Stay on Guard Against Mosquitoes

It's interrupted picnics, delayed flights and washed out ball games. But this summer's wet weather has also triggered a boom in the local mosquito population, which in turn has elevated the risk of mosquito-borne illnesses like West Nile Virus and Eastern Equine Encephalitis.

No human cases of West Nile or EEE have been reported in Massachusetts so far this year, but 39 mosquito pools and 26 dead birds have tested positive for West Nile Virus—including a bird found in Sudbury, according to the state department of public health. The department also announced on Monday the summer's first report of a mosquito infected with EEE, which was found in Carver.

In its Monday statement, department officials cited an increased incidence of West Nile-positive mosquito activity in the greater Boston and Worcester areas. Though the risk to humans of contracting EEE is low, the risk of contracting WNV is high, according to the announcement, which emphasized the need for residents to take preventive action.

“It has been a really wet summer, and what this has done is really increase the population of mosquitoes that carry West Nile,” said Donna Rheaume, spokesperson for the department. “So we really want to stress that residents take precautions by using repellents and removing pools of standing water from their property if possible, because that's where mosquitoes like to breed. From a public health perspective it's really critical.”

And although many think of mosquitoes as a summertime phenomenon, the tiny tormentors will continue to thrive well into football season. In fact, all six of the human cases of West Nile diagnosed in Massachusetts last year occurred between August 14 and September 27.

“The good news is that we haven't had a human case yet this year, but we're not out of the woods,” Rheaume said. “We have seen cases in the fall, after Labor Day. We typically say there's a risk right up until the first hard frost, when all the mosquitoes die. That's particularly important this year, because of all the rain we've had.”

West Nile Virus can affect anyone, but individuals over age 50 are thought to have an elevated risk. The most effective way to avoid developing a mosquito-borne illness is to avoid mosquito bites. This starts with limiting outdoor activity between the hours of dusk and dawn, when mosquitoes are most active. Wearing long sleeves, long pants and socks can help protect the skin, but health officials also urge residents to use insect repellents.

“The easiest way and what we think is a very effective way for people to protect themselves is with repellents,” Rheaume said. “Using repellents really is one of the best things that we recommend. And there are a lot of options. We know that DEET's very effective, but there are alternatives for people who would prefer not to use DEET.”

Government health officials recommend the use of a repellent containing DEET (N,N-diethyl-meta-toluamide), picaridin, permethrin, IR3535 (the active ingredient in repellents marketed by Avon), or oil of lemon eucalyptus (the only recommended repellent that is plant-based rather than chemical). Those with small children should note that DEET should not be used on infants younger than two months and should be used in concentrations of 30 percent or lower in older children. Oil of lemon eucalyptus is not recommended for children under the age of three.

Athletes gearing up for fall sports may want to apply repellents more frequently than others, and not only because most repellents wash away with sweat. Studies also show that mosquitoes are particularly attracted to an elevated body temperature, carbon dioxide in exhaled breath, and skin chemicals including lactic acid—all factors that intensify during exercise.

The other way to reduce the risk of mosquito-borne illness is to reduce the number of mosquitoes by providing them with fewer places to breed. This means minimizing the number of places where water can collect and sit following a period of rain.

“If there's a tire or pool cover or birdbath where there's standing water, those are things to really get rid of,” Rheaume said.

For more information about mosquito-borne illnesses, visit www.mass.gov/dph/wnv