Eastern equine encephalitis: Difference between revisions
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==Classification== | ==Classification== | ||
Eastern equine encephalitis may be classified according to location of the disease into 2 subtypes: systemic or encephalitic. Eastern equine encephalitis belongs to the Group IV positive-sense ssRNA virus within the Togaviridae family of viruses, and the genus Alphavirus. Eastern equine encephalitis is closely related to western equine encephalitis virus and Venezuelan equine encephalitis virus. | Eastern equine encephalitis may be classified according to location of the disease into 2 subtypes: systemic or encephalitic. Eastern equine encephalitis belongs to the Group IV positive-sense ssRNA virus within the [[Togaviridae]] family of viruses, and the genus [[Alphavirus]]. Eastern equine encephalitis is closely related to western equine encephalitis virus and Venezuelan equine encephalitis virus. | ||
==Pathophysiology== | ==Pathophysiology== | ||
Eastern equine encephalitis virus is usually transmitted via [[mosquito]]s to the human host. Eastern equine encephalitis virus contains [[positive-sense ssRNA virus|positive-sense]] viral [[RNA]]; this RNA has its genome directly utilized as if it were mRNA, producing a single protein which is modified by host and viral proteins to form the various proteins needed for replication. One of these includes [[RNA replicase]], which copies the viral RNA to form a double-stranded replicative form, in turn this directs the formation of new virions. Eastern equine encephalitis is made up of an [[enveloped virus|enveloped virion]] with a spherical [[capsid]]. The capsid has a T=4 [[icosahedral]] symmetry made of 240 monomers and measuring approximately 65-70nm in diameter. The envelope contains 80 spikes, each spike are [[trimer]] of E1/E2 proteins.<ref name=ViralZoneAlpha> Alphavirus. SIB Swiss Institute of Bioinformatics. http://viralzone.expasy.org/viralzone/all_by_species/625.html Accessed on March 15, 2016 </ref> | Eastern equine encephalitis virus is usually transmitted via [[mosquito]]s to the human host. Eastern equine encephalitis virus contains [[positive-sense ssRNA virus|positive-sense]] viral [[RNA]]; this RNA has its genome directly utilized as if it were mRNA, producing a single protein which is modified by host and viral proteins to form the various proteins needed for replication. One of these includes [[RNA replicase]], which copies the viral RNA to form a double-stranded replicative form, in turn this directs the formation of new virions. Eastern equine encephalitis is made up of an [[enveloped virus|enveloped virion]] with a spherical [[capsid]]. The capsid has a T=4 [[icosahedral]] symmetry made of 240 monomers and measuring approximately 65-70nm in diameter. The envelope contains 80 spikes, each spike are [[trimer]] of E1/E2 proteins.<ref name=ViralZoneAlpha> Alphavirus. SIB Swiss Institute of Bioinformatics. http://viralzone.expasy.org/viralzone/all_by_species/625.html Accessed on March 15, 2016 </ref> | ||
The genome of eastern equine encephalitis is monopartite, linear, [[positive-sense ssRNA virus|ssRNA(+)]], and approximately 11-12 kb. The genome | The genome of eastern equine encephalitis is monopartite, linear, [[positive-sense ssRNA virus|ssRNA(+)]], and approximately 11-12 kb. The genome has a [[methylated]] [[nucleotide]] cap and [[Polyadenylation|polyadenylated]] tail.<ref name=ViralZoneAlpha> Alphavirus. SIB Swiss Institute of Bioinformatics. http://viralzone.expasy.org/viralzone/all_by_species/625.html Accessed on March 15, 2016 </ref> Eastern equine encephalitis is contracted by the [[bite]] of an infected [[mosquito]], primarily ''Culiseta melanura''. The virus is maintained in a cycle between ''Culiseta melanura'' mosquitoes and avian hosts in [[freshwater]] hardwood swamps. ''C. melanura'' is not an important vector of eastern equine virus to humans because it feeds almost exclusively on birds. Transmission to humans requires mosquito species capable of creating a "bridge" between infected birds and uninfected mammals such as some ''[[Aedes]]'', ''Coquillettidia'', and ''Culex'' species. The [[incubation period]] is 4-10 days.<ref name=CDCEEE> Eastern Equine Encephalitis. CDC. http://www.cdc.gov/EasternEquineEncephalitis/index.html Accessed on March 15, 2016 </ref> | ||
Eastern equine encephalitis virus is transmitted in the following pattern:<ref name=ViralZoneAlpha> Alphavirus. SIB Swiss Institute of Bioinformatics. http://viralzone.expasy.org/viralzone/all_by_species/625.html Accessed on March 15, 2016 </ref> | Eastern equine encephalitis virus is transmitted in the following pattern:<ref name=ViralZoneAlpha> Alphavirus. SIB Swiss Institute of Bioinformatics. http://viralzone.expasy.org/viralzone/all_by_species/625.html Accessed on March 15, 2016 </ref> | ||
#Attachment of the viral E [[glycoprotein]] to host receptors mediates [[clathrin|clathrin-mediated]] [[endocytosis]] of virus into the host cell. | |||
#Fusion of [[biological membrane|virus membrane]] with the host [[cell membrane]]. RNA genome is released into the [[cytoplasm]]. | |||
