A New York man died after he developed a rare and fatal brain disorder from eating squirrel brains.

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.

Doctors discovered he developed a degenerative disease caused by the same infectious proteins that also result in the more infamous 'mad cow disease'.

However, it wasn't contaminated beef that caused this man's death. His family told doctors he enjoyed hunting and had recently eaten squirrel brains - although it's unclear if he ate the whole brain or squirrel meat contaminated with parts of the brain.

A 61-year-old New York man died in 2015 after he developed a rare and fatal brain disorder from eating squirrel brains (file image)

The findings of the report were presented on October 4 at IDWeek, an annual meeting of infectious diseases professionals, reported Live Science.

Lead author Dr Tara Chen, a medical resident at Rochester Regional Health, told the website she discovered the case while doing a report on cases of the disease seen at her hospital during a five-year period.

Creutzfeldt-Jakob disease (CJD) is a rare, degenerative brain disorder that is caused by coming into contact with tissue that has been infected, such as eating contaminated meat.

It is caused due to abnormal versions of a protein known as prion. Prions are normally harmless but, when misshapen, they become infectious and create lesions, according to the Mayo Clinic.

Symptoms include depression, anxiety, memory loss, personality changes, impaired thinking, difficulty swallowing and difficulty speaking.

The mental deterioration is rapid, usually occurring within a few months. Many sufferers lapse into coma.

Usually symptoms begin to appear around age 60 and approximately 70 percent of sufferers die within a year.

There is no treatment or cure for CJD. Treatment plans currently involve lessening the severity of symptoms and making those affected comfortable.

CJD occurs in three forms. One is sporadic with no known causes, which accounts for 85 percent of cases, according to the National Institutes of Health.

Another form is hereditary. Those with a family history of the disease and have a genetic mutation account for 10 to 15 percent of US cases.

The rarest form is acquired CJD, which is when the brain or nervous system tissue becomes infected through exposure - only causing one percent of cases.

A type of CJD called variant CJD (vCJD) can occur from eating infected beef. First described in 1996 in the UK, this beef is already infected with a disease that is similar called bovine spongiform encephalopathy, or 'mad cow disease'.

About one in a million people around the world become infected, with just 350 cases occurring annually in the US.

Doctors at Rochester Regional Health wrote in the report that they were shocked when four suspected cases of CJD were presented between November 2017 and April 2018 because the disorder is so rare.

According to co-author Dr John Hanna, a medical resident at Rochester Regional Health that number is high when just one million people live in the area.

This unusually high number caused the doctors to review all suspected CJD cases at the hospital between 2013 and 2018. They found five cases in total, but two of them turned out to be negative for the disease.

During this review, they found the case of the man who ate squirrel brains. An MRI and a test of his cerebrospinal fluid found the proteins tied to CJD, and it was determined he had the most severe form, vCJD.

The authors note that CJD is only confirmed by testing the brain tissue during an autopsy.

The team is currently working to obtain the patient's medical records to see if a coroner confirmed CJD upon his death.

According to the Centers for Disease Control and Prevention, there have only been four confirmed cases of vCJD ever been reported in the US.