Virus
The causal agent, EEE, 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 35% 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.
Read more about this topic: Eastern Equine Encephalitis Virus
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