Mosquito-borne virus keeps people indoors at night

Residents of 10 Massachusetts communities have been warned to stay indoors from dusk to dawn. Some local parks are being closed at night. A person has died in Recent Hampshire. Pesticides are being sprayed from trucks and airplanes.

What’s causing all the alarm? A mosquito-borne virus called eastern encephalomyelitis, which is so occasional that most infectious disease experts have never seen a case. At least four states have reported human EEE infections this year.

Here’s what you need to know.

Is this a particularly bad year for EEE?

The virus is endemic to North America, meaning it is constantly present on the continent. The United States sees a handful of infections each year, mostly along the East Coast and around the Great Lakes. In 2019, there were save 38 casesthe largest epidemic in recent US history.

As of Tuesday, the Centers for Disease Control and Prevention four human cases have been reportedin Wisconsin, Recent Jersey, Massachusetts and Vermont. In addition, officials in Recent Hampshire one death was reported.

But experts say it’s too early to tell whether this year will be particularly bad. Mosquito-borne diseases typically spread widely by October, or until it gets icy enough that water freezes, said Dr. Jonathan Abraham, an infectious disease specialist at Harvard Medical School.

Until then, health services in affected areas are appealing to residents to take precautions.

Who should worry?

The main risk factor for contracting the virus is exposure to mosquitoes, said Dr. Cameron Wolfe, professor of infectious diseases at Duke University School of Medicine.

People who spend extended periods of time outdoors — including those who work outdoors, are homeless, or enjoy hiking or cycling — are at greater risk of contracting the virus, simply because they are more likely to be bitten by mosquitoes.

They should consider taking extra precautions, such as wearing long pants and shirts and using bug spray. It’s worth noting that not all outdoor areas are equally risky.

Dr. Wolfe says walking through downtown Manhattan is probably much less risky than spending time in the swamps and lowlands of South Carolina — an environment that mosquitoes love.

Where is the virus circulating?

In the EEE virus life cycle, humans are something of an accessory. In wetland ecosystems, mosquitoes feed on infected birds and then transmit the virus to well birds.

Some mosquito species feed on both birds and larger animals. It is these biting insects that infect humans. Humans cannot transmit the virus to other humans, and mosquitoes do not usually become infected by biting humans because humans do not have high concentrations of the virus in their blood. Humans are therefore considered “dead-end hosts.”

Similarly, other animals that can get the infection include ostriches, llamas, and, as the name suggests, horses. The EEE virus was first identified in the 1930s using cultures of infected horse brains.

What does this disease look like?

Most people infected with the EEE virus have no symptoms or flu-like symptoms that go away within a few weeks, According to the CDC But if the virus reaches the brain — which happens in less than 5 percent of cases — the prognosis becomes disastrous.

Once in the brain, the virus attaches to proteins on the surface of neurons and kills them, often causing eternal neurological damage. The body’s immune response, which leads to swelling and inflammation, can also damage the brain, said Dr. Kevin Gobeske, a neurologist in the critical care unit at Yale School of Medicine.

About 30 percent of patients who develop neurological symptoms die, according to the CDC. Survivors can suffer sedate and long-term health conditions, including paralysis, mental retardation and personality disorders.

Is there a treatment?

There is no specific treatment for the EEE virus, so doctors focus on treating symptoms with painkillers or, in severe cases, using steroids to control swelling. “We don’t have many good options,, Dr. Gobeske said.

It’s unclear why some people recover fully while others are hospitalized with EEE infections. There’s not enough evidence to say whether specific groups are more likely to develop severe disease, Dr. Abraham said.

Although there are vaccines for horses, none have been approved for humans. The disease is occasional and complicated enough that there has been no push to develop a vaccine for humans, Dr. Gobeske said.

The best preventative strategy is to limit exposure to mosquitoes by pouring out standing water, repairing damage to doors or windows, and in some high-risk areas, avoiding going outside after obscure.

Even if there have been no reported cases of EEE in your state, Dr. Wolfe recommends taking the following precautions to lend a hand avoid any mosquito-borne diseases, such as West Nile virus, which peak at this time of year.

“I don’t know of any good, well reason to be joyful about getting bitten by a mosquito,” he said. “It doesn’t matter whether it’s malaria, dengue fever or Eastern horse fever – there’s no particularly good outcome.”