EEE: A worried parent’s questions, answered

EEE guide: answers to all your questions

If you’ve been watching the news recently, you’re probably aware that there are currently seven confirmed human cases of Eastern equine encephalitis (EEE) in Massachusetts. This year ties with 2012 as the third largest outbreak of EEE within the state in its history.

School sports practices and outdoor evening events have been cancelled and parents are panicked. We sat down with Dr. Asim Ahmed from the Division of Infectious Disease at Boston Children’s Hospital, to answer all our questions about EEE.

What is Eastern equine encephalitis (EEE)?

EEE is a virus spread by the bite of infected mosquitoes. Inflammation of the brain, or encephalitis, is a frequent and life-threatening complication of EEE that may also lead to permanent neurological damage or coma.

This is one of the most dangerous viruses on the planet, and it’s right here in our own backyard.”

Dr. Asim Ahmed

“People often associate dangerous infectious diseases with exotic, faraway places but you don’t have to go to West Africa or the Congo to find a dangerous virus with a 50 percent mortality rate,” says Ahmed. “This is one of the most dangerous viruses on the planet, and it’s right here in our own backyard.”

Why are there so many cases of EEE this year?

Every summer, Massachusetts surveys the state for mosquitoes that carry the virus. Historically, the areas of peak activity are found in Southeastern Massachusetts between Bristol and Plymouth counties near an area called the Hockomock swamp, which is the traditional breeding ground of the mosquito that amplifies the virus in nature. But when the risk is very high, other non-traditional areas become higher risk areas, which is why we’re hearing about EEE in the middle of the state, the northeast corner and even Western Mass.

Families should remember that EEE is very rare, even during peak years.

Ahmed thinks that periodically there are introductions of novel strains of the virus in our local environment. In addition, “certain ecological conditions likely favor the abundance of the type of mosquito that spreads the virus in nature,” he says. “During those times, the virus can root in less traditional places and those become little factories for amplification of the virus.”

What are the signs and symptoms of EEE?

It’s important to distinguish between early warning signs that may begin 4 to 10 days after a mosquito bite, and the neurological symptoms specific to EEE — and understand how they relate to each other.

Early symptomsNeurological symptoms
General malaiseStiff neck
NauseaSensitivity to light
Altered or declining mental status

In a 2013 research paper published in Emerging Infectious Diseases, Ahmed and co-authors examined 15 cases of children treated for EEE at Boston Children’s between 1970 and 2010. They found that patients with a longer “prodrome” or period of early symptoms experienced a slower progression of neurologic symptoms, likely because their immune systems quickly triggered to fight and contain the infection. “But if the time between early symptoms and neurological symptoms was short, the prognosis was very, very poor,” says Ahmed.

How can I protect my family?

In a season like this where there are high levels of the virus in the environment, families should not panic, but be smart by taking protective measures. And remember that EEE is very rare. The four most important things you can do to protect yourself and your family:

  1. Use insect repellant
  2. Wear clothing that covers the arms and legs
  3. Avoid peak mosquito activity from dusk until dawn
  4. Drain any area around your house, however small, that collects water

When can I stop worrying about EEE?

Historically, the end of August through mid-September presents the highest risk. But that risk continues until the first frost, so it’s important to continue to use protective measures through October and into November. 

Ahmed says it’s always hard to predict future risk, but notes that EEE epidemics have tended to occur in two- to three-year clusters, and then wane for several years. 2012 was the last big year, with seven human cases. These patterns should be studied, he says. “When we’re in the middle of an epidemic, we’re thinking about how to best keep people safe, but there does need to be that pivot once we’ve handled the acute period.” He acknowledges that this kind of study would require a sizeable infrastructure and coordination across different states, industries, and disciplines.

“I hope this year of very high EEE activity inspires a national coordinated effort among physicians, scientists, and public health officials at the CDC, NIH, and state health departments to investigate the factors that lead to these periodic EEE epidemics. They have the infrastructure and resources in place to step back and figure out what’s going on here,” says Ahmed.

Learn more about Eastern equine encephalitis (EEE).

About our expert: Dr. Asim A. Ahmed is a physician and researcher in the Division of Infectious Disease at Boston Children’s Hospital. He has a long-standing clinical and scientific expertise in EEE and other arboviruses. His most recent research efforts are focused on the use of next-generation sequencing (or “deep-sequencing”) for pathogen detection to assist in the diagnosis of infectious diseases.

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