First EEE death in NY since 2015: What to know about the virus

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NEW YORK - The first person to contract eastern equine encephalitis—also known as triple E or EEE—since 2015 in New York, has died, according to New York Governor Kathy Hochul.

The extremely rare yet potentially fatal infection is caused by the bite of an infected mosquito and causes inflammation of the brain.

In response, the state has issued a declaration of an Imminent Threat to Public Health for EEE. This will essentially unlock resources to help with the prevention response.

"Following the first confirmed human case of EEE, my administration took statewide action to help protect communities," Hochul said.

The State Parks and DEC are providing mosquito repellent at park facilities, posting signs to raise awareness about EEE, and consulting with local health departments about limiting park hours during peak mosquito activity.

They are also alerting visitors about prevention measures, while launching a social media campaign to promote mosquito bite prevention, including using repellent and avoiding outdoor activity at dawn and dusk.

Here's what to know about the mosquito-borne disease.

What is eastern equine encephalitis, or triple E?

Eastern equine encephalitis is a virus that is primarily transmitted by certain mosquitoes. It was first identified in horses that died of encephalitis along the mid-Atlantic coast in 1933. EEE was recognized to cause human disease during an outbreak involving horses and humans in southeastern Massachusetts in 1938.

Since then, sporadic human and horse cases have been reported nearly every year in the Atlantic, Great Lakes and Gulf Coast regions of the U.S., with larger outbreaks occurring several years apart in these areas. The last significant outbreak of human EEE disease was in 2019 when over three dozen cases were reported, largely from Massachusetts and Michigan.

How is it transmitted?

EEE virus exists in a natural cycle between Culiseta melanura – the black-legged or black-tailed mosquito – living in eastern freshwater hardwood swamps and certain birds that reside in such swamps.

Culiseta melanura mosquitoes feed almost exclusively on birds and usually do not bite humans or horses. However, more common mosquitoes such as Aedes, Coquillettidia and Culex can sometimes bite infected birds, become infected themselves and then transmit EEE virus to nearby humans or horses. These are called "bridging" mosquitoes.

Rarely, EEE virus has also been transmitted through organ donation. Theoretically, it also may be transmitted by blood transfusion.

Why is EEE surfacing now?

Typically, there are about 10 human cases reported annually in the Atlantic, Great Lakes and Gulf Coast regions of the U.S., though there are likely many more mild cases that go unreported. Most human cases occur from July through October in endemic areas.

Every few years, there are much larger outbreaks of EEE disease in certain areas. For instance, in 2019, over three dozen cases were reported, primarily from Massachusetts and Michigan. These cyclic outbreaks are likely due to a complex interaction between temperature, rainfall, mosquito populations, bird immunity and bird migration patterns.

What are EEE’s main symptoms and how severe can an infection be?

Researchers do not have great estimates on how often people become sick after being infected with the virus. Our best estimate is that about 95% of infected people have either no or relatively mild symptoms. Some may develop fever or a flu-like illness after an incubation period of four to 10 days.

About 5% of people infected with EEE virus can go on to develop a brain swelling called encephalitis.

This brain swelling can be particularly severe and may require intensive care. Among those who develop encephalitis, approximately one-third die. The other two-thirds may have permanent neurologic deficits including cognitive problems, weakness or movement disorders.

People younger than 15 and older than 50, as well as those who are immunocompromised, are at higher risk of progressing to encephalitis.

Are there any treatments or vaccines for EEE?

There are no proven effective treatments for EEE at this time. Some clinicians have tried steroids to reduce swelling or antibodies to improve immune response, with variable success. But no treatments have been proven in large clinical trials.

Brain swelling may need to be managed in the intensive care unit, and seizures may need to be treated with anti-seizure medications. Almost all patients who develop encephalitis and survive will need prolonged rehabilitation.

There are currently no commercially available human vaccines for EEE, but there are vaccines for horses in endemic areas.