Rhinovirus

Host Defence
Take a look at the funny video that i have put up to for further understanding on this virus.



Rhinovirus transmitted by aerosol or direct contact. The primary site of inoculation is the nasal and conjunctiva may be involved to a lesser extent. Rhinovirus attaches to respiratory epithelium and spreads locally.





The natural response of the human defense system to injury involves ICAM-1, which aids the binding between endothelial cells and leukocytes. Rhinovirus takes advantage of the ICAM-1 by using it as a receptor for attachment. In addition, Rhinovirus uses ICAM-1 for subsequent viral uncoating during cell invasion. Some Rhinovirus serotypes also up-regulate ICAM-1 expression on human epithelial cells to increase susceptibility to infection.



The optimal temperature for Rhinovirus replication is 33-35°C. Rhinovirus does not efficiently replicate at body temperature. This may explain why Rhinovirus replicates well in the nasal passages and upper tracheobronchial tree but less well in the lower respiratory tract. The incubation period is approximately 2-3 days. Viremia is uncommon.



Rhinovirus is shed in large amounts, with as many as 1 million infectious virions present per mL of nasal washings. Viral shedding can occur a few days before cold symptoms are recognized by the patient, peaks on days 2-7 of the illness, and may last as long as 3-4 weeks.



A local inflammatory response to the virus in the respiratory tract can lead to nasal discharge, nasal congestion, sneezing, and throat irritation. Damage to the nasal epithelium does not occur, and inflammation is mediated by the production of cytokines and other mediators.



Histamine concentrations in nasal secretions do not increase. By days 3-5 of the illness, nasal discharge can become mucopurulent from polymorphonuclear leukocytes that have migrated to the infection site in response to chemoattractants. Nasal mucociliary transport is markedly reduced during the illness and may be impaired for weeks. Both secretory immunoglobulin A and serum antibodies are involved in resolving the illness and protecting from reinfection.



Coronaviruses, reinfections with parainfluenza, and respiratory syncytial virus (RSV) are the most important of many other viruses that can cause common colds. Other viruses can also cause common colds but are more likely to cause acute nasopharyngitis and more severe respiratory infections.



Mycoplasma pneumoniae can occasionally present with common cold symptoms before developing into more extensive respiratory disease. Abnormalities on CT scan findings (mucosal thickening) are present in adults with common colds that resolve over 1-2 weeks without antibiotic therapy.