The virus has infected seven people in the state this year and killed two. On Monday, a 7-year-old Marshfield boy with a bug bite was diagnosed with the disease.

The state Department of Public Health has blanketed 21 communities south of Boston with pesticide to prevent mosquitoes from spreading EEE, which kills more than 30 percent of humans who contract the disease and is at its highest level in three decades in Massachusetts.

“Aerial spraying is an unusual event and one we only recommend when the risk to human beings warrants it,” said Kevin Cranston, director of the state health department’s Bureau of Infectious Disease.

Environmentalists, organic farmers, and wildlife specialists say they are as sensitive as others to the public health threat posed by mosquitoes carrying the EEE or West Nile viruses. But state health officials should find a smarter solution than spraying pesticide from planes, they say.

From the epicenter of the EEE outbreak, Easton resident Kyla Bennett, director of the New England chapter of Public Employees for Environmental Responsibility, wants to know if the state made real headway by dumping pesticide on 478,308 acres in Southeastern Massachusetts, including her home and garden. Some communities, including Bridgewater, Easton, Norton, Raynham, Taunton, and West Bridgewater, were sprayed twice.

“I understand we are facing an extremely serious problem with mosquitoes causing illness and death, and that is an absolute tragedy,” she said in an interview.

“People see relatives or friends getting West Nile or EEE and dying. But what they don’t see is the long-term impact in 20 years of spraying these toxins that are getting in our water and on our vegetables,” she said.

Officials have repeatedly said the state’s chosen product, Anvil 10 + 10, a combination of sumithrin and piperonylbutoxide, has very low toxicity to humans and animals and breaks down rapidly in sunlight. It has proven itself a useful tool, they say.

“Following aerial spraying, we have seen a significant reduction in the volume of mosquitoes,” Public Health Commissioner John Auerbach said in a press release about a week after the July 20-22 operation. He said it wiped out approximately 60 percent of the mosquitoes in the areas hit.

But Bennett, a biologist and attorney formerly with the US Environmental Protection Agency, said the application of logic — not plane-delivered pesticide — is a necessary first step in dealing with a health scare. Aerial spraying may not be the smartest approach, said Bennett, who has a doctorate in ecology and evolutionary biology. She said pesticide droplets dispensed from a plane do not land on mosquitoes accurately, citing several studies that show mortality rates of 34 percent or below — even as low as zero — for mosquito populations in vegetated areas.

Aerial spraying targets only flying adults, not the eggs, larvae, or pupae, which means mosquito control lasts a week at most, she said.

“We should be working our butts off to find an alternative solution. I think the mosquito problem is only going to get worse. There has to be a better way than spraying,” she said.

According to Cranston, the Department of Public Health found high EEE infection rates among mosquitoes in southeastern Massachusetts appearing much earlier than in previous years. Since most mammal-biting mosquitoes live from spring until late summer, and can fly from 2 to 9 miles in search of nightly blood meals — typically from birds, horses, or humans — health officials anticipated a high risk of virus transmission to humans, he said.

Aerial spraying only has a transient impact on the mosquito population, but health officials use it to interrupt the life cycle, he said, adding the approach was a proactive response to signals of looming trouble. “This year turned out to be very bad. It is one of the worst years in the decade,” he said, adding state data show “you can reasonably say the spray helped drop the infection rate.”

A minimal-risk pesticide is effective when sprayed, as it was, with a low-volume, ultra-fine mist at night to hit mosquitoes and not “non-target” insects, such as honey bees. The state compared mosquito trapping data from before and after the aerial spray, he said, calculating the kill rate at about 60 percent.