A man is being treated in a Dublin hospital with what is believed to be the first case of variant CJD to originate in the Republic of Ireland.
One variant CJD case has previously been diagnosed in Ireland
He is said to be in a serious condition and further tests are expected to be carried out.
The patient is understood to be a man in his early 20s.
The hospital confirmed he never received a blood transfusion or made a blood donation.
The cause of infection is not linked to an operation, it said.
"There is a potential case of vCJD currently being investigated," said a hospital spokesman.
Creutzfeldt-Jakob disease (CJD) is one of a small group of fatal diseases caused by infectious agents called prions, which attack the brain.
New variant CJD (vCJD) is caused by exposure to bovine spongiform encephalopathy (BSE) and typically affects younger people.
Professor William Hall, chairman of the Irish Government's CJD Advisory Committee, said the public should not panic.
"The IBTS (Irish Blood Transfusion Service) has taken exemplary measures, I believe, to reduce the potential risk in the blood supply," he said.
"I would point out that the suspect case at the present time has never received blood, nor has donated blood."
The hospital spokesman said that in the interests of the patient and his family, no other details, including the name of the hospital, would be released.
It is understood the man has not lived in Britain, meaning that this is potentially the first case of variant CJD to originate in Ireland.
The Republic of Ireland already has strict restrictions on people who lived Britain between 1980 and 1996 from donating blood.
Only one variant CJD case has previously been diagnosed in the Irish Republic - a woman who had lived for some time in England.
Contaminated beef was the cause of most cases in the UK, but transfusion experts believe there is a potential for vCJD to be transmitted through blood or blood products.
The Irish Blood Transfusion Service (IBTS) recently announced new donor controls to reduce the risk of vCJD transmission in the country.