Charlene Manseau, 63, of Amesbury died of Eastern equine encephalitis Saturday and her family wants other cancer survivors to take extra precautions against the mosquito-borne illness.

Manseau is the second fatal case of EEE in Massachusetts this year. State health officials reported earlier this month that a Westborough man in his 70s had died from the disease.

Becky Manseau Barnett said her mother’s cancer treatments may have weakened her immune system, making her more susceptible to the virus.

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“Immunosuprression could have contributed to her having severe symptoms with the EEE,” Manseau Barnett, 33, said in an interview Monday.

State health officials on Monday said there had been a second EEE death, though for confidentiality reasons did not confirm the victim’s identity. The Massachusetts Department of Public Health confirmed Thursday that an Amesbury woman in her 60s had been hospitalized with the disease.

The agency also announced Monday that a Plymouth County resident, described as a male under age 18, has been diagnosed with EEE—the seventh human case of EEE reported in Massachusetts this year. Last year, just two cases and one death were reported. The Plymouth County patient was not hospitalized and is recovering, the state said.

Based on the new case, the state raised the threat level for EEE to “critical” in Marshfield and “high” in Scituate—meaning the state is urging those communities to cancel all outdoor events in the evening, when mosquitoes are active, until the first hard frost.

Benjamin Duce, 79, of Westborough, a former research scientist and US Army veteran died in August from EEE, his family said. Duce was in a coma for the last four days of his life and an autopsy confirmed the cause of his illness was EEE.

Health officials also disclosed two additional human cases of West Nile virus, another mosquito-borne illness that is less severe than EEE. The new cases were reported in a Boston resident in his 50s, who has been hospitalized, and a Hampden Country resident in his 50s who was hospitalized but has since been discharged.

There have now been 19 human cases of West Nile in Massachusetts this year, and one death. Last year there were six human cases.

“Summer may be over but the threat of mosquito-borne illness is not—we can expect to continue seeing mosquito activity until the first hard overnight frost,” state epidemiologist Dr. Al DeMaria said in a statement. “People need to continue to use insect repellant, cover up exposed skin, and avoid being outdoors at dusk and after nightfall when mosquitoes are at their most active.”

Manseau Barnett said her mother started experiencing headaches, fever, nausea, and vomiting early last week. Manseau was disoriented Wednesday and her husband took her to the emergency room at Anna Jacques Hospital in Newburyport. She was transported to Brigham and Women’s Hospital that same day.

“It wasn’t confirmed it was EEE until Wednesday,” she said. “The initial test for EEE came back negative.”

Manseau Barnett said the doctors told her that the false negative could have been a result of her mother’s history with cancer.

Manseau had uterine cancer five years ago and recently was diagnosed with lymphoma. She had been in remission for a year and was receiving Rituxan infusions every other month to extend the length of her remission, Manseau Barnett said.

Amesbury Regional Health Director John Morris said efforts to eradicate mosquitoes began quickly last week. “When we were notified that we had a human case of EEE we immediately ordered a spray of the whole city,” he said.

Northeast Mosquito Control sprayed Amesbury for mosquitoes on Thursday and Friday, he said.

Amesbury Mayor, Thatcher W. Kezer III, issued an order to ban all outdoor activities on city property between the hours of 5 p.m. and 9 a.m. until further notice, Morris said.

“Most people seem to be compliant with that and seem to be able to work that into their schedules,” he said.

Mosquito control officials will conduct another round of tests of mosquitoes throughout Amesbury this week. Morris said his office should receive the results of those tests by Friday afternoon and will then re-evaluate its EEE prevention measures.

EEE is transmitted to humans through the bite of an infected mosquito.

The Centers for Disease Control and prevention reports that EEE has a 33 percent mortality rate and that most survivors suffer significant brain damage.

Manseau Barnett said her mother was a nurse at Anna Jacques Hospital for 40 years and had retired last year.

Her parents planned to celebrate their 41st wedding anniversary next week, she said.

“She and my father were very devoted to each other,” she said.

Manseau was “very committed” to her four children and twelve grandchildren and loved to garden and cook, Manseau Barnett said.

“She made all kinds of clothes for us growing up,” she said. “She loved to sew and do crafts.”

Manseau Barnett and her siblings grew up in Newburport and her parents moved to Amesbury’s Lake Attitash in 2005.

Manseau Barnett described her mother as “a woman of deep faith” and said she was very involved at Hope Community Church in Newburyport.