A government source in Sierra Leone said the World Health Organisation worker who contracted Ebola in the country was a Senegalese expert working for the WHO in the eastern town of Kailahun, Reuters news agency reported.
The WHO said it was the first time one of its healthcare workers had tested positive for the deadly virus.
As it reaches seven months since the Ebola outbreak started we take a look at the timeline of events leading up to the spread of the virus.
More than 100 British personnel are arriving in Sierra Leone to combat the Ebola outbreak in West Africa. Here's what else the UK is doing.
A man has been filmed helping an Ebola patient onto a plane without wearing any protective equipment.