Mosquito-Borne Illnesses

Both Eastern Equine (horse) Encephalitis (EEE) and West Nile Virus (WNV) are spread to humans by the bite of a mosquito with the disease.

Eastern Equine Encephalitis (EEE) is a rare but serious virus spread by the bite of a mosquito with the disease, and has more severe symptoms than West Nile Virus (WNV). EEE is an arbovirus (short for arthropod-borne, meaning spread by insects). Birds are the source of infection for mosquitoes, which can sometimes spread the infection to horses, other animals, and, in rare cases, people.

West Nile Virus (WNV) was first seen in the US in 1999, in the New York City area of Queens. WNV can live in a number of types of birds and is passed bird to bird by certain types of mosquitoes. Occasionally, a mosquito with the disease will pass the virus to humans or other animals. Most healthy people do not get sick from the virus, but sometimes it may cause symptoms. When a human gets ill from WNV, they may have symptoms including encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord).

NOTE: Encephalitis and meningitis can also be caused by head injury, bacterial infections or, more commonly, other viral infections.

New Hampshire Arboviral Illness Surveillance, Prevention and Response Plan

DHHS Press Releases:

DHHS Identifies Jamestown Canyon Virus in Mosquito Batches in Atkinson and Hampstead (08/22/2022, press)

NH DHHS Identifies Season’s First Positive Test for West Nile Virus in Mosquito Batch in Manchester (07/28/2022)

The Spread Of EEE and WNV

EEE and WNV are spread to humans by the bite of a mosquito with the disease.

When a mosquito bites a bird with the disease, it then gets the disease.

The mosquito with the disease could then bite a human and spread the infection. Mosquitoes with the disease are the main known source for WNV and EEE being spread to humans. These viruses are not spread by person-to-person contact such as touching, kissing, or caring for someone who has the disease. No known spread from birds to people has happened; however, since dead birds may have the virus, one should not handle birds or any dead animals with their bare hands.

EEE and WNV Information for Providers

This section of the West Nile virus (WNV) and Eastern Equine Encephalitis (EEE) information area is specifically for healthcare providers, in order to provide them current information on human surveillance for cases of WNV and EEE.

Information may include, but will not be limited to:

  • Case definition,
  • Procedures for case reporting,
  • Health alerts,
  • Technical articles, and
  • Forms.

Please check back for updates and additions.

Prevention Guidelines

1. Eliminate standing water and other mosquito breeding locations.

In warm weather, mosquitoes can breed in any puddle that lasts more than 4 days!

  • Remove old tires from your property.
  • Dispose of tin cans, plastic containers, ceramic pots, or other containers. Don't overlook containers that have become overgrown by aquatic vegetation.
  • Drill holes in the bottom of recycling containers that are left outside.
  • Make sure roof gutters are clean and draining properly.
  • Clean and chlorinate swimming pools and hot tubs. If not in use, keep empty and covered and keep covers free of standing water.
  • Aerate garden ponds or stock them with fish.
  • Turn over wheelbarrows and change water in birdbaths at least twice weekly.
  • Turn over plastic wading pools when not in use.
  • Remind or help neighbors to eliminate breeding sites on their properties.

2. Be aware of where mosquitoes live and breed, and keep them from entering your home.

  • Mosquitoes lay their eggs in standing water. Weeds, tall grass, and bushes provide an outdoor home for the adult Culex pipiens mosquito (the common northern house mosquito), which is most commonly associated with the West Nile Virus.
  • Mosquitoes can enter homes through windows or doors with broken or no screens. Make sure doors and windows have tight-fitting screens. Repair or replace all screens in your home with tears or holes.
  • Resting mosquitoes can often be flushed from indoor resting sites by using sweeping motions under beds, behind bedside tables etc. and once in flight, killed prior to sleeping at night.

3. Protect yourself from mosquito bites.

  • If outside during evening, nighttime, and dawn hours, when mosquitoes are most active and likely to bite, children and adults should wear protective clothing such as long pants, long-sleeved shirts, and socks.
  • Consider the use of an effective insect repellent, such as one containing DEET.
    • Repellent containing 30% or less DEET (N,N-diethyl-methyl-meta-toluamide) are advised for use by children and adults.
    • Use DEET according to the manufacturer's directions.
    • Children should not apply DEET to themselves.
    • Repellents that contain Picaridin or oil of lemon eucalyptus have also been determined to be useful.
  • Vitamin B, ultrasonic devices, incense, and bug zappers have not been shown to be useful in preventing mosquito bites.


NH Arbovirus Testing Results




Arboviral Surveillance

Arboviral Surveillance Summary 2021

Arboviral Surveillance Summary 2020

Arboviral Surveillance Summary 2019

Arboviral Surveillance Summary 2018

Arboviral Surveillance Summary 2017

Arboviral Surveillance Summary 2016

Arboviral Surveillance Summary 2015

Arboviral Surveillance Summary 2014

Arboviral Surveillance Summary 2013

Arboviral Surveillance Summary 2012

Arboviral Surveillance Summary, 2011

Arboviral Surveillance Summary, 2010

Arboviral Risk Map

Arboviral Risk Map 2022

Arboviral Risk Map 2021

Arboviral Risk Map 2020

Arboviral Risk Map 2019

Arboviral Risk Map 2018

Arboviral Risk Map 2017

Arboviral Risk Map 2016

Arboviral Risk Map 2015

Arboviral Risk Map 2014

Arboviral Risk Map 2013

Arboviral Risk Map 2012

Arboviral Risk Map 2011

Arboviral Risk Map 2010

Protect yourself from mosquito and tick bites by using an EPA-registered insect repellent whenever you go outside.

Protect yourself from mosquito and tick bites by using an EPA-registered insect repellent whenever you go outside.