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Characteristic	Data
Nucleic acid	RNA
Sense	Positive-sense
Virion	Enveloped
Capsid	Spherical
Symmetry	Yes; T=4 icosahedral
Capsid monomers	240
Monomer length (diameter)	65-70 nm
Additional envelope information	80 spikes; each spike is a trimer of E1/E2 proteins
Genome shape	Linear
Genome length	11-12 kb
Nucleotide cap	Yes
Polyadenylated tail	Yes
Incubation period	4-10 days

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 is a trimer of E1/E2 proteins.

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. 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 mosquitos and avian hosts in freshwater hardwood swamps. Culiseta 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. Humans and horses are dead-end hosts for the virus, meaning there is an insufficient amount of eastern equine encephalitis virus in the blood stream to infect a mosquito. Many cases in horses are fatal. There is no known transmission between horses and humans. Recent studies have demonstrated other equine, such as mules and donkeys, and other animals, such as pigs, reptiles, amphibians, and rodents, can be infected.

Eastern equine encephalitis virus is transmitted in the following pattern:

1. Attachment of the viral E glycoprotein to host receptors mediates clathrin-mediated endocytosis of virus into the host cell.
2. Fusion of virus membrane with the host cell membrane. RNA genome is released into the cytoplasm.
3. The positive-sense ssRNA virus is translated into a polyprotein, which is cleaved into non-structural proteins necessary for RNA synthesis (replication and transcription).
4. Replication takes place in cytoplasmic viral factories at the surface of endosomes. A dsRNA genome is synthesized from the genomic ssRNA(+).
5. The dsRNA genome is transcribed thereby providing viral mRNAs (new ssRNA(+) genomes).
6. Expression of the subgenomic RNA (sgRNA) gives rise to the structural proteins.
7. Virus assembly occurs at the endoplasmic reticulum.
8. Virions bud at the endoplasmic reticulum, are transported to the Golgi apparatus, and then exit the cell via the secretory pathway.