A UN staff member in Sierra Leone has died of Ebola, the third employee to succumb to the deadly virus, the organisation has said.

A statement by UN Women said Edmund Bangura-Sesay, a local driver for their office in Sierra Leone, died on Saturday.

The statement said Bangura-Sesay was quarantined last Tuesday after his wife showed symptoms. It said his wife remained under treatment, and that the UN was working to make sure that everyone who came into contact with Bangura-Sesay while he had symptoms was assessed and quarantined.

A Sudanese UN medical official who caught Ebola while working in Liberia died last week in a German hospital. The volunteer medic was the second member of the UN mission, known as UNMIL, to contract and succumb to the virus.

In total, more than 4,500 people have died and nearly 10,000 have been infected with the hemorrhagic fever, most of them in West Africa, since the start of the year.

On Monday, the US issued stringent new protocols for health workers treating Ebola victims, directing medical teams to wear protective gear that leaves no skin or hair exposed when caring for patients infected with the virus.

Under the new protocols, Ebola healthcare workers must undergo special training and demonstrate competency in using protective equipment designed to prevent their exposure. Use of the gear, now including coveralls, and single-use, disposable hoods, must be overseen by a supervisor to ensure proper procedures are followed.

'Nigeria Ebola-free'

Health officials have warned that the Ebola outbreak could escalate and become a global threat if efforts to contain the virus are not stepped up.

Positive news emerged, however, earlier on Monday as the World Health Organisation (WHO) declared Nigeria Ebola-free, after a 42 day period with no new cases.

Al Jazeera's Haru Mutasa, reporting from Abuja, said the news had been welcomed by Nigerians.

"The average Nigerian is relieved ... a lot of people have been quite scared. Officials want people to celebrate but to remain cautious.

"Nigeria is a transport hub, and the virus can be brought back, and this is why officials are not taking any chances," Mutasa said.

Nigeria was the second country in West Africa to be declared Ebola free in the past week. On Friday, the UN health agency declared Senegal free of Ebola after it passed the 42 day landmark.