New Hampshire resident dies after testing positive for mosquito-borne encephalitis virus

A New Hampshire resident infected with the mosquito-borne eastern equine encephalitis virus has died, state health authorities said.

The Hampstead resident’s infection was the first in the state in a decade, the New Hampshire Department of Health and Human Services said Tuesday. The resident, whom the department only identified as an adult, had been hospitalized due to severe central nervous system symptoms, the department said.

About a third of people who develop encephalitis from the virus die from the infection, and survivors can suffer lifelong mental and physical disabilities. There is no vaccine or antiviral treatment available for infections, which can cause flu-like symptoms and lead to severe neurological disease along with inflammation of the brain and membranes around the spinal cord.

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

Nationally, the burden of eastern equine encephalitis can vary from year to year. There are typically about 11 human cases in the U.S. per year, according to the U.S. Centers for Disease Control and Prevention. There were seven cases nationally last year, but more than 30 in 2019, which was a historically bad year in which at least a dozen patients died, according to federal data.

The 2019 outbreak included six deaths among 12 confirmed cases in Massachusetts, and the outbreak continued the following year with five more cases and another death. Two of the three people infected in New Hampshire in 2014 died.

This year, human infections have been confirmed in New Jersey, Wisconsin, Massachusetts and Vermont as well as New Hampshire, according to the CDC.

The New Hampshire health department said the virus has also been detected in one horse and several mosquito batches in New Hampshire this summer. Mosquitoes that carry the virus can sometimes be found in developed areas that used to be swamp land where they can still find habitat, Ellison said.

Public health authorities in states where mosquito-borne infections happen encourage people to take precautions, preventing mosquito bites by using repellent, wearing long sleeves and pants and avoiding outdoor activity in the early morning and evening when mosquitoes are most active. Removing any standing water where mosquitoes breed also is important.

“We believe there is an elevated risk for EEEV infections this year in New England given the positive mosquito samples identified. 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,” said New Hampshire epidemiologist Dr. Benjamin Chan.

In Massachusetts, several towns have urged people to avoid going outdoors at night this summer because of concerns over this virus, one of several diseases mosquitoes can spread to humans. Massachusetts authorities planned to begin spraying Tuesday in some communities to prevent the spread.