Rev. Jesse Jackson fought for civil rights for almost six decades, worked alongside Martin Luther King Jr. and formed Chicago’s Rainbow PUSH Coalition, among many other accomplishments. Now, the longtime activist is battling Parkinson’s disease, a neurodegenerative disorder that affects nearly one million Americans, reports NBC Chicago.

Jackson disclosed his diagnosis in a letter to friends and supporters. According to the 76-year-old community leader, he and his family started noticing changes in his physical capabilities about three years ago. As it became more difficult to accomplish tasks, he finally visited the doctor.

“After a battery of tests, my physicians identified the issue as Parkinson’s disease, a disease that bested my father,” Jackson wrote. “Recognition of the effect of this disease on me has been painful, and I have been slow to grasp the gravity of it.”

Despite his diagnosis, Jackson said he has no plans to quit working. He plans to undergo physical therapy and implement lifestyle changes to slow progression of the disease.

“I will continue to try to instill hope in the hopeless, expand our democracy to the disenfranchised and free innocent prisoners around the world,” he stated. “I’m also spending some time working on my memoir so I can share with others the lessons I have learned in my life of public service. I steadfastly affirm that I would rather wear out than rust out.”

Jackson concluded his letter with the call to action “Keep hope alive!”

Click here to learn more about Parkinson’s disease.