New Hampshire Reports First Mosquito-Borne Encephalitis Death in a Decade

The New Hampshire State House, the state Capitol building of New Hampshire, in Concord, N.H., on Feb. 16, 2023. Michael M. Santiago/Getty Images

A New Hampshire resident who was infected by the mosquito-borne Eastern Equine Encephalitis (EEE) virus has died, state health officials said.

On Aug. 27, the New Hampshire Department of Health and Human Services reported the death of the infected individual, identified only as an adult from Hampstead, a town in the southeastern part of the state near the Massachusetts border. The patient died after being hospitalized with “severe central nervous system symptoms,” the department said.

The last reported human infection with the EEE virus in New Hampshire occurred in 2014, when health officials identified three cases, two of which resulted in death. Described as “rare but serious,” the virus has also been detected in one horse and several mosquito batches in the state so far this summer.

“In New Hampshire, mosquitos transmit infections including Eastern Equine Encephalitis Virus, West Nile Virus, and Jamestown Canyon Virus,” Dr. Benjamin Chan, the New Hampshire state epidemiologist, said in a statement announcing the latest fatality.

“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.”

In the past week, the EEE virus has been detected in neighboring states, with one human infection reported in Massachusetts and another in Vermont. Several towns in central Massachusetts have urged residents to stay indoors from dusk to dawn, when many mosquito species are most active.

In addition to avoiding outdoor activities in the peak mosquito hours, people living in high-risk areas are advised to use mosquito repellents, wear long sleeves and pants when outside, and make sure their homes’ doors and windows have tight-fitting screens without holes.

It’s also important for them to drain or discard items that collect standing water, such as buckets, tires, flowerpots, and birdbaths, to prevent mosquitoes from breeding.

There are no vaccines to prevent or medicines to treat EEE. The disease can cause flu-like symptoms such as fever, chills, muscle aches, and joint pain and can also lead to severe neurological disease, along with inflammation of the brain and membranes around the spinal cord.

Nationwide, an average of 11 cases of EEE virus infections are reported each year, mostly in Eastern or Gulf Coast states, according to the U.S. Centers for Disease Control and Prevention. Approximately one-third of people who develop encephalitis from the virus die.

“Persons over 50 years of age and under 15 years of age seem to be at greatest risk for developing severe disease when infected with EEE virus,” the agency stated on its website.

Humans and other animals that contract the virus are considered “dead-end hosts,” which means there is no subsequent human-to-human, animal-to-human, or human-to-animal transmission.

Many people who recover from EEE are left with long-term physical or mental problems, according to the CDC. These can range from mild to severe intellectual disability, personality disorders, seizures, paralysis, and cranial nerve dysfunction. Survivors with severe disease and ongoing disabilities often require long-term care and die within a few years.