Are Mosquitoes Bad in New Hampshire?

The three tracked arboviruses: Eastern Equine Encephalitis (first NH human case 2004, ~30% fatality), West Nile Virus (first NH human case 2003), and Jamestown Canyon Virus (19 locally acquired cases since 2013). The structural problem: NH has no statewide mosquito control board, no regional districts, and no aerial spraying program. Towns hire private contractors individually. Massachusetts, by contrast, operates 11 mosquito-control districts with aerial capability.

The acidic hardwood swamps of the Kingston-Brentwood-Danville-Hampstead corridor are the premier Culiseta melanura habitat. Both human EEE cases in 2024 fell in southeastern towns (Hampstead and Kensington). Merrimack Valley (Manchester/Nashua/Concord): NH's West Nile hotspot. Urban catch basins are Culex pipiens breeding grounds; Manchester has run its own arbovirus program since 2000. Seacoast/Great Bay: Enormous Ochlerotatus cantator biting pressure from salt marshes — high nuisance, historically less disease. Strafford and eastern Hillsborough counties: Elevated EEE risk. Lakes Region and North Country: Heavy nuisance populations from shoreline wetlands but labeled 'Baseline/No Data' by DHHS because trapping is limited to the southeast.

The second case, an adult from Kensington, was hospitalized but survived. Both human cases were in southeastern towns, with symptom onset in August; positive mosquito batches were detected across the Rockingham County corridor (Danville, Kingston, Newton, Fremont, Hampstead, Kensington). NH DHHS also confirmed 1 infected horse and 7 EEE-positive mosquito batches that season. This wasn't a one-off: NH led the nation in 2005 (7 cases, 2 deaths) and had 3 cases / 2 deaths in 2014. EEE cycles on a roughly 5–10 year regional periodicity.

Vermont had 2 human EEE cases (first since 2012) with 86 positive mosquito batches across 16 towns. Massachusetts had 5 EEE and 7 WNV human cases with 11 mosquito control districts providing aerial response. Rhode Island had 1 EEE and 6 WNV cases. Maine had 1 EEE and 2 WNV cases. Connecticut had 0 EEE but 9 WNV cases. Several New England states saw EEE re-emerge in 2024, and Massachusetts — with the most human cases — has vastly superior control infrastructure than NH.

Paradoxically, drought increases WNV risk because Culex and birds concentrate at shrinking water sources (Cape Cod Mosquito Control 2025). Mild winters improve Culex diapause survival. And the climate angle: NH winters have warmed faster than first-frost dates, meaning overwintering Culex survive better. Aedes albopictus — a daytime biter already established in Vermont since 2019 — is expected to push into NH as winters warm.