Blood tests are expected to be made public today which will reveal whether a man in Belfast has contracted Ebola.
The unidentified patient, who recently travelled to West Africa, has been quarantined in the city's Royal Victoria Hospital since Friday.
He has already tested positive for malaria.
The current Ebola outbreak has claimed more than 4,500 lives so far, mostly in Africa.
Professor Bill Tormey, a consultant in Beaumont Hospital in Dublin, says the virus is particularly hard to diagnose.
He said: "It gets into the blood and it starts this cascade of using up the proteins that cause clotting, so your blood starts to leak out of your blood vessel.
"You go into renal failure, liver failure, you start to cough, your lungs stop working and before that it causes the tired fever and headaches which mimic things like the flu, malaria and a while lot of other diseases."