Eastern equine encephalitis
| Eastern equine encephalomyelitis | |
|---|---|
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| Colourised TEM micrograph of a mosquito salivary gland. The red dots are coloured red. (83,900x magnification) | |
| Virus classification | |
| Group: | Group IV ((+)ssRNA) |
| Family: | Togaviridae |
| Genus: | Alphavirus |
| Species: | Eastern equine encephalitis virus |
| Eastern equine encephalitis virus | |
|---|---|
| Classification and external resources | |
| Specialty | infectious disease |
| ICD-10 | A83.2 |
| ICD-9-CM | 062.2 |
| MeSH | D020242 |
Eastern equine encephalitis virus (EEE), commonly called Triple E or, sleeping sickness (not to be confused with Trypanosomiasis) is a zoonotic alphavirus and arbovirus present in North, Central and South America and the Caribbean. EEE was first recognized in Massachusetts, United States in 1831 when 75 horses died mysteriously of viral encephalitis.
Epizootics in horses have continued to occur regularly in the United States. EEE is found today in the eastern part of the country and is often associated with coastal plains.
EEEV is closely related to Venezuelan equine encephalitis virus and Western equine encephalitis virus.
The causative agent, later identified as a togavirus was first isolated from infected horse brains in 1933. In 1938, the first confirmed human cases were identified when thirty children died of encephalitis in the northeastern United States. These cases coincided with outbreaks in horses in the same regions. The fatality rate in humans is 33% and there is currently no cure for human infections. This virus has two distinct antigenic variants, the more pathogenic North American (NA) and the less pathogenic South American (SA).
These two clades may actually be distinct viruses. The NA strains appear to be monotypic with a mutation rate of 2.7 × 10−4 substitutions/site/year (s/s/y). It appears to have diverged from the SA strains 922 to 4,856 years ago. The SA strains are divided into two main clades and a third smaller one. The two main clades diverged between 577 and 2,927 years ago. The mutation rate in the genome has been estimated to be 1.2 × 10−4 s/s/y.
EEE is capable of infecting a wide range of animals including mammals, birds, reptiles and amphibians. The virus is maintained in nature through a bird—mosquito cycle. There are two mosquito species primarily involved in this portion of the cycle, they are Culiseta melanura and Cs. morsitans. These mosquitoes feed on the blood of birds. The amount of virus found in nature increases throughout the summer as more birds and more mosquitoes become infected.
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