Mosquitoes and Health: How to Protect Your Family from the Pests

As the weather warms up, you'll see more mosquitoes. The tiny insects can be more than just an annoyance. While some mosquito bites will only itch, others can carry potentially dangerous illnesses, including easter equine encephalitis (EEE) and West Nile virus (WNV).

“It’s important to take steps to avoid mosquito bites,” said Dr. Joe Sills, chief of Emergency Medicine for Baystate Medical Center. “Some mosquitoes carry germs that can make people and some animals sick. In Massachusetts, the diseases linked to mosquitoes are West Nile virus (WNV) and eastern Equine Encephalitis (EEE) virus. Most people won't experience symptoms from either virus, but there are important differences to be aware of.”

Where Do Mosquitoes Live?

According to the Massachusetts Department of Public Health, there are over 3000 different kinds, also called species of mosquitoes identified worldwide, with more than 150 different kinds of mosquitoes found in North America. Fifty-one different kinds of mosquitoes have been found in Massachusetts.

Mosquitoes are attracted to carbon dioxide, a gas that humans and other animals breathe out and they can follow a stream of carbon dioxide from as far as 50 feet away.

Mosquitoes need stagnant water to lay their eggs. What most people don't realize is the surprising number of areas around their own house where mosquitoes can find the stagnant water they need. All a female adult mosquito needs is a bottle cap of water to lay 100 to 200 eggs. Once the eggs are laid, they hatch into larvae within 24 to 48 hours, so any temporary body of water that is present for more than a week can be a mosquito breeding habitat.

What is Eastern Equine Encephalitis?

Eastern equine encephalitis, also called EEE, is relatively rare in humans, although there are occasional outbreaks in certain regions of the country. Outbreaks of EEE usually occur in Massachusetts every 10 to 20 years. These outbreaks will typically last two to three years. The most recent outbreak of EEE in Massachusetts began in 2019 and included twelve cases with six fatalities. The outbreak continued in 2020 with five cases including one fatality. The risk of getting EEE is highest from late July through September when more mosquitoes are present and active.

“It is possible that some people who become infected with mosquito-borne viruses may not develop any symptoms or in some cases only flu-like symptoms,” said Dr. Sills. “The incubation period for the virus from the time of an infected mosquito bite to onset of illness ranges from four to ten days and the illness can last one to two weeks. There is no specific treatment for EEE. Antibiotics are not effective against viruses, and no effective anti-viral drugs have been discovered for the treatment of EEE,” said Dr. Sills. “Severe illnesses are treated by supportive therapy, which may include hospitalization, respiratory support, IV fluids and prevention of other infections.”

What is West Nile Virus?

West Nile virus (WNV) is a mosquito-carried virus most commonly spread to people through the bite of an infected mosquito. Because most people who are exposed to WNV have no symptoms, it is difficult to know exactly how many people have been infected. People who develop severe illness with WNV are most often reported. Between 2014 and 2023, 131 people were reported with WNV infection in Massachusetts. Eight of these people died. Cases have been identified from around the state.

“The majority of people who are infected with WNV (approximately 80%) will have no symptoms,” said Dr. Sills. “A smaller number of people who become infected, less than 20% will have symptoms such as fever, headache, body aches, nausea, vomiting, and sometimes swollen lymph glands. Less than 1% of people infected with WNV will develop severe illness, including encephalitis or meningitis. There is no specific treatment for WNV infections,” said Dr. Sills. “People with mild WNV infections usually recover on their own. People with severe WNV infections almost always require hospitalization.”

How to Protect Yourself and Your Family from Mosquito Bites

Dr. Sills encourages community members to follow the Department of Public Health tips that will help people protect themselves and their loved ones from illnesses caused by mosquitoes. Try these mosquito control tactics:

• Be aware of peak mosquito hours: The hours from dusk to dawn are peak biting times for many mosquitoes. Consider rescheduling outdoor activities that occur during the evening or early morning.
• Apply insect repellent when outdoors: Use a repellent with DEET (N, N-diethyl-m-toluamide), permethrin, picaridin (KBR 3023), oil of lemon eucalyptus [p-methane 3, 8-diol (PMD)] or IR3535 according to the instructions on the product label. DEET products should not be used on infants under two months of age and should be used in concentrations of 30% or less on older children. Oil of lemon eucalyptus should not be used on children under three years of age.
• Clothing can help reduce mosquito bites: Wearing long sleeves, long pants, and socks when outdoors will help keep mosquitoes away from your skin.
• Mosquito-proof your home and drain standing water: Mosquitoes lay their eggs in standing water. They can begin to multiply in any puddle or standing water as small as a bottle cap that lasts for more than four days. If you have a bird bath in your yard, be sure to empty it daily and refill it with fresh water. Remove containers that may hold water in places that are hard to see such as under bushes, porches, decks, or stairs.
• Drill holes in the bottom of recycling containers that are left outdoors so that water can drain out.
• Clean clogged roof gutters; remove leaves and debris that may prevent drainage of rainwater.
• Turn over plastic wading pools and wheelbarrows when not in use.
• Change the water in birdbaths every few days; aerate ornamental ponds or stock them with fish.
• Install or repair screens: Keep mosquitoes outside by having tightly fitting screens on all of your windows and doors.

For more info on local mosquito safety, visit the Massachusetts Department of Public Health.

Five Facts About Mosquitoes

1. They can lay eggs in as little as a teaspoon of stagnant water.
2. They can carry illnesses that can transmit to humans, such as eastern equine encephalitis and West Nile virus.
3. Mosquitoes are most active between dusk and dawn. Be sure to wear long clothing and insect repellent during that time.
4. There are over 150 species of mosquito in North America!
5. Mosquito bites itch because your body's immune system is reacting to the mosquito's saliva.