A British national living in Sierra Leone has tested positive for Ebola, the UK department of health said.
It is the first confirmed case of a Briton contracting the deadly virus during the recent outbreak. There is no cure for Ebola.
Professor John Watson, deputy chief medical officer, said: "The overall risk to the public in the UK continues to be very low. Medical experts are currently assessing the situation in Sierra Leone to ensure that appropriate care is provided.
"We have robust, well-developed and well-tested NHS systems for managing unusual infectious diseases when they arise, supported by a wide range of experts."
The World Health Organisation (WHO) has put the number of people infected with the deadly virus at 2,615. Some 1,427 have died since the disease was identified in Guinea in March and spread to Sierra Leone, Liberia and Nigeria.
It was confirmed last week that an Irish engineer who died at his Donegal home after returning from Sierra Leone had not contracted Ebola.
Dessie Quinn (43) was being treated for malaria after returning two weeks ago from the west African country and was found dead in bed by a friend.
The Health Service Executive said test samples had proved negative for Ebola.
The virus has no cure and rigorous quarantine measures are used to stop its spread, as well as high standards of hygiene for anyone who might come into contact with sufferers.