Smallpox causes: Difference between revisions
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==Tropism== | ==Tropism== | ||
Little is known about the mechanism responsible for host species tropism of smallpox virus. The virus is known to bind mammalian cells unspecifically. There appears to be no particular extracellular receptors involved in viral internalization and initial transcription. However, intracellular availability of trans-acting factors and capacity to block host cell antiviral response, such as interferon pathway, are though to be important intracellular factors determining viral tropism. The overall immune response by the host towards the virus will be the key determinant of the outcome of the infection and the potential transmission to other hosts. | Little is known about the mechanism responsible for host species [[tropism]] of [[smallpox virus]]. The [[virus]] is known to bind mammalian cells unspecifically. There appears to be no particular extracellular [[receptors]] involved in [[viral]] internalization and initial [[transcription]]. However, [[intracellular]] availability of [[trans-acting factors]] and [[viral]] capacity to block host [[cell]] s antiviral response, such as the [[interferon]] pathway, are though to be important [[intracellular]] factors determining [[viral tropism]]. The overall [[immune response]] by the host towards the [[virus]] will be the key determinant of the [[outcome]] of the [[infection]] and the potential [[transmission]] to other hosts.<ref name="McFadden2005">{{cite journal|last1=McFadden|first1=Grant|title=Poxvirus tropism|journal=Nature Reviews Microbiology|volume=3|issue=3|year=2005|pages=201–213|issn=1740-1526|doi=10.1038/nrmicro1099}}</ref> | ||
==Natural reservoir== | ==Natural reservoir== | ||
Revision as of 18:29, 9 July 2014
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]
Overview
Smallpox is caused by the variola virus.
Taxonomy
Viruses; dsDNA; Poxviridae; Chordopoxvirinae; Orthopoxvirus; Variola vera
Biology
Variola virus is a orthopoxvirus, from the family Poxviridae, the largest viruses to infect humans. It is a 200-400 nm dsDNA virus, lacking icosahedral symmetry. The other viruses of the family Poxviridae include:[1]
The viral structure includes:[2][3][4]
- Outer membrane
- 2 lateral bodies
- 1 dsDNA molecule in its core containing 186,999 base pairs
Variola virus genes are similar to the ones of vaccinia virus. Since there is cross-protection between poxviruses, it was possible to use the second as a vaccine for smallpox virus.[5]
There are 2 forms of variola virus:
- Variola major
- Variola minor
Both strains of the virus share a large amount of genome, yet they differ clinically. This leads to the assumption that the difference in virulence resides in alternate gene expression.[1][6]
Poxviruses survive in cold and dry environments being able to survive in the aerosol form, and are killed by hospital disinfectants and UV light.[1][6][7][8]
Unlike other DNA viruses, poxviruses replicate within the cytoplasm of the host cell. In order to replicate, poxviruses produce a variety of specialized proteins not produced by other DNA viruses, the most important of which is a viral-associated DNA-dependent RNA polymerase.
Origin
Tropism
Little is known about the mechanism responsible for host species tropism of smallpox virus. The virus is known to bind mammalian cells unspecifically. There appears to be no particular extracellular receptors involved in viral internalization and initial transcription. However, intracellular availability of trans-acting factors and viral capacity to block host cell s antiviral response, such as the interferon pathway, are though to be important intracellular factors determining viral tropism. The overall immune response by the host towards the virus will be the key determinant of the outcome of the infection and the potential transmission to other hosts.[9]
Natural reservoir
Humans are the only natural reservoir of smallpox virus.[10]
References
- ↑ 1.0 1.1 1.2 Moore, Zack S; Seward, Jane F; Lane, J Michael (2006). "Smallpox". The Lancet. 367 (9508): 425–435. doi:10.1016/S0140-6736(06)68143-9. ISSN 0140-6736.
- ↑ Fields, Bernard (2007). Fields virology. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins. ISBN 0781760607.
- ↑ Massung RF, Liu LI, Qi J, Knight JC, Yuran TE, Kerlavage AR; et al. (1994). "Analysis of the complete genome of smallpox variola major virus strain Bangladesh-1975". Virology. 201 (2): 215–40. doi:10.1006/viro.1994.1288. PMID 8184534.
- ↑ Massung RF, Loparev VN, Knight JC, Totmenin AV, Chizhikov VE, Parsons JM; et al. (1996). "Terminal region sequence variations in variola virus DNA". Virology. 221 (2): 291–300. doi:10.1006/viro.1996.0378. PMID 8661439.
- ↑ Shchelkunov, Sergei N.; Resenchuk, Sergei M.; Totmenin, Alexei V.; Blinov, Vladimir M.; Marennikova, Svetlana S.; Sandakhchiev, Lev S. (1993). "Comparison of the genetic maps of variola and vaccinia viruses". FEBS Letters. 327 (3): 321–324. doi:10.1016/0014-5793(93)81013-P. ISSN 0014-5793.
- ↑ 6.0 6.1 "Smallpox and its Eradication" (PDF).
- ↑ Thomas G (1974). "Air sampling of smallpox virus". J Hyg (Lond). 73 (1): 1–7. PMC 2130554. PMID 4371586.
- ↑ HARPER GJ (1961). "Airborne micro-organisms: survival tests with four viruses". J Hyg (Lond). 59: 479–86. PMC 2134455. PMID 13904777.
- ↑ McFadden, Grant (2005). "Poxvirus tropism". Nature Reviews Microbiology. 3 (3): 201–213. doi:10.1038/nrmicro1099. ISSN 1740-1526.
- ↑ "Smallpox disease overview".