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Animal and Plant Health Inspection Service
U.S. Department of Agriculture

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Equine Encephalitis (EEE/WEE/VEE)

Eastern equine encephalitis (EEE), western equine encephalitis (WEE) and Venezuelan equine encephalitis (VEE) are caused by Alphaviruses.  Birds and rodents are the primary reservoirs, but unvaccinated horses are particularly susceptible and often serve as sentinels.  These diseases are zoonotic, infecting humans, and are a public health concern.  Eastern equine encephalitis is the most common of the three and is found widely in several regions of the United States (especially in areas of high mosquito populations). Western equine encephalitis occurs infrequently, but circulates in wildlife. Venezuelan equine encephalitis is a Foreign Animal Disease and therefore reportable at both the Federal and State level.  It occurs in cycles in Central and South America; and there have been incursions into the United States decades ago. 


Infection causes non-specific clinical signs and often affects the central nervous system.

  • Fever
  • Severe depression “sleeping sickness”
  • Behavior changes
  • Impaired vision
  • Circling or head pressing
  • Muscle twitches
  • Inability to swallow
  • Paralysis
  • Convulsions, Death
  1. Contact your veterinarian immediately.
  2. Monitor other horses on the property for similar symptoms.

EEE/WEE/VEE are transmitted only by the bite of infected mosquitoes; direct transmission between horses and people does not occur.  However, should an incursion of VEE occur, equine infections do present some risk to people.

Treatment consists of supportive care.  Survival rates for horses infected with EEE or VEE is low; however, WEE survival can be as high as 70-80%.

EEE/WEE/VEE vaccination is very effective at preventing clinical disease.  Vaccination needs to be repeated at minimum on an annual basis.  Consult with your veterinarian regarding boosters if you live or are travelling to an area with year round mosquito populations or an area that has previously reported cases of EEE/WEE. As VEE has not occurred in the U.S. for over 40 years vaccination is not recommended unless the animal will be travelling to endemic areas.

Reduce your horse’s exposure to mosquitoes:  eliminate any standing water (mosquito habitat) and place fans inside where the horses rest, limit outdoor activities at dawn and dusk, and use equine approved mosquito repellent.

Annual Summary Reports 2006-2019.
Number of confirmed eastern equine encephalitis cases by State and County

Surveillance Information

Reports of equine cases of arboviral (i.e., arthropod-borne virus) diseases, including eastern and western equine encephalitis, are reported to ArboNet, an electronic-based surveillance and reporting system used to track and report arboviral activity. ArboNet captures laboratory-confirmed positive cases in humans, horses, other mammals, birds and mosquitoes across the United States. Equine case-finding varies by State, but primarily relies on passive reporting from private practitioners and diagnostic submissions. In some States, reporting is mandatory.

2019 Eastern Equine Enchephalitis Cases
Total Cases  184


2018 Eastern Equine Encephalitis cases
Total cases - 107

 


2017 Eastern Equine Encephalitis cases
Total cases - 86



2016 Eastern Equine Encephalitis cases
Total cases - 118    

   


2015 Eastern Equine Encephalitis cases
Total cases - 70


2014 Eastern Equine Encephalitis cases
Total cases - 136


2013 Eastern Equine Encephalitis cases
Total cases - 192


2012 Eastern Equine Encephalitis cases
Total cases - 209

2012 equine cases of eastern equine encephalitis


2011 Eastern Equine Encephalitis cases      
Total cases - 60

US map showing the number of Eastern Equine Encephalitis cases in 2011 in each State


2010 Eastern Equine Encephalitis cases      
Total cases - 247

Equine cases of Eastern Equine Encephalitis for 2010 - preliminary data


2009 Eastern Equine Encephalitis cases      
Total cases - 301

map - equine cases of eastern equine encephalitis in the US


2008 Eastern Equine Encephalitis cases      
Total cases - 185

Map of U.S.


2007 Eastern Equine Encephalitis cases       
Total cases - 206

2007 eastern equine encephalitis cases map


2006 Eastern Equine Encephalitis cases 
Total cases - 111


2005 Eastern Equine Encephalitis cases
Total cases - 330
(as reported to CDC's ArboNET reporting system)

2005 Eastern equine encephalitis cases


2004 Eastern Equine Encephalitis cases      
Total cases - 133 (as reported to CDC's ArboNET reporting system)

2004 Eastern equine encephalitis cases


2003 Eastern Equine Encephalitis cases      
Total cases - 712 (as reported to CDC's ArboNET reporting system)

2003 Eastern equine encephalitis cases

 

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