His daughters said in a statement that “Dad is no longer able to participate in public life as he used to.”

At the age of 74, zoologist Jack Hanna was diagnosed with dementia, which experts suspect to be Alzheimer’s disease.

The most typical cause of dementia in older persons, with many showing signs as early as their middle 60s, is Alzheimer’s disease.

Yesterday, Jack Hanna’s family broke the devastating news that the adored naturalist had dementia. According to the National Institute on Aging, experts have determined that 74-year-old Hanna has Alzheimer’s disease, an irreversible, degenerative brain condition that gradually destroys memory and thinking abilities.

His “health has worsened dramatically,” according to the statement, and “his condition has progressed more faster in the previous few months than any of us could have predicted.” Dad used to be able to participate in public life, where he was watched, studied, and joked with by people all over the world. Sadly, he can no longer do so.

The most typical cause of dementia in older persons, with many showing signs as early as their middle 60s, is Alzheimer’s disease. Up to 5.5 million Americans age 65 and older may have Alzheimer’s disease, according to estimates from the NIA.

Memory issues are typically one of the early symptoms of Alzheimer’s, according to the NIA, however symptoms might vary depending on the stage of the disease.

Additionally, those who have the illness may have trouble speaking clearly, have vision and spatial problems, have impaired reasoning or judgment, repeatedly ask the same questions, get lost frequently, or have trouble performing daily tasks like driving a car or making food.

Douglas Scharre, M.D., a neurologist at The Ohio State University Wexner Medical Center, says, “We like to diagnose people when they have moderate cognitive impairment; they can still conduct day-to-day activities but are having some trouble with memory or cognition.”

“We can begin treatment earlier to stop the disease from getting worse.”

According to Mary Catherine Lundquist, program coordinator at Care2Caregivers at the COPSA Institute for Alzheimer’s Disease and Related Disorders, if someone’s Alzheimer’s disease is progressing more quickly than expected, doctors will frequently perform testing to make sure they aren’t suffering from a different form of dementia, such as Lewy body dementia or frontotemporal dementia, which can be mistaken for Alzheimer’s.

It can also accelerate up due to other medical conditions like a history of stroke, a head injury, or an underlying cancer.

According to a statement, the Columbus Zoo and Aquarium in Ohio, where Hanna is still director emeritus, is “saddened” to learn of Hanna’s illness. Up until his retirement last year, Hanna worked there to promote worldwide conservation efforts and to introduce people to wildlife.

His daughters have begged for privacy at this time, but they also assure people that he still has a terrific sense of humor. “He still dresses in khakis at home, yes.”