New Hampshire Resident Dies From Rare but Serious Mosquito-Borne Illness

An adult in New Hampshire has died from an infection with Eastern equine encephalitis, a rare but serious disease caused by a virus spread by mosquitoes, according to a statement from the New Hampshire Department of Health and Human Services (DHHS).

Three other cases of the disease, which can cause inflammation of the brain in extreme situations, have been reported in the United States so far this year: one in Massachusetts, one in Vermont and one in Wisconsin, per the Centers for Disease Control and Prevention (CDC).

An average of 11 human cases of Eastern equine encephalitis are reported in the U.S. annually, according to the CDC. But the disease is often lethal—about 30 percent of people with Eastern equine encephalitis die, and many who survive continue to have neurologic problems. There are no vaccines or medications to treat the disease.

Two counties in Massachusetts began aerial and truck-based spraying of insecticides on Tuesday due to the risk for human disease. The town of Plymouth is now closing its public parks and fields from dusk to dawn due to the town’s high risk status, per the New York Times’ Amanda Holpuch.

Health officials recommend people take action to avoid infection, including using repellents and wearing clothing with high coverage when outdoors, as well as avoiding outdoor activity between dusk and dawn.

Most cases of Eastern equine encephalitis in the U.S. occur in eastern and Gulf Coast states. The virus circulates between mosquitoes and birds typically found in freshwater, hardwood swamps. Humans can get infected with the virus through a mosquito bite, but infected humans do not spread the virus to other people.

Most people infected with the virus don’t develop symptoms—only about 4 to 5 percent go on to develop Eastern equine encephalitis, per the CDC. People under 15 and over 50 have the greatest risk of developing severe disease. Since 2003, there have only been five years with more than ten cases reported in the country. The year with the most cases in that timespan was 2019, with 38 cases.

People who develop symptoms typically do so between four and ten days after a bite from an infected mosquito. Many infections will result in fever, chills, body aches and joint pain, though in rarer cases, infected people can develop neurologic disease, such as inflammation of the brain, known as encephalitis, or inflammation of the membranes around the brain and spinal cord, known as meningitis. Symptoms of the more severe condition can include fever, headache, vomiting, diarrhea, seizures, behavior changes, drowsiness and coma.

“Among the 4 to 5 percent that get infected and get the disease, only about a third of those people will get the most severe and awful version of the disease, which is the encephalitis,” Stephen Rich, a microbiologist at the University of Massachusetts Amherst, tells the New York Times.

“When it does cause an infection, it is very, very severe. Although it’s a very rare infection, we have no treatment for it,” Richard Ellison, an infectious disease specialist at University of Massachusetts Memorial Medical Center, tells Patrick Whittle of the Associated Press. “Once someone gets it, it’s just—all we can do is provide supportive care, and it can kill people.”

The person who died in New Hampshire was hospitalized due to severe central nervous system disease, per the DHHS statement. There hadn’t been an infection reported in the state since 2014, when there were three cases and two deaths. The case in Massachusetts is the state’s first since 2020, according to the Massachusetts Department of Public Health.

Eastern equine encephalitis virus (EEEV) has been detected this year in seven mosquito batches in New Hampshire, 69 mosquito samples in Massachusetts and 47 mosquito samples in Vermont, per the New Hampshire DHHS.

“We believe there is an elevated risk for EEEV infections this year in New England given the positive mosquito samples identified,” New Hampshire state epidemiologist Benjamin Chan says in the statement. “The risk will continue into the fall until there is a hard frost that kills the mosquitos. Everybody should take steps to prevent mosquito bites when they are outdoors.”

Will Sullivan | | READ MORE

Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.