Warm weather has finally returned to northern New England, but that means so have the mosquitos. More than 200 types of mosquitoes live in the United States and U.S. territories, and of those 200, 12 types can carry mosquito-borne illnesses, according to the Centers for Disease Control (CDC). We asked Elizabeth A. Talbot, MD, Infectious Disease and International Health, what we need to know about mosquito-borne illnesses and how to protect yourself and your family.
What is a mosquito-borne illness?
Mosquito-borne illnesses are diseases humans can get from the bite of an infected mosquito. A lot of these diseases are tropical, like Yellow Fever, West Nile Virus, Dengue, Zika, or malaria, which is the third leading cause of death from an infectious disease in the world (before COVID-19 pushed it to fourth).
New Hampshire numbers*
- Since 2003, there have been 7 cases of West Nile Virus identified in humans, most recently in 2017.
- Since 2004 there have been 15 cases of Eastern Equine Encephalitis identified in humans in NH, most recently in 2014.
- Since 2013, when it was first identified in New Hampshire, 14 cases of the Jamestown Canyon virus have been identified, most recently in 2021. Jamestown Canyon virus has become the primary cause of mosquito-borne illness in New Hampshire in the last 8 years.
*According to New Hampshire Department of Health and Human Services
Vermont numbers**
- There have been no documented cases of Jamestown Canyon virus in Vermont.
- Since 2002, West Nile virus has been detect 1 human case of West Nile virus was reported in 2021, however, Currently, the risk for West Nile virus is considered widespread in Vermont.
- No human cases of Eastern Equine Encephalitis were reported in 2021. The most recent Eastern Equine Encephalitis Virus was detected in mosquitos in 2015. The most recent human cases in Vermont were reported in 2012.
**According to Vermont Department of Health
Are there mosquito-borne illnesses in our area?
Unfortunately, yes. Mosquito-borne diseases transmitted in New Hampshire and Vermont include West Nile virus, Eastern Equine Encephalitis virus and, the most recent arrival, Jamestown Canyon virus. All three of these mosquito-borne illnesses are relatively rare (see sidebar) in both New Hampshire and Vermont, but that doesn’t mean we shouldn’t be cautious.
The occurrence of these infections is highly regional, with difference even between New Hampshire and Vermont, including whether or not the disease has been found in humans, or detected in tested mosquitos. Surveillance for these diseases in animals and mosquitos is not conducted systematically in all settings, so even if not identified in your neighborhood, you may still be at risk.
What are the symptoms?
A person with any of these three diseases can experience a range of symptoms—from no symptoms (asymptomatic) to having fever, chills, headache, fatigue and muscle aches to even having a severe neurological (nervous system) disease.
An estimated 80% of human West Nile virus infections don’t require medical care. Symptoms of more severe illness from West Nile virus could include high fever, headache, neck stiffness and disorientation, with a small percentage—maybe 1%—of those infected developing a severe neurological infection like meningitis—an inflammation of the fluid and membranes surrounding your brain and spinal cord, encephalitis—inflammation of the brain, or acute flaccid paralysis, an uncommon, but serious condition that causes muscle paralysis.
Eastern Equine Encephalitis tends to cause more severe disease. Approximately one-third of individuals who develop illness may develop severe encephalitis. Symptoms from this virus may include vomiting, diarrhea, seizures, behavioral changes or coma.
Although it may be that asymptomatic or mild cases do not come to medical attention, early estimates are that about half of known Jamestown Canyon virus patients end up in the hospital. Serious symptoms of this virus include stiff neck, confusion, loss of coordination, difficulty speaking or seizures.
Seek medical attention it you notice any of the above severe symptoms.
How can I protect myself and my family?
The greatest risk for mosquito-borne infection due to West Nile virus and Eastern Equine Encephalitis is between July and October, while the risk for Jamestown Canyon virus can be present as soon as the snow melts. Risk for these diseases decreases in the fall, after the daylight hours shorten and the first hard frosts kill active mosquitoes.
Here’s how you protect yourself and enjoy the outdoors:
- Adults should wear an Environmental Protection Agency (EPA)-registered insect repellent containing at least 30% DEET. Picaridin and oil of lemon eucalyptus are also effective. The CDC website lists others. Follow manufacturer instructions for applying insect repellent on children. Make sure to not use insect repellent on babies younger than 2 months old, or products containing oil of lemon eucalyptus or para-menthane-diol on children younger than 3 years old.
- Wear long-sleeved shirts and long pants. There is even clothing treated with permethrin, an insecticide that repels mosquitos and other biting insects.
- Since mosquitos are active during the day and night, you need to protect yourself whenever you are outside.
- Use screens on windows and doors.
- Keep mosquitos from laying eggs in or near standing water. Empty any standing water, such as dog bowls or small pools once a week.
If you are travelling
Every region of the U.S. and throughout the world has its own group of mosquito-borne diseases. If you are traveling to warm or topical areas, talk to your healthcare provider or check the CDC website for travel alerts or the government health agency for the area you are visiting.
For more information on mosquito-borne illnesses, you can check out these resources:
- A CDC map showing the current and past cases of mosquito-borne illness across the United States
- CDC’s mosquito resources webpage
- Vermont Department of Health
- New Hampshire Department of Health and Human Services