A man in New York developed an extremely rare and fatal brain disorder after he ate squirrel brains, according to a new report of the man's case.

In 2015, the 61-year-old man was brought to a hospital in Rochester, New York, after experiencing a decline in his thinking abilities and losing touch with reality, the report said. The man had also lost the ability to walk on his own.

An MRI of the man's head revealed a striking finding: The brain scan looked similar to those seen in people with variant Creutzfeldt-Jakob disease (vCJD), a fatal brain condition caused by infectious proteins called prions. Only a few hundred cases of vCJD have ever been reported, and most were tied to consumption of contaminated beef in the United Kingdom in the 1980s and 1990s. (In cows, vCJD is commonly called "mad cow disease.")

But in this case, the man had another dietary habit that could have raised his risk for vCJD: His family said he liked to hunt, and it was reported that he had eaten squirrel brains, said Dr. Tara Chen, a medical resident at Rochester Regional Health and lead author of the report. It's unclear if the man consumed the entire squirrel brain or just squirrel meat that was contaminated with parts of squirrel brain, Chen said. [27 Oddest Medical Cases]

Chen didn't treat the patient, but she uncovered the case while writing a report on suspected Creutzfeldt-Jakob disease cases seen at her hospital in the last five years.

The report was presented on Oct. 4 at IDWeek, a meeting of several organizations focused on infectious diseases.

A rare brain disorder

Creutzfeldt-Jakob disease (CJD) is a progressive neurological disorder that affects only about 1 in a million people each year worldwide, according to the National Institutes of Health (NIH). It's a "debilitating disease" that progresses quickly and usually results in death within one year of diagnosis, Chen told Live Science. There is no treatment or cure.

The disease results from prion proteins that fold abnormally, leading to lesions in the brain.

There are three forms of Creutzfeldt-Jakob disease (CJD): one that is inherited, one that comes from exposure to infected tissue from the brain or nervous system (this form includes vCJD), and one type that is "sporadic" and does not appear to have a genetic or environmental cause.

The sporadic type is the most common, responsible for 85 percent of cases, according to the NIH.

Because CJD is so rare, doctors at Rochester Regional Health were surprised when four suspected cases of the disease occurred at the hospital within a six-month period, from November of 2017 to April of 2018. That number is higher than expected based on the population of the Rochester area, which has about 1 million people, said study co-author Dr. John Hanna, also a medical resident at Rochester Regional Health.

This high number of suspected CJD cases prompted Chen, Hanna and colleagues to conduct a review of suspected CJD cases occurring at their hospital from 2013 to 2018. (Five cases were identified, but two of those five ultimately tested negative for CJD.)

That's when the doctors came across the case tied to squirrel brains. Tests indicated that this was a "probable" case of vCJD because of the MRI finding and a test that showed specific proteins in the patient's cerebrospinal fluid, which often indicate the disease.

However, CJD can be confirmed only with a test of brain tissue on autopsy at death. Although the patient passed away after his diagnosis, Chen and colleagues are working to obtain access to his medical records to see if CJD was confirmed at autopsy. If so, such a confirmation would be highly unusual; only four confirmed cases of vCJD have ever been reported in the United States, according to the Centers for Disease Control and Prevention.

The review of the five cases revealed a concerning finding: Diagnosis of the condition was often delayed; in one case, about two weeks passed before doctors suspected that a patient had CJD. In that case, the patient, a 65-year-old woman, had undergone plasmapheresis, a blood-filtering procedure, and a gynecological surgery before her diagnosis.

Quick diagnosis of CJD is important, because infectious prions could contaminate equipment used on patients with the disease, and this might transmit the condition to others if the equipment is not properly cleaned.

Diagnosis may be delayed, in part, because CJD is rare and is not "on the tip of the physician's mind" when assessing a patient, Hanna told Live Science. In addition, once doctors suspect CJD and order a cerebrospinal fluid test, it typically takes around two weeks to get the test results.

The report highlights the need for doctors to keep CJD diagnosis in mind and for hospitals to have "policies for infection control when it comes to CJD," Hanna said.

Originally published on Live Science.