In a case report, researchers said the 61-year-old was brought to Rochester Regional Health in 2015 saying he was having trouble thinking, he was losing touch with reality and he couldn't walk.
The patient was diagnosed with Creutzfeldt-Jakob, which is a degenerative disease of the brain, which triggers the destruction of cells.
The man's family told doctors he was an avid hunter and had recently eaten squirrel brains.
There are three forms of Creutzfeldt-Jakob disease (CJD) and one form, which includes vCJD, is caused by exposure to infected tissue from the brain or nervous system tissue.
The disease is similar to "mad cow disease", which causes tiny holes to fill the brain until the tissue looks like a sponge (which is where '"spongiform" comes from), according to the National Institutes of Health. It is believed that the man's habit of eating squirrel brains may have raised his risk for vCJD.
Rod Rosenstein Offers 'Forceful Defense' Of 'Appropriate' Russia Probe
And Rosenstein has wide discretion on what he releases to Congress, and whether he releases any of it publicly. But the story was subsequently updated to say it was not clear what the reaction was to the offer.
It is a sister disease of CJD, a similar condition which is nearly 100 times more common.
Most people who contract it only live around a year. Doctors in Kentucky put out a warning against eating squirrel brains in 1997 after 11 people were diagnosed in the state with the non-variant Creutzfeldt-Jakob Disease, according to the New York Times.
Usually symptoms begin to appear around age 60 and approximately 70 percent of sufferers die within a year.
Dr. Tara Chen came across the unusual case when she was tasked with doing a report on cases of CJD seen at the hospital over the last five years.
His case was one of several detailed by doctors from Rochester Regional Health, a major hospital network in the city.
The disease results from prion proteins that fold abnormally, leading to lesions in the brain.
Of the five cases detailed in their report, however, two were eventually confirmed not to be CJD after all. With many fatal brain diseases, such as Alzheimer's, doctors can only be sure of the diagnosis by examining the brain after death.