Rhinovirus
From Wikipedia, the free encyclopedia
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Human rhinovirus A (HRV-A) |
Rhinovirus (from the Greek rhin-, which means "nose") is a genus of the Picornaviridae family of viruses. Rhinoviruses are the most common viral infective agents in humans, and a causative agent of the common cold. There are over 105 serologic virus types that cause cold symptoms, and rhinoviruses are responsible for approximately 50% of all cases.
Rhinoviruses have single-stranded positive sense RNA genomes of between 7.2 and 8.5kb 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 end. This is the same for all picornaviruses. The viral particles themselves are not enveloped and are icosahedral in structure.
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[edit] Structure
Rhinoviruses are composed of a capsid, that contains four viral proteins VP1, VP2, VP3 and VP4.[1][2] 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 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 defense against infection with the epitopes lying on the exterior regions of VP1-VP3.
[edit] Transmission and epidemiology
Rhinoviruses have two main modes of transmission: In the past it was obvious that these viruses were transmitted directly from person-to-person via aerosols of respiratory droplets. However, now they are known to be transmitted indirectly via respiratory droplets that are deposited on the hands and then transported by fingers to the nose or eyes.
Rhinoviruses occur worldwide causing disease especially at schools for example which enhance transmission during fall and winter. They show symptoms such as fever, cough, and nasal congestion. The frequency of colds is high in childhood and decreases during adulthood most probably because of the possession of immunity.
[edit] Pathogenesis
Most people are infected with a rhinovirus. The common cold occurs only when the immune system is weakened. The most common reason for this is stress. The primary route of entry for rhinoviruses is the upper respiratory tract. Afterwards, the virus binds to ICAM-1 (intracellular adhesion molecule -1) 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).
Rhinoviruses rarely cause lower respiratory tract disease probably because they grow poorly at 37°C.
[edit] Novel antiviral drugs
Interferon-alpha used intranasally was shown to be protective to rhinovirus infections. However, volunteers treated with this drug experienced some side effects, such as nasal bleeding, and resistance was also developing toward the drug. Hence, all research put into this drug was ceased.
Pleconaril, is a bioavailable antiviral drug that is taken orally for treating infections caused by picornaviruses.[3] This drug acts by binding to a hydrophobic pocket in VP1 and stabilizes the protein capsid to such an extent that the virus cannot release its RNA genome into the target cell. When tested in volunteers, during the clinical trials, this drug caused a significant decrease in mucus secretions and illness-associated symptoms. Pleconaril is not currently available for treatment of rhinoviral infections, as its efficacy in treating these infections is under further evaluation.[4]
[edit] Vaccine
There are no vaccines against this virus.
[edit] References
- ^ Rossmann M, Arnold E, Erickson J, Frankenberger E, Griffith J, Hecht H, Johnson J, Kamer G, Luo M, Mosser A (1985). "Structure of a human common cold virus and functional relationship to other picornaviruses.". Nature 317 (6033): 145-53. PMID 2993920.
- ^ Smith T, Kremer M, Luo M, Vriend G, Arnold E, Kamer G, Rossmann M, McKinlay M, Diana G, Otto M (1986). "The site of attachment in human rhinovirus 14 for antiviral agents that inhibit uncoating.". Science 233 (4770): 1286-93. PMID 3018924.
- ^ Pevear D, Tull T, Seipel M, Groarke J (1999). "Activity of pleconaril against enteroviruses.". Antimicrob Agents Chemother 43 (9): 2109-15. PMID 10471549.
- ^ Fleischer R, Laessig K (2003). "Safety and efficacy evaluation of pleconaril for treatment of the common cold.". Clin Infect Dis 37 (12): 1722. PMID 14689362.
- Smith, T. J., Chase, E. S., Schmidt, T. J., Olson, N. H. & Baker, T. S. (1996). Neutralizing antibody to human rhinovirus 14 penetrates the receptor-binding canyon. Nature 383, 350-354.
- Abraham, G. & Colonno, R. J. (1984). Many rhinovirus serotypes share the same cellular receptor. J. Virol. 51: 340-345.
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