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State steps up aerial mosquito spraying

By Matt Woolbright
Globe Correspondent / June 8, 2012
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Aerial mosquito spraying could occur earlier and more often this year, as a result of new state guidelines for battling Eastern equine encephalitis.

An expert panel — convened ­after the state was criticized for not proactively spraying mosquito-­killing pesticides last summer — concluded that Eastern equine encephalitis is an annual risk for Massachusetts residents. The findings led the state Department of Public Health to ­announce this week that it will lower the threshold for considering when to spray and will research new spraying tactics to target disease-bearing mosquitoes.

Last summer, two cases of Eastern equine encephalitis were contracted in Southeastern Massachusetts, one of them fatal.

“EEE and other mosquito-borne illnesses represent a serious public health concern for Massachusetts families,” John Auerbach, commissioner of public health, said in a statement. “These revised guidelines will ensure that we mount the most effective science-based approach to reduce the risk of disease spread by mosquitoes among our residents.”

The creation of the panel, which included specialists from around the country, was prompted by an outcry from several health agents in towns across Southeastern Massachusetts. In December, they sent a joint letter to Auerbach, urging more aerial spraying and asking that the region be considered to be at high risk for Eastern equine encephalitis. None of the health agents could be reached Thursday.

Members of the panel agreed that the disease has evolved from occurring sporadically, with some years of no cases, into an annual event.

“I think EEE is out there every summer,” said Dr. Richard Pollack, a Harvard instructor and chairman of the mosquito advisory group. “Sometimes we’ve just gotten lucky and not had any ­humans infected.”

Testing for infected mosquitoes will begin in June. The tests almost never detect an infected mosquito before July, said Kevin Cranston, director of the Bureau of Infectious Disease for the Department of Public Health.

The peak of the dangerous season is mid-August, and the disease-bearing insects usually die off by early September, Cranston said.

Under the new guidelines, the department will begin considering aerial pesticide spraying after a single mammal-biting infected mosquito is found. Previously, discussions on whether to spray took place after two EEE-infected mosquitoes were found.

In addition, the risk level will be elevated to critical if one human case is confirmed, rather than two. The department also said it would work to develop better tactics to target focal spots and strategies for more rapid aerial sprayings.

The pesticides do pose some risks, Cranston acknowledged. When a spraying is scheduled, the department encourages residents to stay inside, close their windows, and turn off air conditioning units.

“Only when there is a public health emergency and a human is at a high risk will we consider such a drastic measure,” said Cranston, who said the least dangerous, yet still effective, chemical combination was chosen as the pesticide.

Immediately after spraying, health officials say, populations of the most dangerous species of mosquitoes are usually diminished by 50 percent.

It is unknown how prevalent the mosquitoes will be this year.

Pollack said that their short life-span makes predictions of population and degree of infection impos­sible.

“We have to monitor things constantly and make decisions on an ad hoc basis,” he said.

Eastern equine encephalitis attacks the brain and nervous system. About two-thirds of people ­infected either die or are permanently disabled, Cranston said. There is no treatment for the disease, which has taken seven lives in Massachusetts since 2004.

“Our job is to alter the risk in the environment,” Cranston said.

Even with the spraying, personal protection is the best prevention, Cranston said. He advised people to wear repellent with DEET; to stay indoors at dawn or dusk, when mosquitoes are most active; and to eliminate standing water near homes.

Matt Woolbright can be reached at Follow him on Twitter ­@reportermatt.

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