129: Western Equine Encephalitis

Classification: ICD-9 062; ICD-10 A83.1

Syndromes and synonyms: None.

Agents: Western equine encephalitis virus (WEEV), an enveloped, spherical, single-stranded positive-sense RNA virus, genus Alphavirus in the family Togaviridae. WEEV is believed to have descended from an ancestral recombinant derived from eastern equine encephalitis virus and Sindbis virus.

Reservoir: Principally birds, secondarily rabbits, poultry.

Vector: Mosquitoes. In North America, the primary vector of WEEV for the enzootic cycle is Culex tarsalis. WEEV is transmitted to humans and horses by bridging mosquitoes (e.g. Ochlerotatus melanimon and Aedes species).

Transmission: Mosquito bite. There is no direct person-to-person transmission.

Cycle: Mosquito to reservoir animal to mosquito. There is an enzootic cycle, mainly between C. taralsis

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