A New Hampshire resident has died from Eastern equine encephalitis (EEEV), a rare mosquito-borne brain infection, marking the first U.S. human fatality from the virus this year, health officials confirmed on Tuesday. This case represents New Hampshire’s first human EEEV infection in a decade and is the fifth reported in the U.S. this summer.
The victim, an adult from Hampstead in southeastern New Hampshire, tested positive for the virus and was hospitalized with severe central nervous system symptoms before succumbing to the illness, according to the state’s Department of Health and Human Services.
This year, four other nonfatal EEEV cases were reported to the Centers for Disease Control and Prevention (CDC) across the U.S.—one each in Massachusetts, Vermont, Wisconsin, and New Jersey. The last occurrence of a human EEEV case in New Hampshire was in 2014, with three documented infections, two of which were fatal.
Alongside the recent human case in New Hampshire, the virus has also been detected in a horse and seven mosquito samples within the state. Massachusetts reported its first human case since 2020 in an 80-year-old man from Worcester County, alongside findings of the virus in one horse and 60 mosquito samples. Vermont has reported 47 mosquito samples testing positive for the virus.
New Hampshire’s state epidemiologist, Dr. Benjamin Chan, noted the elevated risk of EEEV infections this year in New England, emphasizing that the threat will persist until a hard frost reduces the mosquito population. Residents are advised to minimize outdoor exposure, especially during peak mosquito activity.
Currently, Massachusetts health officials have designated at least 10 communities in Plymouth and Worcester counties near Boston as high or critical risk areas for EEEV.
Eastern equine encephalitis virus can cause severe flu-like symptoms, including fever, chills, muscle aches, and joint pain. In severe cases, it leads to neurological conditions such as encephalitis (brain inflammation) and meningitis (inflammation of tissues around the spinal cord). While only 4% to 5% of infected individuals develop encephalitis, the disease is fatal in approximately one-third of those cases, with many survivors facing lifelong disabilities. No vaccine or antiviral treatment is currently available.
On average, 11 human EEEV cases are reported annually in the United States. Since the CDC began tracking in 2003, the highest number of annual human cases was recorded in 2019, with 38 infections.
Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security, highlighted that the greatest risk of human EEEV infections is in New England and some Gulf Coast states, where mosquito and bird populations contribute to the virus’s cyclical presence. “While infections are rare, their high lethality demands significant public health attention,” Adalja stated.