Mosquito-borne viral disease mainly in the US
Medical condition
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.
[3]
Occasional cases have been reported from Canada, Mexico and the Caribbean, including the
Greater Antilles
, Trinidad and Tobago, and Jamaica.
[3]
Signs and symptoms
[
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]
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
3?30%
. Elderly people are more likely to have a fatal infection.
[
citation needed
]
Transmission
[
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]
Mosquitoes
, primarily from the genus
Culex
, become infected by feeding on
birds
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.
[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 a
human
has 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 on
phylogeny
,
genetic variation
, and
recombination
dynamics by sequencing the
envelope
protein
gene and parts of other genes.
A recent evolutionary study
[9]
based on 23 new full
open reading frame
sequences (near-complete
genomes
) found that the
North American
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.
[10]
Scans for natural selection showed that most
codons
of the SLE virus
ORF
were evolving
neutrally
or under
negative selection
. Positive selection was statistically detected only at one single codon coding for
amino acids
belonging to the hypothesized
N
-linked
glycosylation
site of the
envelope
protein
. Nevertheless, the latter can be due to selection
in vitro
(laboratory) rather than
in vivo
(host). In an independent study
[8]
14 out of 106 examined
envelope
gene 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 be
4.1 × 10
?4
substitutions/site/year
(95% confidence
internal 2.5-5.7 × 10
?4
substitutions/site/year
).
[11]
The virus seems to have evolved in northern Mexico and then spread northwards with migrating birds.
Treatment
[
edit
]
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.
[12]
Epidemiology
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]
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 of
St. Louis
,
Missouri
, and the neighboring
St. Louis County
.
[13]
[14]
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.
[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
[
edit
]
- ^
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)
. Retrieved
29 April
2019
.
- ^
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
- ^
a
b
Mavian, 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
.
PMC
6356932
.
PMID
30585228
.
- ^
"Saint Louis Encephalitis"
. Centers for Disease Control and Prevention. November 20, 2009
. Retrieved
July 14,
2017
.
- ^
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
.
PMID
9288820
.
- ^
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
.
PMID
11811684
.
S2CID
24755534
.
- ^
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
.
PMID
12560576
.
- ^
a
b
May 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
.
PMC
2696384
.
PMID
18632961
.
- ^
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.
doi
:
10.1016/j.ympev.2008.02.015
.
PMID
18374605
.
- ^
"Solving The Mystery Of St. Louis Encephalitis"
. American Museum of Natural History. 30 July 2008
. Retrieved
28 July
2019
.
- ^
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.
doi
:
10.1016/j.meegid.2008.07.006
.
PMID
18708161
.
- ^
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
.
PMID
15319857
.
- ^
"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
.
PMC
1558319
.
PMID
18013846
.
- ^
Washington Post Magazine, October 8, 1933
- ^
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
.
PMC
1558406
.
PMID
18013860
.
- ^
Edward A. Beeman:
Charles Armstrong, M.D.: A Biography
; 2007; p. 305;
also online here (PDF)
.
External links
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St. Louis encephalitis virus
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