The common cold is a viral disease, with rhinoviruses being by far the most common cause (30–50% of all infections). Other causes of colds include the coronavirus (10–15% of infections), influenza (5–15% of infections) as well as human parainfluenza viruses, human respiratory syncytial virus, adenoviruses, enteroviruses, and metapneumovirus. In fact, over 200 serolocially distinct viral types can cause colds, with coronaviruses being particularly prevalent in adult colds.
The viruses that cause colds in humans tend to evolve rapidly through continuous mutations, as a result it is impossible to gain complete immunity to colds.
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The common cold is a droplet-borne infection and can be transmitted by breathing in tiny particles that an infected person emits when they cough or sneeze. It has also been demonstrated that cold viruses can be spread by touching contaminated objects and surfaces, or by brief contact of hands. Spending time in an enclosed area with an infected person or in close contact with an infected person. If contaminated fingers are then used to touch the nose, mouth or eyes, the virus can be transmitted from the surface of the hands to the tissues of the upper respiratory tract, where it can cause an infection. One of the most comon folkloric explanation for the diesese is that cooling the body can trigger a cold. This hypothesis is controversial, though there is some experimental evidence to support this. Though other studies refute the finding.
Interestingly, getting fewer than seven hours of sleep per night has been associated with a risk three times higher of developing an infection when exposed to a rhinovirus, compared to those who sleep more than eight hours per night. Common colds are seasonal, occurring more frequently during winter outside of tropical zones though this may be more due to spending moe time indoors, thus leading to more communication with infected people and the immunosuppressive effects of the winter months.
Low humidity also increases viral transmission rates. This may be due to increased evaporation of water in low humudity, which allows small viral droplets to disperse further an stay in the air longer.
It is the immune response that causes the symptoms of a cold. As a result, those with stronger immune systems are more likely to develop symptomatic colds. Thus attempts to 'boost' the immune system will actually make cold symptoms worse, though it may decrease the length of infection. 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. The first symptom of a cold is typically an itchy or scratchy throat that may develop 24 to 48 hours before other symptoms. Prevention of ColdsFairly obvously, the most successful method to prevent colds is to stay away from infected people and places where infected people have been. Regular hand washing will also reduce the transmission of cold viruses. It is also important that those infected also wash their hands regularly, a this greatly reduces the number of viral particles and reduces the risk of transmission by contact. The common cold is caused by a virus, as a result anti-bacterial hand washes are no more effective at eliminating cold viruses than ordinary soap. Indeed, hand washing with a plain bar of soap and water is recommneded. This is because the mechanical acton of rubbing the hand with the soap, rinsing the hands whilst rubbing together and then drying on towels physically removes viral particles from the hands. To date, there is no effective vaccine against the common cold. The problem being that colds are produced by a large variety of viruses that mutate rapidly, as a result the likelihood of creating a broadly-effective vaccine is very remote. |
There are currently no medications that have been conclusively demostrated to shorten the duration of infection in people with cold symptoms. As a result, treatments of colds involves easing the symptoms of fever, headaches, sore muscles, sore throats and coughs.
Treatments that help alleviate symptoms include simple analgesics and antipyretics such as ibuprofen and acetaminophen / paracetamol. Evidence does not show that cough medicine is any more effective than simple analgesics and is not recommended for use in children due to a lack of evidence supporting its effectiveness and the potential for harm.
The symptoms of a runny nose can be reduced by antihistamines (though these also produce drowsiness and other side-effects). Decongestants such as pseudoephedrine are effective in adults but there is insufficient evidence to support their use in children. However, anticholinergics such as Ipratropium nasal spray can reduce the symptoms of runny nose with less side effects.
Zinc may inhibit rhinovirus replication and reduce inflammation. Trials have found that zinc supplements can somewhat reduce the severity and duration of common cold symptoms when taken by otherwise healthy adults within 24 hours of onset of symptoms. In general, however, the levels of zinc required to be clinically effective border on the toxic.
Routine vitamin C supplementation does not reduce the incidence or severity of the common cold in the general population, though it may reduce the duration of illness.
Antibiotics have NO EFFECT against viral infections and thus have no effect in treating the common cold.
The human rhinovirus is the most common viral infective agent in humans and is the chief cause of the common cold. Rhinovirus infection proliferates in temperatures between 33–35°C, and this may be why it occurs primarily in the nose. Rhinovirus is a species in the genus Enterovirus of the Picornaviridae family of viruses
There are 99 recognized types of Human rhinoviruses that differ according to their surface proteins. They are amongst the smallest viruses, with diameters of about only 30 nanometers.
The name rhinovirus derives from the Greek ῥίς, ῥινός (gen.), meaning 'nose'. Thus rhinoviruses are 'viruses of the nose'.
Rhinoviruses have single-stranded positive sense RNA genomes of between 7.2 and 8.5 kb in length. At the 5' end of the genome is a virus-encoded protein, and like mammalian mRNA, there is a 3' poly-A tail. Structural proteins are encoded in the 5' region of the genome and non structural at the 3' end. This is the same for all picornaviruses. The viral particles themselves are not enveloped and are icosahedral in structure.
Human rhinoviruses are composed of a capsid, that contains four viral proteins VP1, VP2, VP3 and VP4.
The primary route of entry for Human rhinoviruses is the upper respiratory tract. Afterward, the virus binds to ICAM-1 (Inter-Cellular Adhesion Molecule 1) also known as CD54 (Cluster of Differentiation 54) receptors on respiratory epithelial cells. As the virus replicates and spreads, infected cells release distress signals known as chemokines and cytokines (which in turn activate inflammatory mediators).
Infection occurs rapidly, with the virus adhering to surface receptors within 15 minutes of entering the respiratory tract. Just over 50% of symptomatic individuals will experience symptoms within 2 days of infection. Only about 5% of cases will have an incubation period of less than 20 hours, and, on the other end, it is expected that 5% of cases would have an incubation period of greater than four and a half days.
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