View source for Saint Louis encephalitis

{{Short description|Mosquito-borne viral disease mainly in the US}}
{{More citations needed|date=May 2023}}
{{Virusbox
| image = St. Louis Encephalitis (SLE) virus EM PHIL 1871 lores.JPG
| image_alt = Electron micrograph of "Saint Louis encephalitis virus" seen in a mosquito salivary gland
| image_caption = [[Electron micrograph]] of ''Saint Louis encephalitis virus'' seen in a [[mosquito]] [[salivary gland]]
| parent = Flavivirus
| species = Saint Louis encephalitis virus
| synonyms =
* ''St. Louis encephalitis virus''<ref name="2017.001G">{{cite web |last1=Siddell |first1=Stuart |title=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. |url=https://ictv.global/ictv/proposals/2017.001G.A.v2.43spren.zip |website=International Committee on Taxonomy of Viruses (ICTV) |access-date=29 April 2019 |language=en |format=ZIP |date=April 2017}}</ref>
* ''St. Louis virus''<ref>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, p226 https://ictv.global/ictv/proposals/ICTV%205th%20Report.pdf</ref>
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'''Saint Louis encephalitis''' is a disease caused by the [[mosquito]]-borne '''Saint Louis encephalitis virus'''.  Saint Louis encephalitis virus is related to [[Japanese encephalitis virus]] and is a member of the family ''[[Flaviviridae]]''. This disease mainly affects the United States, including Hawaii.<ref name="Hotspots">{{cite journal |last1=Mavian |first1=Carla |last2=Dulcey |first2=Melissa |last3=Munoz |first3=Olga |last4=Salemi |first4=Marco |last5=Vittor |first5=Amy |last6=Capua |first6=Ilaria |title=Islands as Hotspots for Emerging Mosquito-Borne Viruses: A One-Health Perspective |journal=Viruses |date=25 December 2018 |volume=11 |issue=1 |pages=11 |doi=10.3390/v11010011 |pmid=30585228 |pmc=6356932 |doi-access=free }}</ref> Occasional cases have been reported from Canada, Mexico and the Caribbean, including the [[Greater Antilles]], Trinidad and Tobago, and Jamaica.<ref name="Hotspots"/>

==Signs and symptoms==
The majority of infections result in mild illness, including [[fever]] and [[headache]]. When infection is more severe the person may experience headache, high fever, neck stiffness, [[stupor]], disorientation, [[coma]], tremors, occasional convulsions and spastic [[paralysis]]. Fatality ranges from {{nowrap|3–30%}}. Elderly people are more likely to have a fatal infection.{{citation needed|date=September 2022}}

==Transmission==
[[Mosquito]]es, primarily from the genus ''[[Culex]]'', become infected by feeding on [[bird]]s infected with the Saint Louis encephalitis virus. The most common vector of this disease within the genus ''Culex'' is ''[[Culex pipiens]]'', also known as the common house mosquito.<ref>{{cite web|title=Saint Louis Encephalitis|url=https://www.cdc.gov/sle/technical/fact.html|publisher=Centers for Disease Control and Prevention|access-date=July 14, 2017|date=November 20, 2009}}</ref> 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 a [[human]] has been infected with the virus it is not transmissible from that individual to other humans.{{citation needed|date=September 2022}}

==Genetics==
Five evolutionary genetic studies of SLE virus have been published of which four<ref>{{cite journal |vauthors=Kramer LD, Presser SB, Hardy JL, Jackson AO |title=Genotypic and phenotypic variation of selected Saint Louis encephalitis viral strains isolated in California |journal=Am. J. Trop. Med. Hyg. |volume=57 |issue=2 |pages=222–9 |year=1997 |pmid=9288820 |doi=10.4269/ajtmh.1997.57.222 }}</ref><ref>{{cite journal |vauthors=Kramer LD, Chandler LJ |title=Phylogenetic analysis of the envelope gene of St. Louis encephalitis virus |journal=Arch. Virol. |volume=146 |issue=12 |pages=2341–55 |year=2001 |pmid=11811684 |doi=10.1007/s007050170007|s2cid=24755534 }}</ref><ref>{{cite journal |vauthors=Twiddy SS, Holmes EC |title=The extent of homologous recombination in members of the genus Flavivirus |journal=J. Gen. Virol. |volume=84 |issue=Pt 2 |pages=429–40 |year=2003 |pmid=12560576 |doi=10.1099/vir.0.18660-0 |doi-access=free }}</ref><ref name=May2008JGV>{{cite journal |vauthors=May FJ, Li L, Zhang S, Guzman H, Beasley DW, Tesh RB, Higgs S, Raj P, Bueno R, Randle Y, Chandler L, Barrett AD |title=Genetic variation of St. Louis encephalitis virus |journal=J. Gen. Virol. |volume=89 |issue=Pt 8 |pages=1901–10 |year=2008 |pmid=18632961 |pmc=2696384 |doi=10.1099/vir.0.2008/000190-0 }}</ref> focused on [[phylogeny]], [[genetic variation]], and [[Genetic recombination|recombination]] dynamics by sequencing the [[Envelope (biology)|''envelope'' protein]] gene and parts of other genes.

