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Saint Louis encephalitis

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Saint Louis encephalitis virus
Electron micrograph of "Saint Louis encephalitis virus" seen in a mosquito salivary gland
Electron micrographofSaint Louis encephalitis virusseen in amosquitosalivary gland
Virus classificationEdit this classification
(unranked): Virus
Realm: Riboviria
Kingdom: Orthornavirae
Phylum: Kitrinoviricota
Class: Flasuviricetes
Order: Amarillovirales
Family: Flaviviridae
Genus: Flavivirus
Species:
Saint Louis encephalitis virus
Synonyms
  • St. Louis encephalitis virus[1]
  • St. Louis virus[2]
Saint Louis encephalitis
SpecialtyInfectious diseasesEdit this on Wikidata

Saint Louis encephalitisis a disease caused by themosquito-borneSaint Louis encephalitis virus.Saint Louis encephalitis virus is related toJapanese encephalitis virusand is a member of the familyFlaviviridae.This disease mainly affects the United States, including Hawaii.[3]Occasional cases have been reported from Canada, Mexico and the Caribbean, including theGreater Antilles,Trinidad and Tobago, and Jamaica.[3]

Signs and symptoms

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The majority of infections result in mild illness, includingfeverandheadache.When infection is more severe the person may experience headache, high fever, neck stiffness,stupor,disorientation,coma,tremors, occasional convulsions and spasticparalysis.Fatality ranges from3–30%.Elderly people are more likely to have a fatal infection.[citation needed]

Transmission

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Mosquitoes,primarily from the genusCulex,become infected by feeding onbirdsinfected with the Saint Louis encephalitis virus. The most common vector of this disease within the genusCulexisCulex pipiens,also known as the common house mosquito.[4]Infected mosquitoes then transmit the Saint Louis encephalitis virus to humans and animals during the feeding process. The Saint Louis encephalitis virus grows both in the infected mosquito and the infected bird, but does not make either one sick. Only infected mosquitoes can transmit Saint Louis encephalitis virus. Once ahumanhas been infected with the virus it is not transmissible from that individual to other humans.[citation needed]

Genetics

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Five evolutionary genetic studies of SLE virus have been published of which four[5][6][7][8]focused onphylogeny,genetic variation,andrecombinationdynamics by sequencing theenvelopeproteingene and parts of other genes.

A recent evolutionary study[9]based on 23 new fullopen reading framesequences (near-completegenomes) found that theNorth Americanstrains belonged to a singleclade.Strains were isolated at different points in time (from 1933 to 2001) which allowed for the estimation of divergence times of SLE virus clades and the overall evolutionary rate. Furthermore, this study found an increase in theeffective population sizeof the SLE virus around the end of the 19th century that corresponds to the split of the latest North American clade, suggesting a northwards colonization of SLE virus in theAmericas,and a split from the ancestral South American strains around 1892.[10]Scans for natural selection showed that mostcodonsof the SLE virusORFwere evolvingneutrallyor undernegative selection.Positive selection was statistically detected only at one single codon coding foramino acidsbelonging to the hypothesizedN-linkedglycosylationsite of theenvelopeprotein.Nevertheless, the latter can be due to selectionin vitro(laboratory) rather thanin vivo(host). In an independent study[8]14 out of 106 examinedenvelopegene sequences were found not to contain a specific codon at position 156 coding for this glycosylation site (Ser→Phe/Tyr).[citation needed]

Another study estimated the evolutionary rate to be4.1 × 10−4substitutions/site/year(95% confidenceinternal 2.5-5.7 × 10−4substitutions/site/year).[11]The virus seems to have evolved in northern Mexico and then spread northwards with migrating birds.

Treatment

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There are novaccinesor any other treatments specifically for Saint Louis encephalitis virus, although one study showed that early use ofinterferon alfa-2bmay decrease the severity of complications.[12]

Epidemiology

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Human incidence of Saint Louis encephalitis in the United States, 1964–1998.

In the United States an average of 128 cases of Saint Louis encephalitis are recorded annually. In temperate areas of the United States, Saint Louis encephalitis cases occur primarily in the late summer or early fall. In the southern United States where the climate is milder Saint Louis encephalitis can occur year-round.[citation needed]

History

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The name of the virus goes back to 1933 when within five weeks in autumn an encephalitis epidemic of explosive proportions broke out in the vicinity ofSt. Louis,Missouri,and the neighboringSt. Louis County.[13][14] Over 1,000 cases were reported to the local health departments and the newly constitutedNational Institutes of Healthof the United States was appealed to for epidemiological and investigative expertise.[15] The previously unknown virus that caused the epidemic was isolated by the NIH team first in monkeys and then in white mice.[16]

On September 11, 2001, an outbreak of this disease prompted an emergency alert in Louisiana after 50 cases were reported.

