Mosquito Season is Upon Us!

Mosquitoes are most active in Massachusetts from June through August, but the true determination of mosquito activity is weather dependent.

Most adult mosquitoes can be found during the day in damp, shady areas where they can find protection from the sun.  Mosquitoes can spread diseases that may make humans and animals sick. Viruses carried by mosquitos can be transmitted to humans or animals through a mosquito bite.

It is possible to be bitten at any time of day, as different kinds of mosquitoes are active at different hours. Most mosquitoes are active from just before dusk, through the night until dawn.

West Nile Virus (WNV) and Eastern Equine Encephalitis (EEE or Triple E) are viruses that occur in Massachusetts and can cause illness ranging from a mild fever to more serious diseases like encephalitis or meningitis. There are also other diseases spread by mosquitoes that people may be exposed to when traveling to other regions of the world.

What is Eastern Equine Encephalitis?

Eastern Equine Encephalitis (EEE) is a rare but serious disease caused by a virus that is spread through the bite of an infected mosquito. In Massachusetts, the virus is most often identified in mosquitoes found in and around freshwater and hardwood swamps. EEE typically infects birds, often with no signs or symptoms.

Mosquitoes then become infected when they bite birds that were previously infected with the virus. The mosquito then transmits the disease to the human or animal they bite. Humans and other types of mammals such as horses and llamas can become infected, but do not spread the disease to others.

In the past, outbreaks of EEE tend to occur in Massachusetts every 10-20 years and typically last two to three years long. 2019 was the first year of the most recent cycle of EEE activity with 12 human cases and 6 deaths in Massachusetts. In 2019, the risk level for EEE transmission to humans reached a high and critical level in many Massachusetts communities. 2020 is expected to be another active EEE year.

On July 3, 2020, the Massachusetts Department of Public Health announced the EEE virus had been detected in mosquito samples collected from Orange, Massachusetts for the first time this 2020 season.

No human or animal case has been detected so far this season. The symptoms of EEE are fever (103 degrees F – 106 degrees F), stiff neck, headache, and lack of energy.

Symptoms show up three to ten days after a bite from an infected mosquito.

Inflammation and swelling of the brain, called encephalitis, is the most dangerous and serious complication of the virus. There is currently no treatment for EEE and those who survive the disease will often be permanently disabled. All ages can be affected, including children.

What is West Nile Virus?

West Nile Virus (WNV) is a mosquito carried virus that can cause illness ranging from a mild fever to more severe diseases like encephalitis or meningitis.

WNV is most commonly spread to people through the bite of an infected mosquito. The majority of people who are infected with WNV will have no symptoms. A small number of people who become infected will have symptoms such as fever, headache, body aches, nausea, vomiting, and sometimes swollen lymph glands. They may also develop a skin rash on the chest, stomach, and back.

Fewer than 1% may develop severe illness, including encephalitis or meningitis. These symptoms of severe illness can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness, and paralysis.

People older than 50 years of age have a higher risk of developing severe illness. There is currently no specific treatment for WNV infections. People with mild symptoms usually recover on their own and those with severe infections almost always require hospitalization. Neurological effects may be permanent.

How to Protect Yourself?

Only a small number of mosquitoes are infected at any given time, so being bitten by a mosquito does not mean you will get sick.

However, the best way to avoid mosquito-borne diseases is to prevent mosquito bites by taking the following proactive measures to better protect you, your family, and your neighbors:

  1. Mosquito Proof your Property – Limit the number of places around your home for mosquitoes to breed by eliminating sources of standing water or items that may hold water. Check rain gutters and drains, empty any unused flowerpots, wheel barrels, wading pools, change the water in birdbaths, and other water sources for animals frequently. Install or Repair Screens – Some mosquitoes like to come indoors. Keep them outside by having tightly-fitting screens on all windows and doors. Avoid turning on outdoor lights during peak mosquito activity.
  2. 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 evening or early morning. Otherwise, take extra care to use repellent and protective clothing.
  3. When Outdoors Wear Protective Clothing – Wear long pants, a long-sleeved shirt and socks. This may be difficult to do when the weather is hot, but it will help keep mosquitoes away from your skin. Mosquito netting may be used on baby carriages and playpens when small children are outdoors.
  4. Apply Insect Repellent any time you go Outdoors Use a repellent with DEET (N, N-diethyl-m-toluamide), permethrin, picaridin (KBR 3023), IR3535 or oil of lemon eucalyptus [p-methane 3, 8-diol (PMD)] 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.  Permethrin products are intended for use on items such as clothing, shoes, bed nets and camping gear and should not be applied to  
  5. Avoid Outdoor Areas with Obvious Mosquito Activity such as woods and wetlands.
  6. Animals and Pets – Keep animal or pet vaccinations and medications current. Speak to your veterinarian about mosquito repellents approved for use for animals and vaccinations to prevent EEE and WNV. Keep animals indoors or in screened-in areas during peak periods of mosquito activity.

The Bedford Board of Health will continue to work with the Massachusetts Department of Public Health and the Eastern Middlesex Mosquito Control Project (EMMCP) to monitor local mosquito populations for WNV and EEE.

To control mosquito larvae, each spring EMMCP conducts a helicopter application of biological larvicide to wetland areas in town and annually each summer the Bedford DPW treats catch basins in town. Additionally, based on acquired surveillance data from four mosquito trap locations in town, the EMMCP will continue with truck-mounted spraying events in Bedford to reduce populations of biting adult mosquitoes.

For More Information

Information about mosquito activity in Massachusetts during 2020 can be found on the Mosquito-borne Disease page on the MDPH website at

Facts sheets on WNV, EEE, and other mosquito-related materials are available by contacting the Bedford Board of Health at 781-275-6507 or by accessing the Board of Health website at

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