Eastern Equine Encephalitis (EEE) in New Hampshire

The 2005 outbreak produced seven human cases and two deaths — at the time the most of any state that year — and represented the first laboratory-confirmed, locally acquired human EEE cases in NH in 41 years of national surveillance (CDC MMWR). Three human cases and two deaths followed in 2014. Then nothing for a decade. In 2024, the virus re-emerged sharply: five NH residents were confirmed infected with EEEV in August, with positive mosquito batches in Danville, Kingston, Newton, Fremont, Hampstead, and Kensington. The first case was a previously healthy 41-year-old Hampstead man, publicly identified as Steven Perry, who was hospitalized August 12 and died August 19, 2024 — the first U.S. EEE death of the year. A second NH fatality was reported in a Danville adult whose illness began in August. At least one infected horse was also identified in the cluster.

This mosquito breeds in cryptic pools beneath freshwater hardwood swamps, particularly red maple swamps and Atlantic white cedar swamps characteristic of southeastern NH. Critically, Culiseta melanura feeds almost exclusively on birds and rarely bites humans directly. Human transmission happens through 'bridge vectors' — mosquitoes that feed on both birds and mammals: Coquillettidia perturbans, Aedes canadensis, Aedes vexans, and Aedes sollicitans. Because these vectors breed in natural wetlands rather than backyard containers, EEE is far harder to control through residential source reduction than West Nile Virus. You cannot drain a red maple swamp.

Historically high-risk towns cluster in the southeastern ecological belt: Hampstead, Danville, Kingston, Newton, Sandown, Brentwood, Fremont, Epping, and Kensington — all places where Culiseta melanura swamp habitat and residential areas overlap. This ecological belt extends into Essex County, Massachusetts, and York County, Maine. Residents of these communities face meaningfully higher risk than NH residents overall, particularly from late July through September.

The case-fatality rate is approximately 30% for all cases and climbs to 64% in patients over 70 — roughly three times that of neuroinvasive West Nile Virus. There is no licensed human vaccine (a veterinary vaccine exists for horses and is widely used in southeastern NH). There is no specific antiviral treatment — ICU care, mechanical ventilation, and seizure management are the only interventions available. EEE progresses rapidly, with patients moving from vague flu-like symptoms to coma within days. And unlike WNV, which preferentially targets older adults, EEE severely affects children under 15 and adults over 50 alike — and as the 2024 Hampstead case demonstrated, it can also kill previously healthy middle-aged adults.

Seek emergency care immediately if, during July through October in southeastern NH, you develop sudden high fever combined with any of the following: severe headache, stiff neck, confusion or disorientation, seizures, muscle weakness, or loss of coordination. Do not wait to see if symptoms improve on their own. Tell the emergency department about recent mosquito exposure and your location. Early supportive ICU care can be life-saving even without antivirals. The NH DHHS Bureau of Infectious Disease Control ((603) 271-4496) coordinates arboviral testing for NH clinicians.