References

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  1. ^Siddell, Stuart (April 2017)."Change the names of 43 virus species to accord with ICVCN Code, Section 3-II, Rule 3.13 regarding the use of ligatures, diacritical marks, punctuation marks (excluding hyphens), subscripts, superscripts, oblique bars and non-Latin letters in taxon names"(ZIP).International Committee on Taxonomy of Viruses (ICTV).Retrieved29 April2019.
  2. ^ICTV 5th Report Francki, R. I. B., Fauquet, C. M., Knudson, D. L. & Brown, F. (eds)(1991). Classification and nomenclature of viruses. Fifthreport of the International Committee on Taxonomy of Viruses. Archives of Virology Supplementum 2, p226https://ictv.global/ictv/proposals/ICTV%205th%20Report.pdf
  3. ^abMavian, Carla; Dulcey, Melissa; Munoz, Olga; Salemi, Marco; Vittor, Amy; Capua, Ilaria (25 December 2018)."Islands as Hotspots for Emerging Mosquito-Borne Viruses: A One-Health Perspective".Viruses.11(1): 11.doi:10.3390/v11010011.PMC6356932.PMID30585228.
  4. ^"Saint Louis Encephalitis".Centers for Disease Control and Prevention. November 20, 2009.RetrievedJuly 14,2017.
  5. ^Kramer LD, Presser SB, Hardy JL, Jackson AO (1997). "Genotypic and phenotypic variation of selected Saint Louis encephalitis viral strains isolated in California".Am. J. Trop. Med. Hyg.57(2): 222–9.doi:10.4269/ajtmh.1997.57.222.PMID9288820.
  6. ^Kramer LD, Chandler LJ (2001). "Phylogenetic analysis of the envelope gene of St. Louis encephalitis virus".Arch. Virol.146(12): 2341–55.doi:10.1007/s007050170007.PMID11811684.S2CID24755534.
  7. ^Twiddy SS, Holmes EC (2003)."The extent of homologous recombination in members of the genus Flavivirus".J. Gen. Virol.84(Pt 2): 429–40.doi:10.1099/vir.0.18660-0.PMID12560576.
  8. ^abMay FJ, Li L, Zhang S, Guzman H, Beasley DW, Tesh RB, Higgs S, Raj P, Bueno R, Randle Y, Chandler L, Barrett AD (2008)."Genetic variation of St. Louis encephalitis virus".J. Gen. Virol.89(Pt 8): 1901–10.doi:10.1099/vir.0.2008/000190-0.PMC2696384.PMID18632961.
  9. ^Baillie GJ, Kolokotronis SO, Waltari E, Maffei JG, Kramer LD, Perkins SL (2008). "Phylogenetic and evolutionary analyses of St. Louis encephalitis virus genomes".Mol. Phylogenet. Evol.47(2): 717–28.Bibcode:2008MolPE..47..717B.doi:10.1016/j.ympev.2008.02.015.PMID18374605.
  10. ^"Solving The Mystery Of St. Louis Encephalitis".American Museum of Natural History. 30 July 2008.Retrieved28 July2019.
  11. ^Auguste AJ, Pybus OG, Carrington CV (2009). "Evolution and dispersal of St. Louis encephalitis virus in the Americas".Infect. Genet. Evol.9(4): 709–15.Bibcode:2009InfGE...9..709A.doi:10.1016/j.meegid.2008.07.006.PMID18708161.
  12. ^Rahal JJ, Anderson J, Rosenberg C, Reagan T, Thompson LL (2004)."Effect of interferon-alpha2b therapy on St. Louis viral meningoencephalitis: clinical and laboratory results of a pilot study".J. Infect. Dis.190(6): 1084–7.doi:10.1086/423325.PMID15319857.
  13. ^"Encephalitis in St. Louis".American Journal of Public Health and the Nation's Health.23(10): 1058–60. October 1933.doi:10.2105/ajph.23.10.1058.PMC1558319.PMID18013846.
  14. ^Washington Post Magazine, October 8, 1933
  15. ^Bredeck JF (November 1933)."The Story of the Epidemic of Encephalitis in St. Louis".American Journal of Public Health and the Nation's Health.23(11): 1135–40.doi:10.2105/AJPH.23.11.1135.PMC1558406.PMID18013860.
  16. ^Edward A. Beeman:Charles Armstrong, M.D.: A Biography;2007; p. 305;also online here (PDF).
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