A British national living in Sierra Leone has tested positive for the deadly virus Ebola, the Department of Health said.
It is the first reported case of a Briton contracting the virus.
The overall risk to those in the UK "continues to be very low", said the Department of Health.
Professor John Watson, deputy chief medical officer, said: "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 overall risk to the public in the UK continues to be very low."
Some 1,427 people have died since an outbreak in West Africa, which the World Health Organisation (WHO) said is growing at an "unprecedented" rate.
Journalist Katie Mark told Sky News that people in Sierra Leone were often too scared to tell medical authorities that they were infected.
"There are not enough resources being put into stopping the spread of Ebola. If someone dies the body can be sitting there for up to eight days and in that time the disease can spread further.
"There is not enough knowledge about the virus and people are scared to report it.
"They see Ebola as a death sentence, that if the family is going to die they would rather they die at home. They do not realise that if they get treatment their chance of survival is greatly increased."