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Warm Humid Weather Ramps up Mosquito Population

August 07, 2019

If you’ve been outside recently you may have noticed that mosquitoes are out in full force.  While some mosquito bites will only itch, others can carry potentially dangerous illnesses. 

Some communities in Massachusetts have been put on warning as at high risk for mosquito-borne viruses.

Massachusetts Health Officials Label Some Local Communities as "High Risk"

Some communities in Worcester County and Southern Massachusetts have been put on warning as at high risk for mosquito-borne viruses. It's important for folks to take steps to avoid mosquito bites,” said Dr. Spence, chief of emergency medicine for Baystate Wing Hospital and Baystate Mary Lane Outpatient 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 (EEE) virus.  Most people won't experience symptoms from either virus, but there are important differences to be aware of.”

According to the Massachusetts Department of Public Health there are over 3000 different kinds of mosquitoes that have been 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 in order to lay their eggs. Many people don't realize the number of areas around their own house where mosquitoes can find the stagnant water they need.  All a female 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.

6 Tips to help protect yourself from mosquito-borne viruses

Dr. Spence 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:

1. 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.

2. 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.

3. Clothing can help reduce mosquito bites. Wearing long-sleeves, long pants and socks when outdoors will help keep mosquitoes away from your skin.

4. 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 that lasts for more than four days. If you have a bird bath in your yard, be sure to empty it daily and refill with fresh water.

5. Remove containers that may hold water in places that are hard to see such as under bushes, porches, decks, or stairs.

6. Install or repair screens. Keep mosquitoes outside by having tightly-fitting screens on all of your windows and doors. 

About West Nile Virus (WNV) and Eastern Equine Encephalitis (EEE)

EEE is relatively rare in humans, although there are occasional outbreaks in certain regions of the country. Fewer than 100 people have died from EEE in Massachusetts in the past 75 years, according to the Department of Public Health.  In the United States, approximately 5 to 10 EEE cases are reported annually. 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. Spence.  “The incubation period for the virus from the time of an infected mosquito bite to onset of illness ranges from four to 10 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. Spence.  “Severe illnesses are treated by supportive therapy, which may include hospitalization, respiratory support, IV fluids and prevention of other infections.”

West Nile virus (WNV) is a mosquito-carried virus most commonly spread to people through the bite of an infected mosquito.

The majority of people who are infected with WNV (approximately 80%) will have no symptoms,” said Dr. Spence.  “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. Spence.  “People with mild WNV infections usually recover on their own. People with severe WNV infections almost always require hospitalization.”

For more information about different types of mosquitoes that can spread disease, visit mass.gov