|MadSci Network: Virology|
The common cold can be caused by a variety of viruses. It is principally caused by rhinovirus and coronavirus infections; but respiratory syncytial virus and parainfluenza viruses may also cause common cold in adults (whereas they cause mainly lower respiratory tract infection, such as bronchiolitis or pneumonia, in children.) As would be expected/experienced by most people, transmission of rhinovirus and coronavirus infection depends on prolonged close contact, and is by droplet spread, or via contaminated nasal secretion carried by the subject's hand/body. The incubation period, i.e. infectious while asymptomatic, ranged from 1to 5 days. And it has been estimated that a susceptible adult has a 50% chance of being infected by 4 days of close exposure to someone with a moderately severe cold. The median duration of the rhinovirus-associated cold episodes was estimated to be around 11 days; with specific nasal IgA antibody response appearring withint about 24 hours. However, this immune response does not become significant until about 1 week after initial infection and only reach a maximal response at 5 weeks. Therefore, although infectivity does decrease over time, it remains moderately contagious in the first week or so; and there is little truth in saying that the common cold is no longer infectious by the time symptoms appear.
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References:- 1. Ledingham JGG, Warrell DA. Concise Oxford Textbook of Medicine. Oxford University Press 2. Elliott T, Hastings M, Desselberger U. Lecture Notes on Medical Microbiology. Blackwell Science 3. Callow KA, Parry HF, Sergeant M, Tyrrell DA. The time course of the immune response to experimental coronavirus infection of man. Epidemiol Infect. 1990 Oct;105(2):435-46. 4. Barclay WS, al-Nakib W, Higgins PG, Tyrrell DA. The time course of the humoral immune response to rhinovirus infection. Epidemiol Infect. 1989 Dec;103(3):659-69.
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