaise, headaches, muscle weakness, and/or loss of appetite. Fever and extreme exhaustion are more usual in influenza. The symptoms of a cold usually resolve after about one week, but can last up to two. Symptoms may be more severe in infants and young children. Although the disease is generally mild and self-limiting, patients with common colds often seek professional medical help, use over-the-counter drugs, and may miss school or work days. The annual cumulative societal cost of the common cold in developed countries is considerable in terms of money spent on remedies, and hours of work lost. The primary method to prevent infection is hand-washing to minimize person-to-person transmission of the virus. There are no antiviral drugs approved to treat or cure the infection. Most available medications are palliative and treat symptoms only. Megadoses of vitamin C, preparations from echinacea, and zinc gluconate have been studied as treatments for the common cold although none has been approved by the Food and Drug Administration or European Medicines Agency.

Pathology Epidemiology Upper respiratory tract infections are the most common infectious diseases among adults and teens, who have two to four respiratory infections annually. Children may have six to ten colds a year (and up to 12 colds a year for school children). In the United States, the incidence of colds is higher in the fall and winter, with most infections occurring between September and April. The seasonality may be due to the start of the school year, or due to people spending more time indoors (thus in closer proximity with each other) increasing the chance of transmission of the virus.

Virus Common colds are most often caused by infection by one of the more than 100 serotypes of rhinovirus, a type of picornavirus. Other viruses causing colds are coronavirus, human parainfluenza viruses, human respiratory syncytial virus, adenoviruses, enteroviruses, or metapneumovirus. Due to the many different types of viruses, it is not possible to gain complete immunity to the common cold.

Transmission The common cold virus is transmitted between people by one of two mechanisms: •

in aerosol form generated by coughing, sneezing.

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from contact with the saliva or nasal secretions of an infected person, either directly or from contaminated surfaces.

Symptoms are not necessary for viral shedding or transmission, as a percentage of asymptomatic subjects exhibit viruses in nasal swabs. The virus enters the cells of the lining of the nasopharynx (the area between the nose and throat), and rapidly multiplies. The major entry point is normally the nose, but can also be the eyes (in this case drainage into the nasopharynx would occur through the nasolacrimal duct).

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Symptoms After initial infection, the viral replication cycle begins within 8 to 12 hours. Symptoms can occur shortly thereafter, and usually begin within 2 to 5 days after infection, although occasionally in as little as 10 hours after infection. The first indication of a cold is often a sore or scratchy throat. Other common symptoms are runny nose, congestion, sneezing and cough. These are sometimes accompanied by muscle aches, fatigue, malaise, headache, weakness, or loss of appetite. Colds occasionally cause fever and can sometimes lead to extreme exhaustion. (However, these symptoms are more usual in influenza, and can differentiate the two infections.) The symptoms of a cold usually resolve after about one week, but can last up to 14 days, with a cough lasting longer than other symptoms. Symptoms may be more severe in infants and young children, and may include fever and hives.

Prevention The best way to avoid a cold is to avoid close contact with existing sufferers; to wash hands thoroughly and regularly; and to avoid touching the mouth and face. Anti-bacterial soaps have no effect on the cold virus; it is the mechanical action of hand washing with the soap 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 of health care workers. As with hand washing with soap and water, alcohol gels provide no residual protection from re-infection. The common cold is caused by a large variety of viruses, which mutate quite frequently during reproduction, resulting in constantly changing virus strains. Thus, successful immunization is highly improbable.

Exposure to cold weather Although common colds are seasonal, with more occurring during winter, experiments so far have failed to produce evidence that short-term exposure to cold weather or direct chilling increases susceptibility to infection, implying that the seasonal variation is instead due to a change in behaviors such as increased time spent indoors at close proximity to others. With respect to the causation of cold-like symptoms, researchers at the Common Cold Centre at the Cardiff University conducted a study to "test the hypothesis that acute cooling of the feet causes the onset of common cold symptoms." The study measured the subjects' self-reported cold symptoms, and belief they had a cold, but not whether an actual respiratory infection developed. It found that a significantly greater number of those subjects chilled developed cold symptoms 4 or 5 days after the chilling. It concludes that the onset of common cold symptoms can be caused by acute chilling of the feet. Some possible explanations were suggested for the symptoms, such as placebo, or constriction of blood vessels, however "further studies are needed to determine the relationship of symptom generation to any respiratory infection."

Treatment As there is no medically proven and accepted medication directly targeting the causative agent, there is no cure for the common cold. Treatment is limited to symptomatic supportive options, maximizing the comfort of the patient, and limiting complications and harmful sequelae. The common cold is self-limiting, and the host's immune system effectively deals with the infection. Within a few days, the body's humoral immune response begins producing specific antibodies that can prevent the virus from infecting cells. Additionally, as part of the cell-mediated immune response, leukocytes destroy the virus through phagocytosis and destroy infected cells to prevent further viral replication. In healthy, immunocompetent individuals, the common cold resolves in seven days on average.

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Palliative care The National Institute of Allergy and Infectious Diseases suggests getting plenty of rest, drinking fluids to maintain hydration, gargling with warm salt water, using cough drops, throat sprays, or over-thecounter pain or cold medicines. Saline nasal drops may help alleviate congestion. The American Lung Association recommends avoiding coffee, tea or cola drinks that contain caffeine and avoiding alcoholic beverages, saying that both caffeine and alcohol cause dehydration. However, a study reported in 2000, as well as the U.S. Institute of Medicine in 2004, say that caffeinated beverages and non-caffeinated beverages equally meet the need for fluids.

Antibiotics Antibiotics, targeted primarily to microorganisms like bacteria and fungus, do not have any beneficial effect against the common cold. Their use in cases of common cold infection is ineffective as they have no effect on viruses.

Antivirals There are no approved antiviral drugs for the common cold. ViroPharma and Schering-Plough are developing an antiviral drug, pleconaril, that targets picornaviruses, the viruses that cause the majority of common colds. Pleconaril has been shown to be effective in an oral form. Schering-Plough is developing an intra-nasal formulation that may have fewer adverse effects.

Over-the-counter symptom medicines There are a number of effective treatments which, rather than treat the viral infection, focus on relieving the symptoms. For some people, 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. •

analgesics such as aspirin or paracetamol (acetaminophen), as well as localised versions targeting the throat (often delivered in lozenge form)

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nasal decongestants such as pseudoephedrine or oxymetazoline which reduce the inflammation in the nasal passages by constricting dilated local blood vessels

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cough suppressants such as dextromethorphan which suppress the cough reflex.

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first-generation anti-histamines such as brompheniramine, chlorpheniramine, diphenhydramine 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.