What You Need to Know About Triple E — Eastern Equine Encephalitis (EEE)

Medical | Heather Marshall, PhD| October 02, 2019

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If you live in New England or Michigan, chances are you’re hearing a lot about Eastern Equine Encephalitis (EEE). Here’s what physicians need to know.

Eastern Equine Encephalitis (EEE, colloquially known as “Triple E”) is a viral infection transmitted by mosquitoes. Triple E is a severe and potentially fatal disease; in cases where EEE doesn’t kill, survivors often have disabling neurologic problems. Typically, there are only a handful of cases of EEE each year, primarily restricted to the Atlantic and Gulf Coast states and Great Lakes region of the United States but cases have been reported elsewhere.

Triple E starts as a flu-like illness about a week after the infecting mosquito bite. Early symptoms are general and include fever, chills, malaise, and myalgia. Abrupt encephalitis with severe headache and disorientation can follow, and seizures and coma are possible thereafter. There is no treatment, and infection is fatal in about one-third of patients.

Preliminary diagnosis is often established in patients with a combination of clinical features, findings on brain imaging, areas of residence or travel, and local epidemiology. While laboratory diagnosis can be confirmed by detection of EEE virus-specific antibodies in cerebrospinal fluid, some patients test negative, so it’s not a useful test to rule out EEE. In fatal cases, nucleic acid amplification, histopathology, and/or virus culture of autopsy tissue can establish diagnosis post-mortem.

Preventing mosquito bites is the most effective way to reduce the chance of EEE infection.

People who reside in or travel to areas where EEE is present — particularly those who engage in outdoor work or recreational activities — are at risk of infection in summer and early fall. Currently, a total of 29 cases have been reported in Massachusetts (twelve), Michigan (nine), Rhode Island (three), New Jersey (three), and Connecticut (two), and eight patients have died.

Tracking EEE also includes testing mosquitoes and animals. Like humans, horses and occasionally other animals can become infected. Mosquito sampling allows public health officials to appropriately warn their communities and initiate mosquito control efforts such as targeted insecticide ground spraying and over-night aerial spraying. 

Interestingly, a vaccine has been developed, but it is poorly immunogenic and is only used for at-risk laboratory personnel. Preventing mosquito bites is the most effective way to reduce the chance of EEE infection. Recommendations from the CDC include:

  • Using Environmental Protection Agency (EPA)-approved insect repellents on skin and clothing
  • Wearing long-sleeved shirts and long pants while outdoors
  • Limiting time outdoors at dawn, dusk, and early evening
  • Taking steps to control mosquitos at home by
    • Using intact screens on windows and doors
    • Eliminating mosquito breeding sites (standing water)

While Triple E is all over the news in our area (EBSCO is located along the picturesque Ipswich River in Ipswich, Massachusetts), it’s important to remember that it is a rare disease. Mosquito avoidance is the best defense, and as the weather cools and the leaves start changing color, we are reminded that the first frost — that is, the end of the mosquito season — is on its way.

Eastern Equine Encephalitis topic in DynaMed

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Heather Marshall, PhD
Senior Medical Writer and Digital Media Specialist, DynaMed

Written by Heather D. Marshall, PhD, Senior Medical Writer and Digital Media Specialist at DynaMed. Edited by Vito Iacoviello, MD, Deputy Editor for Infectious Disease, Rheumatology, and Immunology at DynaMed. 

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