A recent evolutionary study<ref>{{cite journal |vauthors=Baillie GJ, Kolokotronis SO, Waltari E, Maffei JG, Kramer LD, Perkins SL |title=Phylogenetic and evolutionary analyses of St. Louis encephalitis virus genomes |journal=Mol. Phylogenet. Evol. |volume=47 |issue=2 |pages=717–28 |year=2008 |pmid=18374605 |doi=10.1016/j.ympev.2008.02.015 |bibcode=2008MolPE..47..717B }}</ref> based on 23 new full [[open reading frame]] sequences (near-complete [[genomes]]) found that the [[North America]]n strains belonged to a single [[clade]]. 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 the [[effective population size]] of 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 the [[Americas]], and a split from the ancestral South American strains around 1892.<ref name="AMNH">{{cite web |title=Solving The Mystery Of St. Louis Encephalitis |url=https://www.amnh.org/research/science-news/2008/solving-the-mystery-of-st.-louis-encephalitis |publisher=American Museum of Natural History |access-date=28 July 2019 |date=30 July 2008}}</ref> Scans for natural selection showed that most [[codons]] of the SLE virus [[Open reading frame|ORF]] were evolving [[Neutral theory of molecular evolution|neutrally]] or under [[Negative selection (natural selection)|negative selection]]. Positive selection was statistically detected only at one single codon coding for [[amino acid]]s belonging to the hypothesized [[Glycosylation#N-linked glycosylation|''N''-linked]] [[glycosylation]] site of the [[Envelope (biology)|''envelope'' protein]]. Nevertheless, the latter can be due to selection ''[[in vitro]]'' (laboratory) rather than ''[[in vivo]]'' (host). In an independent study<ref name=May2008JGV/> 14 out of 106 examined ''envelope'' gene sequences were found not to contain a specific codon at position 156 coding for this glycosylation site ([[Aminoacid|Ser→Phe/Tyr]]).{{citation needed|date=September 2022}}

Another study estimated the evolutionary rate to be {{nowrap|4.1 × 10<sup>−4</sup> substitutions/site/year}} (95% confidence {{nowrap|internal 2.5-5.7 × 10<sup>−4</sup> substitutions/site/year}}).<ref name=Auguste2009>{{cite journal |vauthors=Auguste AJ, Pybus OG, Carrington CV |title=Evolution and dispersal of St. Louis encephalitis virus in the Americas |journal=Infect. Genet. Evol. |volume=9 |issue=4 |pages=709–15 |year=2009 |pmid=18708161 |doi=10.1016/j.meegid.2008.07.006 |bibcode=2009InfGE...9..709A }}</ref> The virus seems to have evolved in northern Mexico and then spread northwards with migrating birds.

==Treatment==
There are no [[vaccines]] or any other treatments specifically for Saint Louis encephalitis virus, although one study showed that early use of [[interferon alfa-2b]] may decrease the severity of complications.<ref>{{cite journal |vauthors=Rahal JJ, Anderson J, Rosenberg C, Reagan T, Thompson LL |title=Effect of interferon-alpha2b therapy on St. Louis viral meningoencephalitis: clinical and laboratory results of a pilot study |journal=J. Infect. Dis. |volume=190 |issue=6 |pages=1084–7 |year=2004 |pmid=15319857 |doi=10.1086/423325 |doi-access=free }}</ref>

==Epidemiology==
[[Image:St louis encephalitis map.PNG|thumb|300px|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|date=September 2022}}

==History==
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 of [[St. Louis]], [[Missouri]], and the neighboring [[St. Louis County, Missouri|St. Louis County]].<ref name="pmid18013846">{{cite journal |title=Encephalitis in St. Louis |journal=American Journal of Public Health and the Nation's Health |volume=23 |issue=10 |pages=1058–60 |date=October 1933  |pmid=18013846 |pmc=1558319 |doi= 10.2105/ajph.23.10.1058}}</ref><ref>Washington Post Magazine, October 8, 1933</ref>
Over 1,000 cases were reported to the local health departments and the newly constituted [[National Institutes of Health]] of the United States was appealed to for epidemiological and investigative expertise.<ref name="pmid18013860">{{cite journal |author=Bredeck JF |title=The Story of the Epidemic of Encephalitis in St. Louis |journal=American Journal of Public Health and the Nation's Health |volume=23 |issue=11 |pages=1135–40 |date=November 1933  |pmid=18013860 |pmc=1558406 |doi= 10.2105/AJPH.23.11.1135}}</ref>
The previously unknown virus that caused the epidemic was isolated by the NIH team first in monkeys and then in white mice.<ref>Edward A. Beeman: ''Charles Armstrong, M.D.: A Biography''; 2007; p. 305; [http://history.nih.gov/01Docs/historical/documents/ArmstrongBiography.pdf also online here (PDF)].</ref>

On August 8, 2001, an outbreak of this disease prompted an emergency alert in Louisiana after 63 cases were reported.<ref>'St. Louis encephalitis outbreak in Louisiana in 2001' [https://pubmed.ncbi.nlm.nih.gov/12517026/ PMID 12517026].</ref>

==References==
{{Reflist}}

== External links ==
{{Portal|Biology|Medicine}}
* United States [[Centers for Disease Control and Prevention]]. [https://www.cdc.gov/sle/ Saint Louis encephalitis].
* {{EMedicine|article|233710|St. Louis Encephalitis}}
* [http://www.encephalitis.info The Encephalitis Society - A Global resource on Encephalitis]
* {{cite web |title=''St. Louis encephalitis virus'' |work=NCBI Taxonomy Browser |url=https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Info&id=11080 |id=11080}}

{{Zoonotic viral diseases}}
{{Medical resources
|  DiseasesDB     = 29860
|  ICD11          = {{ICD11|1C86}}
|  ICD10          = {{ICD10|A|83|3|a|80}}
|  ICD9           = {{ICD9|062.3}}
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|  MeshID         = D004674
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{{DEFAULTSORT:Saint Louis encephalitis}}
[[Category:Viral encephalitis]]
[[Category:Insect-borne diseases]]