What is EEEV? Everything you need to know about mosquito-borne virus

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A New Hampshire man has become the first in the United States to die in 2024 from the eastern equine encephalitis virus (EEEV), a rare-but-dangerous mosquito-borne illness that has no cure or vaccine. Here’s everything you need to know about EEEV.

When was EEEV discovered?

Eastern equine encephalitis was first discovered in the brains of horses nearly two centuries ago, according to the Cleveland Clinic, an academic medical centre in Ohio. (Other sources say it was first discovered in the 1930s).

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How is EEEV spread?

The virus is spread between mosquitoes and infected birds, usually in hardwood swamps. The mosquitoes, which have become infected, can spread the virus to other animals, if they’re the sort of mosquitoes that feed on different species.

Horses and humans cannot spread the virus between one another or even back to mosquitoes.

However, there was one situation where a human organ donor gave organs to three other people, and the infection was passed along (although the U.S. Centers for Disease Control (CDC) does not say if all three organ recipients fell ill.)

It is just one of the many illnesses that can be spread by the mosquito — the deadliest animal on Earth.

Where is EEEV found?

In the U.S., the virus can be found in east coast states, the Gulf Coast and the Great Lakes region. There is a western equine encephalitis virus, but there have only been five cases in humans in the United States since 1987, and it’s considerably less dangerous than its eastern cousin.

There have been four other cases of EEEV so far this year, according to the CDC. The cases have occurred in humans in Vermont, Massachusetts, New Jersey and Wisconsin.

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Eastern equine encephalitis virus is found outside the United States too, including South and Central America, Europe and Asia.

Is EEEV found in Canada?

Yes. Migratory birds can bring the virus to Canada, and there are mosquito species within Canada that feed on birds and mammals.

The first case in Canada was reported in 2016. Ontario has, over the years, reported three human cases. If it’s found in horses, the illness must be reported to the Canadian Food Inspection Agency. As of mid-August, there were six cases in horses, all in Quebec and Ontario, CTV News reported.

Why is EEEV so dangerous?

There is no vaccine for humans for EEEV. There is, however, a vaccine for horses.

The majority of people who get the virus do not show symptoms. Others may develop what the CDC calls “febrile illness,” which includes fever, chills and aches and pains.

But the far riskier outcome is that there is neurological damage from an infection. This could include meningitis, which is when the membranes around the brain and spinal cord become inflamed, or encephalitis, which is inflammation of the brain.

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In fact, one-third of all humans infected with EEEV die. Even many of those who recover will be left with permanent mental or physical disabilities, including personality disorders, seizures and paralysis. They often require long-term care and, according to the CDC, “die within a few years.”

The virus is deadly enough that the U.S. studied it as a potential biological weapon, before it suspended its research program in 1969, according to the James Martin Center for Nonproliferation Studies.

What is the treatment?

There is no specific treatment. If a person goes into a coma, though, the usual hospital processes, such as intravenous fluids and ventilation, will be used to try and keep them alive. Medication that reduces fever and controls pain can also be used.

Do I need to worry?

Not really. The virus is incredibly rare. Less than 200 people have become infected since 2003 in the U.S. In 2019, there was a significant spike in the country, with 38 human cases. Researchers have attempted to sort out the factors that caused such a spike, but the results are unclear. One would suppose, for example, that more time spent outdoors versus indoors would have an impact on rates of infection, but a study found little changes in these habits between 2018 and 2019.

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“A large mosquito population, enabled by warm and wet conditions, is necessary, and an increase in years with warm and wet summers and mild winters may increase the frequency of outbreaks,” the study concluded.

That said, there are several ways for humans to protect themselves, including using insect spray with DEET, and wearing long-sleeved shirts and long pants while outdoors in areas where the virus can be prevalent.

Out of an abundance of caution, officials in Plymouth, Massachusetts, have closed parks from dusk until dawn, citing the high risk of EEEV in the area. The state is also spraying insecticide in order to kill mosquitoes that may be carrying the virus, and urging residents in parts of the state to stay indoors at night.

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