Eastern Equine Encephalitis is a mosquito
borne Alphavirus which produces a deadly disease in horses and
can also infect humans. It is closely related to Western
and Venezuelan Equine Encephalitis, which are also Togaviruses
of the Alphavirus genus.
- Incubation: 3 - 7 days
- Epidemiology: EEE virus is prevalent
in North, Central, and South America, as well as the Caribbean.
It is maintained in swamps where its reservoir population of
wild birds and its vector population of the mosquito Culiseta
melandra reside. Its natural hosts are humans and horses,
and it produces periodic epidemics within both species.
- Symptoms and Outcomes: Most
EEE virus infections of humans are subclinical or produce only
a low-grade fever. However, in some cases, this fever may
be followed by the prodromic symptoms of encephalitis.
The typical course includes increasing drowsiness, neck rigidity,
confusion, paralysis, convulsions and coma. EEE is fatal
in more than 20% of cases which develop encephalitis. Survivors
have permanent sequelae including mental retardation, epilepsy,
paralysis, deafness, and blindness.
- Pathology and Pathogenesis: EEE
virus enters the bloodstream via the saliva of an infected female
mosquito. Viral replication then occurs in the monocytes
leading to the viremic phase of infection. The virus can
also infect the capillary endothelial cells to enter the CNS.
This leads to neuronal necrosis with neuronophagia.
- Prevention and Management: The easiest
way to control EEE is to reduce exposure. This can be accomplished
by reducing the size and number of mosquito breeding sites through
public education measures. Additionally, the yearly vaccination
of horses reduces the chance of host amplification. A human
vaccination also exists and is given to at-risk lab workers,
but the low number of EEE infections does not warrant its universal
use. Treatment of EEE is largely symptomatic.
EEE virus is transmitted from birds to mosquitoes to humans and
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