On alert for EEE, West Nile

Health officials in communities south of Boston are urging people to take these common-sense precautions because mosquito samples from Southeastern Massachusetts have tested positive for West Nile virus and Eastern equine encephalitis in recent weeks.

This also happens to be the time of year when routine mosquito-spraying efforts wind down for the season. The insecticide that is used to kill adult mosquitoes is effective only in temperatures above 50 degrees, and because it often gets colder than that at night now, most local authorities have suspended their spraying.

“But it doesn’t mean the risk is gone,’’ said John J. Smith, director of the Norfolk County Mosquito Control Project. The Norwood-based organization serves 25 communities, and stopped its ground spraying program on Sept. 11.

Until the weather gets colder, and frost sets in, mosquito-borne illnesses will remain a concern.

“It makes me nervous,’’ said Smith. “It’s hugely important that people be paying attention right now, because there is triple-E in Massachusetts.’’

There is no treatment for EEE or West Nile virus, according to the state Department of Public Health.

Most people who become infected with the West Nile virus show no symptoms at all, and recover on their own. Others may experience fever, headache, nausea, and a skin rash on their chest, stomach, and back. People age 50 and older have a higher risk of developing severe illness, such as encephalitis or meningitis. Ten people in Massachusetts were infected by the virus over the past five years; one died from the disease.

EEE is more deadly, and its symptoms include a high fever, stiff neck, headache, and fatigue. The disease can progress quickly and ultimately result in swelling of the brain. Patients may go into a coma within a week; few recover completely, and survivors often have permanent disabilities.

Since EEE was first identified in Massachusetts in 1938, there have been fewer than 100 reported cases in the state - more than 60 percent of which originated in Plymouth and Norfolk counties. There was one human case of EEE in Massachusetts last year: A 73-year-old Essex County resident died on Oct. 26 after developing symptoms the month before while vacationing in Maine. Since 2004, 13 others were infected with EEE in the state - and six of them died.

There have been no human cases of either EEE or West Nile reported in Massachusetts this year as of Monday. But the public health department says it has detected EEE in mosquito samples from Easton, Freetown, Lakeville, Mattapoisett, Plympton, Raynham, and Rochester. The agency has also detected West Nile virus in mosquito samples from Freetown, Lakeville, Quincy, Walpole, and Wareham.

Last Friday, after the agency raised the alert level for mosquitoes in southeastern Massachusetts, the Greater New Bedford Regional Vocational-Technical High School canceled its sporting activities that weekend, and Freetown-Lakeville school officials suspended all evening outdoor activities.

The region has plenty of salt marshes, swamps, and lowlands - which are havens for mosquitoes. The rainy weather this summer has also exacerbated the mosquito problem, said Anthony Texeira, superintendent of the Plymouth County Mosquito Control Project.

“We have people calling up saying they have tons of mosquitoes,’’ said Texeira. Last year, the agency received 14,000 spraying requests from residents; this year it received 20,000 requests, he said.

The agency usually does its ground spraying before sunrise. Between 3 and 6 a.m., a truck equipped with a sprayer drives around spraying a pesticide containing sumithrin. The spray covers 300 feet in all directions, and kills flying mosquitoes in its path. The chemical breaks down in sunlight, explained Texeira.

“It’s not going to kill every mosquito; it’s just going to reduce the number. All we’re trying to do is reduce the risk,’’ said Texeira.

A synthetic pesticide, sumithrin has been registered with the Environmental Protection Agency since 1975. The EPA has determined that the chemical does not pose unreasonable risks to human health and most wildlife; however, it can be toxic to fish and to bees.

Residents who don’t want their property sprayed can ask to be put on a “no-spray’’ list - an option popular with people who have asthma or are sensitive to chemicals. To be placed on the list for the season, residents must send a certified letter to their town clerk by March 1. They must also mark their property every 50 feet with orange surveyor’s tape, to let the truck drivers know that the area is off-limits.

In recent weeks, Plymouth County Mosquito Control Project trucks have sprayed in Brockton, Carver, Marion, Mattapoisett, and Rochester. The schools and playgrounds in Middleborough and Plympton were scheduled to be sprayed earlier this week - on Monday and Tuesday.

Ball fields and playgrounds in Mattapoisett and Rochester were scheduled to be sprayed again today; tomorrow the grounds of the public schools in Mattapoisett, Marion, and Rochester will be treated. Texeira expected those to be the final spraying sessions of the season.

Texeira said he wants “to make people aware they have to use DEET-based repellent’’ to discourage mosquitoes from biting.

“That is far more effective than us spraying their property,’’ he said. “People really have to protect themselves. When you send your son off to football practice, give him some repellent.’’

More information is available about: The Plymouth County Mosquito Control Project at http://www.plymouthmosquito.com/.

The Norfolk County Mosquito Control Project at http://www.massnrc.org/ncmcp/.

The Department of Public Health’s literature on EEE and West Nile virus at http://www.mass.gov/dph/wnv.

Emily Sweeney can be reached at esweeney@globe.com.