(CNN) -- For the first time, a worker with the World Health Organization has fallen ill from Ebola, the WHO told CNN on Sunday.
The health worker is in Sierra Leone and is receiving care, the WHO said. No further details were given immediately.
Separately, a British citizen infected with the virus in Sierra Leone is being flown home, the British Department of Health announced Sunday.
The man, simply identified as William, lives in the West African nation in a home established by an American university for researchers.
He is a volunteer nurse in Kenema Government Hospital, where he was working with Ebola patients, according to Dr. Robert Garry of Tulane University.
Garry is manager of the university's program that researches Ebola. The hospital is run by the government of Sierra Leone, but receives support from Tulane researchers.
The UK government said a specially equipped C17 Royal Air Force plane would transport the patient, who would be transferred to an isolation unit at the Royal Free London NHS Foundation Trust.
"UK hospitals have a proven record of dealing with imported infectious diseases and this patient will be isolated and will receive the best care possible," said deputy chief medical officer John Watson in a press release.
Meanwhile, Ivory Coast announced Saturday that it's closing its borders in response to the Ebola outbreak in West Africa.
Prime Minister Daniel Duncan signed the order that closes the land borders Ivory Coast shares with Guinea and Liberia.
The borders will remain closed until further notice in an effort to prevent the Ebola virus from spreading into its territory, according to the government statement.
Ebola is one of the world's most virulent diseases, according to the WHO.
The virus is introduced to human populations through the human handling of infected animals -- like fruit bats, gorillas and monkeys, to name a few -- found sick or dying in the rainforest.
The infection is then transmitted among humans through direct contact with the blood or other bodily fluids of infected people.
WHO's maps of confirmed cases show the Ebola outbreak is limited to four West African nations -- Liberia, Sierra Leone, Guinea and Nigeria. So far, nearly 2,500 suspected cases have been reported in what the WHO says is the worst known outbreak of the disease.
However, the WHO's website says the survival rate for people with Ebola in this outbreak has been 47%, which is a substantial improvement over the disease's survival rate, historically.