A British person living in Sierra Leone has tested positive for the deadly Ebola virus, in the first confirmed case for a UK citizen.
The Department for Health confirmed that the victim had tested positive.
But it was not known whether they were working out there treating patients, or living permanently in the former British colony.
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."
On August 12 a Spanish missionary, 75-year-old Miguel Pajares, became the first European victim of the disease.
Since then there have been dozens of false alarms in Ireland, Austria, Spain and Germany. In Germany, about 600 people were quarantined for two hours in a Berlin jobcentre after a false alarm about a suspected case of Ebola.
Two American doctors who contracted the disease, Dr Kent Brantly, 33, and Nancy Writebol, 59, were released from hospital in Atlanta this week after three weeks of being cared for in the US hospital. The pair were treated with an untested serum, ZMapp, which had been trialled on monkeys but not approved for human use.
Since the "miraculous" recovery of the American medics, a small quantity of ZMapp has been sent to Liberia for use on patients there. There are only limited quantities of the drug, as it has not yet been approved for mass production.
The virus, which first emerged in the 1960s, has killed almost 1,500 people across West Africa in the worst-ever outbreak of the disease. The majority of cases have been registered in Sierra Leone, Liberia and Guinea – where this outbreak began on April 1.
But it has also spread to Nigeria – Africa's most populous country – and has infected people beyond the original victim and his carers.
Patrick Sawyer died in Lagos after travelling from Liberia, and was due to travel home to the United States.
In all, 213 people are now under surveillance in Nigeria - including six people, all "secondary contacts" like the caregivers' spouses, being monitored in the state of Enugu, more than 310 miles east of Lagos.
Sierra Leone has been hit hard by the current outbreak, recording at least 910 cases and 392 deaths, according to figures released on Friday by the World Health Organization.
A total of 2,615 infections and 1,427 deaths have been recorded across West Africa.
The spread of the infection has been worsened by the fact that many in Sierra Leone fear Western medicine, and have taken their relatives away from care centres. As a result they die in the community unrecorded, leading to "shadow zones".
On Friday the Ivory Coast closed its borders with Liberia and Guinea. A day later the Philippines announced that they were withdrawing their UN peacekeeping troops from Liberia in response to the outbreak.
The World Health Organisation declared the outbreak an "international public health emergency" on August 8.
"Declaring Ebola an international public health emergency shows how seriously WHO is taking the current outbreak; but statements won’t save lives," said Dr Bart Janssens, MSF Director of Operations.
"Now we need this statement to translate into immediate action on the ground. For weeks, MSF has been repeating that a massive medical, epidemiological and public health response is desperately needed to saves lives and reverse the course of the epidemic. Lives are being lost because the response is too slow.”
Dr Janssens said that there needed to be an urgent scaling-up of medical care, training of health staff, infection control, contact tracing, epidemiological surveillance, alert and referral systems, community mobilisation and education.
He added: "MSF currently has 66 international and 610 national staff responding to the crisis in the three affected countries. All our Ebola experts are mobilised, we simply cannot do more."
