'It's critical that residents protect themselves from mosquito bites,' said a Massachusetts health official. 'Mosquitoes will be biting until the first frost.'

The two became ill with the dangerous Eastern equine encephalitis virus, known as EEE, within days of a third woman who also lives nearby. She remains hospitalized in serious condition, officials said.

Four New Hampshire residents have also turned up ill with the virus in recent weeks; none have died.

Ward Off Mosquitoes

It wasn't clear how or when the disease was contracted by the 5-year-old girl and the 83-year-old man, who lived in the state's southeastern arm, said Dr. Al DeMaria, state director of communicable disease control.

He released few other details and declined to identify the two by name, citing privacy concerns. "Obviously this is a horrendous situation for these families," he said.

Officials advised residents to try to ward off mosquitoes.

"It's critical that residents protect themselves from mosquito bites," DeMaria said. "Mosquitoes will be biting until the first frost."

Kills Around 35 Percent

The United States has had only about 200 confirmed cases of EEE since 1964, according to the federal Centers for Disease Control and Prevention. The disease kills around 35 percent of the people who contract it, and causes mild to severe neurological problems in another 35 percent.

Symptoms range from mild flu-like illness to inflammation of the brain, coma and death. There is no licensed vaccine for humans. The virus also can affect birds and horses.

The girl, from Halifax, became ill Aug. 26 and died Sept. 4; lab tests later identified the disease, although results of a final test are pending. The man, from Kingston, became ill Aug. 21 and died five days later. Tests confirmed the disease a week after he died.

The 63-year-old Duxbury woman became ill Aug. 26.

Last year, Massachusetts had four confirmed human EEE cases, two of them fatal. Massachusetts is among the states that has had the largest number of cases; others are Florida, Georgia, and New Jersey.

As of last week, the state had tested around 120,000 mosquitos for EEE, and only 15 tested positive for the virus.