The common cold is a viral infectious disease that infects the upper respiratory system. It is also known as acute viral rhinopharyngitis, or acute coryza. Being the most common infectious disease in humans, the cold is mainly caused by coronaviruses or rhinoviruses.
Rhinoviruses(common cold) have single-stranded positive sense RNA genomes of between 7200 and 8500 nt in length. At the 5' end of the genome is a virus-encoded protein, and like mammalian RNA, 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. The viral proteins are translated as a single, long polypeptide, which is cleaved into the structural and nonstructural viral proteins. Human rhinoviruses are composed of a capsid, that contains four viral proteins VP1, VP2, VP3 and VP4. VP1, VP2, and VP3 form the major part of the protein capsid. The much smaller VP4 protein has a more extended structure, and lies at the interface between the capsid and the RNA genome. There are 60 copies of each of these proteins assembled as an icosahedron. Antibodies are a major defence against infection with the epitopes lying on the exterior regions of VP1-VP3.
While the cause of the common cold has only been identified since the 1950s, the disease has been with humanity since ancient times. Its symptoms and treatment are described in the Egyptian Ebers papyrus, the oldest existing medical text, written before the 16th century BCE. The name "cold" came into use in the 16th century, due to the similarity between its symptoms and those of exposure to cold weather.
While the cause of the common cold has only been identified since the 1950s, the disease has been with humanity since ancient times. Its symptoms and treatment are described in the Egyptian Ebers papyrus, the oldest existing medical text, written before the 16th century BCE. The name "cold" came into use in the 16th century, due to the similarity between its symptoms and those of exposure to cold weather. In the United Kingdom, the Common Cold Unit was set up by the Medical Research Council in 1946 and it was where the rhinovirus was discovered in 1956. In the 1970s, the CCU demonstrated that treatment with interferon during the incubation phase of rhinovirus infection protects somewhat against the disease, but no practical treatment could be developed. The unit was closed in 1989, two years after it completed research of zinc gluconate lozenges in the prophylaxis and treatment of rhinovirus colds, the only successful treatment in the history of the unit.
The common cold is the most common human disease and affects people all over the globe. Adults typically have two to five infections annually, and children may have six to ten colds a year (and up to twelve colds a year for school children). Rates of symptomatic infections increase in the elderly due to declining immunity. Native Americans and Inuit are more likely to be infected with colds and develop complications such as otitis media than Caucasians. This may be explained by issues such as poverty and overcrowding rather than by ethnicity.
Humans are the only known reservoir of the common cold virus. The common cold virus is typically transmitted via airborne droplets (aerosols), direct contact with infected nasal secretions, or fomites (contaminated objects). Which of these routes is of primary importance has not been determined; however, hand-to-hand and hand-to-surface-to-hand contact seems of more importance than transmission via aerosols.
The common cold virus is a viral infectious disease of the upper respiratory tract that primarily affects the nose. The throat, sinuses, and voice box may also be affected. Signs and symptoms may begin less than two days following exposure. They include coughing, sore throat, runny nose, sneezing, headache, and fever. People usually recover in seven to ten days.[4] Some symptoms may last up to three weeks. In those with other health problems, pneumonia may occasionally develop.
As the common cold is a virus, it can not inflict much damage, still being its most common form, the primary form. For ms t people when suffering from a common cold, they may experience a runny nose, a sore throat and some headaches.
The common cold is generally mild and self-limiting with most symptoms generally improving in a week. Half of cases go away in 10 days and 90% in 15 days. Severe complications, if they occur, are usually in the very old, the very young, or those who are immunosuppressed. Secondary bacterial infections may occur resulting in sinusitis, pharyngitis, or an ear infection. It is estimated that sinusitis occurs in 8% and ear infection in 30% of cases.
The typical symptoms of a cold include a cough, a runny nose, nasal congestion and a sore throat, sometimes accompanied by muscle ache, fatigue, headache, and loss of appetite. A sore throat is present in about 40% of the cases and a cough in about 50%, while muscle ache occurs in about half. In adults, a fever is generally not present but it is common in infants and young children. The cough is usually mild compared to that accompanying influenza. While a cough and a fever indicate a higher likelihood of influenza in adults, a great deal of similarity exists between these two conditions. A number of the viruses that cause the common cold may also result in asymptomatic infections. The colour of the sputum or nasal secretion may vary from clear to yellow to green and does not indicate the class of agent causing the infection.
The symptoms of the common cold are believed to be primarily related to the immune response to the virus. The mechanism of this immune response is virus specific. For example, the rhinovirus is typically acquired by direct contact; it binds to human ICAM-1 receptors through unknown mechanisms to trigger the release of inflammatory mediators. These inflammatory mediators then produce the symptoms. It does not generally cause damage to the nasal epithelium. The respiratory syncytial virus (RSV), on the other hand, is contracted by direct contact and airborne droplets. It then replicates in the nose and throat before frequently spreading to the lower respiratory tract. RSV does cause epithelium damage. Human parainfluenza virus typically results in inflammation of the nose, throat, and bronchi. In young children when it affects the trachea it may produce the symptoms of croup due to the small size of their airways.
No medications or herbal remedies have been conclusively demonstrated to shorten the duration of infection. Treatment thus comprises symptomatic relief. Getting plenty of rest, drinking fluids to maintain hydration, and gargling with warm salt water are reasonable conservative measures. Much of the benefit from treatment is, however, attributed to the placebo effect.
The only useful ways to reduce the spread of cold viruses are physical measures such as hand washing and face masks; in the healthcare environment, gowns and disposable gloves are also used. Isolation or quarantine is not used as the disease is so widespread and symptoms are non-specific. Vaccination has proved difficult as there are many viruses involved and they mutate rapidly. Creation of a broadly effective vaccine is, thus, highly improbable. Regular hand washing appears to be effective in reducing the transmission of cold viruses, especially among children. Whether the addition of antivirals or antibacterials to normal hand washing provides greater benefit is unknown. Wearing face masks when around people who are infected may be beneficial; however, there is insufficient evidence for maintaining a greater social distance. Zinc supplements may help to reduce the prevalence of colds. Routine vitamin C supplements do not reduce the risk or severity of the common cold, though they may reduce its duration. Gargling with water was found useful in one small trial.
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