A total of two people have so far been confirmed to have the 'Ebola-like' lassa fever virus in the UK, according to the UK Health Security Agency (UKHSA).
The rat-born virus is potentially lethal and is causing concern after being identified in the country for the first time in over a decade.
A third patient is currently being checked.
Lassa fever is similar to Ebola and is an epidemic in a number of African countries.
Those infected are based in the East of England and recently returned from visiting family in Western Africa.
There have been no cases identified in Scotland so far.
The disease spreads through food contaminated with the faeces and urine of infected rats and via human bodily fluid.
Symptoms
Symptoms include headaches, a sore throat, aches and pains, vomiting and diarrhoea.
The virus can also trigger bleeding from the mouth and nose and vaginal bleeding in women.
Symptoms may then progress if the illness is not promptly treated, causing shock, seizures, comas and temporary deafness.
However, about 80 per cent of those infected show no symptoms at all.
Is lassa fever deadly?
Roughly one per cent of people infected with the Lassa virus die, according to the World Health Organisation (WHO).
Dr Susan Hopkins, chief medical advisor at UKHSA, said: “We can confirm that two cases of Lassa fever have been identified in England, and a further probable case is under investigation.
"The cases are within the same family and are linked to recent travel to West Africa.
“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 UKHSA and the NHS have well established and robust infection control procedures for dealing with cases of imported infectious disease and these will be reinforced."
Where are the confirmed cases?
One of the UK cases has been taken to the Royal Free London NHS Foundation Trust hospital for specialist treatment.
The other confirmed case has since recovered, with a third currently at Bedfordshire Hospitals NHS Foundation Trust receiving medical attention.
The cases are the ninth and tenth confirmed in the UK since 1980, and the first in 13 years.
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