#The [[positive-sense ssRNA virus]] is [[translate]]d into a [[polyprotein]], which is cleaved into non-structural proteins necessary for RNA synthesis ([[replication]] and [[transcription]]). | |||
#[[Replication]] takes place in [[cytoplasm]]ic viral factories at the surface of [[endosome]]s. A [[dsRNA]] [[genome]] is synthesized from the genomic ssRNA(+). | |||
#The [[dsRNA]] [[genome]] is [[transcribed]] thereby providing viral [[mRNA]]s (new ssRNA(+) genomes). | |||
#Expression of the subgenomic RNA (sgRNA) gives rise to the structural proteins. | |||
#Virus assembly occurs at the [[endoplasmic reticulum]]. | |||
#[[Virion]]s bud at the [[endoplasmic reticulum]], are transported to the [[Golgi apparatus]], and then exit the cell via the [[secretory pathway]]. | |||
==Causes== | ==Causes== | ||
Revision as of 14:36, 15 March 2016
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Anthony Gallo, B.S. [2]
Synonyms and keywords: EEE; Triple E; EEEV
Overview
Historical Perspective
In 1831, eastern equine encephalitis virus was first reported in Massachusetts, USA following the sudden death of 75 horses, which died mysteriously of viral encephalitis. In 1938, the earliest evidence of eastern equine encephalitis virus activity in Canada was reported in the Ontario cities of St. George and St. Catharines.[1][2]
Classification
Eastern equine encephalitis may be classified according to location of the disease into 2 subtypes: systemic or encephalitic. Eastern equine encephalitis belongs to the Group IV positive-sense ssRNA virus within the Togaviridae family of viruses, and the genus Alphavirus. Eastern equine encephalitis is closely related to western equine encephalitis virus and Venezuelan equine encephalitis virus.
Pathophysiology
Eastern equine encephalitis virus is usually transmitted via mosquitos to the human host. Eastern equine encephalitis virus contains positive-sense viral RNA; this RNA has its genome directly utilized as if it were mRNA, producing a single protein which is modified by host and viral proteins to form the various proteins needed for replication. One of these includes RNA replicase, which copies the viral RNA to form a double-stranded replicative form, in turn this directs the formation of new virions. Eastern equine encephalitis is made up of an enveloped virion with a spherical capsid. The capsid has a T=4 icosahedral symmetry made of 240 monomers and measuring approximately 65-70nm in diameter. The envelope contains 80 spikes, each spike are trimer of E1/E2 proteins.[3]
The genome of eastern equine encephalitis is monopartite, linear, ssRNA(+), and approximately 11-12 kb. The genome has a methylated nucleotide cap and polyadenylated tail.[3] Eastern equine encephalitis is contracted by the bite of an infected mosquito, primarily Culiseta melanura. The virus is maintained in a cycle between Culiseta melanura mosquitoes and avian hosts in freshwater hardwood swamps. C. melanura is not an important vector of eastern equine virus to humans because it feeds almost exclusively on birds. Transmission to humans requires mosquito species capable of creating a "bridge" between infected birds and uninfected mammals such as some Aedes, Coquillettidia, and Culex species. The incubation period is 4-10 days.[4]
Eastern equine encephalitis virus is transmitted in the following pattern:[3]
- Attachment of the viral E glycoprotein to host receptors mediates clathrin-mediated endocytosis of virus into the host cell.
- Fusion of virus membrane with the host cell membrane. RNA genome is released into the cytoplasm.
- The positive-sense ssRNA virus is translated into a polyprotein, which is cleaved into non-structural proteins necessary for RNA synthesis (replication and transcription).
- Replication takes place in cytoplasmic viral factories at the surface of endosomes. A dsRNA genome is synthesized from the genomic ssRNA(+).
- The dsRNA genome is transcribed thereby providing viral mRNAs (new ssRNA(+) genomes).
- Expression of the subgenomic RNA (sgRNA) gives rise to the structural proteins.
- Virus assembly occurs at the endoplasmic reticulum.
- Virions bud at the endoplasmic reticulum, are transported to the Golgi apparatus, and then exit the cell via the secretory pathway.
Causes
Differentiating Eastern Equine Encephalitis from Other Diseases
Epidemiology and Demographics
Incidence
Age
Risk Factors
Natural History, Complications, and Prognosis
Natural History
Complications
Prognosis
Diagnosis
History and Symptoms
Physical Examination
Laboratory Findings
Treatment
Medical Therapy
Surgery
Prevention
References
- ↑ Schofield F, Labzoffsky N. Report on cases of suspected encephalomyelitis occurring in the vicinity of St. George. Rep Ont Dept Agric OVC. 193829:25-29.
- ↑ Carman PS, Artsob H, Emery S, Maxie MG, Pooley D, Barker IK; et al. (1995). "Eastern equine encephalitis in a horse from southwestern Ontario". Can Vet J. 36 (3): 170–2. PMC 1686920. PMID 7757923.
- ↑ 3.0 3.1 3.2 Alphavirus. SIB Swiss Institute of Bioinformatics. http://viralzone.expasy.org/viralzone/all_by_species/625.html Accessed on March 15, 2016
- ↑ Eastern Equine Encephalitis. CDC. http://www.cdc.gov/EasternEquineEncephalitis/index.html Accessed on March 15, 2016