Former Democratic Sen. Kay Hagan, who had been ill for years due to a tick-borne illness that caused brain inflammation, died Monday at 66.

Hagan, a moderate Democrat who represented North Carolina, beat powerful incumbent Republican Elizabeth Dole to win her seat in 2008, before losing to Sen. Thom Tillis, R-N.C., in 2014. Colleagues and family honored her service in statements on Monday.

"We are heartbroken to share that Kay left us unexpectedly this morning," her family said in a statement, according to the Charlotte Observer. "Kay meant everything to us, and we were honored to share her with the people of North Carolina whom she cared for and fought for so passionately as an elected official. Most of all, we already miss her humor and spirit as the hub of our family, a role she loved more than anything. Nobody could light up a room and make people feel welcome like Kay."

Hagan was hospitalized in 2016 with encephalitis, or swelling of the brain. A family spokeswoman described the cause as a virus that's spread by ticks from animals to humans, citing a doctor who had been treating her. Test results indicated Hagan contracted what's known as the Powassan virus.

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Hagan's recovery was slow, though her family said she had improved significantly. In mid-2017 her family said she “clearly understands what people say to her and recognizes her friends when they come to visit."

Earlier this year, Hagan made a public appearance at the groundbreaking of a control tower at an airport in Greensboro for which she helped secure funding during her time in office.

Sen. Richard Burr, R-N.C., issued a statement on Hagan's passing Monday.

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“Brooke and I are deeply saddened by the sudden and untimely loss of Kay Hagan," he said. "Kay dedicated much of her life to serving North Carolina, and she will be remembered for her tireless work on behalf of the home and the people she loved. In our time as Senate colleagues, we worked across the aisle together frequently on issues that we both knew would determine what type of country our children would inherit, from conservation to our common defense. She tackled everything she did with a passion and a sense of humor that will be missed. Our thoughts and prayers are with her family.”

The Greensboro Democrat, who served in the Senate for six years, lost her seat in 2014 to Tillis.

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"Susan and I are absolutely heartbroken by Senator Kay Hagan’s sudden passing and we extend our condolences and prayers to her loving family and many friends," Tillis said Monday. "We join all North Carolinians in remembering her dedicated and distinguished record of public service to our state and nation."

During her time in office, Hagan served on the committees for Armed Services; Health, Education, Labor and Pensions; Small Business and Entrepreneurship; and Banking, Housing and Urban Affairs. She chaired the Armed Services Subcommittee on Emerging Threats and Capabilities and the HELP Subcommittee on Children and Families, according to her government biography.

Hagan advocated for deficit reduction and her state's agricultural industry while still voting with Democrats on major legislation including the Affordable Care Act, known as Obamacare, and the American Recovery and Reinvestment Act, known as the stimulus package.

The Associated Press contributed to this report.