Eastern/Western Equine Encephalomyelitis (EEE/WEE)

Disease Overview

Eastern Equine Encephalomyelitis (EEE) and Western Equine Encephalomyelitis (WEE), sometimes called “sleeping sickness,” are caused by viruses that attack the brain and spinal cord. Birds and rodents are the primary reservoirs, and the diseases are spread by mosquitos. Unvaccinated horses are particularly susceptible to EEE and WEE and often serve as sentinels of the diseases, which also affect humans. EEE is more common than WEE and is found widely in several regions of the United States, especially in areas with high mosquito populations.

Merck Animal Health Solutions

PRESTIGE® 5

PRESTIGE® 3 + WNV

PRESTIGE® 3

PRESTIGE® 4

PRESTIGE® 5 + WNV

Transmission Parasite Life Cycle

EEE and WEE are transmitted only by the bite of infected mosquitoes; direct transmission between horses and people does not occur.

Clinical Signs

Infection affects the central nervous system.

Moderate to high fever (>101.5)
Severe depression
Lack of appetite
Behavior changes
Impaired vision
Circling or head pressing
Muscle twitches
Inability to swallow
Weakness, incoordination
Paralysis of one or more limbs
Inability to stand
Convulsions, death

Risk Factors

High mosquito population
Standing water
Vaccination is recommended as a core protection strategy

References

“Eastern & Western Equine Encephalomyelitis,” American Association of Equine Practitioners, copyright 2020,
aaep.org/guidelines/vaccination-guidelines/core-vaccination-guidelines/easternwestern-equine-encephalomyelitis.

“Equine Encephalitis (EEE/WEE/VEE),” USDA Animal and Plant Health Inspection Service, Dec. 29, 2020,
www.aphis.usda.gov/aphis/ourfocus/animalhealth/animal-disease-information/equine/eee-wee-vee/equine-encephalitis.

“Eastern Equine Encephalitis (EEE),” Equine Disease Communication Center: Disease Fact Sheet, EDCC and AAEP, 2017, aaep.org/sites/default/files/Documents/Outside%20Linked%20Documents/DiseaseFactsheet_EEE%20Cobranded.pdf.

“Western Equine Encephalitis (WEE),” Equine Disease Communication Center: Disease Fact Sheet, EDCC and AAEP, 2017, https://aaep.org/sites/default/files/Documents/Outside%20Linked%20Documents/DiseaseFactsheet_WEE_FINAL%20Cobranded.pdf