Two cases of the rare, infectious illness Lassa fever have been identified in the UK.
The UK Health Security Agency (UKHSA) said another probable case was under investigation. The cases are within the same family in the East of England and are linked to recent travel to West Africa.
One of the cases has recovered, while the other is receiving specialist care at the Royal Free London NHS Foundation Trust.
The probable case is receiving care at Bedfordshire Hospitals NHS Foundation Trust.
Health experts have insisted the overall risk to the public is low.
Lassa fever is an acute viral haemorrhagic illness caused by the Lassa virus.
People usually become infected with Lassa virus through exposure to food or household items contaminated with urine or faeces of infected rats – present in a number of West African countries where the disease is endemic.
The virus can also be spread through infected bodily fluids.
People living areas of west Africa with high populations of rodents are most at risk of Lassa fever and imported cases rarely occur elsewhere in the world., the UKHSA said.
It added cases which occur elsewhere are “almost exclusively in people who work in endemic areas in high-risk occupations such as medical or other aid workers”.
Most people with Lassa fever will make a full recovery, however severe illness can occur in some individuals. One of the cases has recovered, while the other will receive specialist care at the Royal Free London NHS Foundation Trust.
Dr Susan Hopkins, chief medical adviser at the UKHSA, said: “Cases of Lassa fever are rare in the UK and it does not spread easily between people.
“The overall risk to the public is very low.
“We are contacting the individuals who have had close contact with the cases prior to confirmation of their infection, to provide appropriate assessment, support and advice.”
The last two cases in UK occurred in 2009, and there have only ever been eight cases of Lassa fever imported to the UK since 1980.
There was no evidence of onward transmission from any of these cases.