A hospital patient is being tested for suspected rabies.
It is not clear if the patient is a man or a woman, or from what age group.
The Public Health Agency (PHA) confirmed the person had recently travelled in an area affected by the disease, but where that was is also not known.
The patient is being assessed in accordance with the "national risk assessment protocol", the PHA added.
A PHA spokeswoman said: "The patient is currently being treated in the Royal Victoria Hospital, Belfast, and is being tested for a number of diseases including rabies."
She said there was no increased risk to the wider community.
There was no indication of the condition of the patient.
Rabies is a deadly viral infection of the central nervous system.
Its scientific name is hydrophobia, as those affected develop an irrational fear of water.
Transmission is generally through the bite or scratch of an infected animal, usually dogs, but also cats, bats and other wildlife.
It is characterised by animals 'foaming at the mouth' and once symptoms appear it is almost invariably fatal to humans.
The PHA stressed that a course of rabies vaccination could prevent infection.
Northern Ireland animal lover Lisa McMurray died from rabies at the Royal Victoria Hospital in 2009.
It is thought she contracted the disease after being bitten by a monkey at an animal sanctuary in South Africa, where she had gone to work as a carer in 2006.
Doctors also thought it was possible she may have been scratched by a dog.
Friends said that Lisa had sent emails detailing how she had been hurt when separating two fighting dogs.
She said one of the dogs, which was later put down by the sanctuary's owner, had been foaming at the mouth. A close friend said at the time: "Lisa was not a big fan of Christmas, because her parents were no longer here and that's why she went away.
"She just loved animals and just wanted to work with them.
"Lisa mentioned in her correspondence that she had been scratched by a dog, but she never mentioned being bitten by a monkey."
Lisa, who was also a member of the Cats Protection League, made a second visit to the South African animal sanctuary in 2008. After she had been back in Belfast for a few months she started feeling unwell. She was initially treated at the Ulster Hospital in Dundonald before being transferred to the Royal.
Friends also said that during her last visit to the animal sanctuary, dozens of monkeys had died from a virus.
Rabies is extremely rare in the UK - there have been only 23 cases since 1946, the last in 2009, and all infections were acquired abroad.
The last case of human rabies involving a dog bite suffered in the UK was more than a century ago in 1902.
Rabies is a notifiable disease in Northern Ireland, meaning that there is a legal requirement to report it to the authorities.