A patient has been diagnosed with the rare viral infection monkeypox in the south west of England.
It is believed the patient contracted the infection while visiting Nigeria, Public Health England (PHE) said.
According to the World Health Organisation, the condition is similar to human smallpox and although it is much milder, it can be fatal.
The patient has been transferred to a specialist infectious disease centre at Guy's and St Thomas' in London.
PHE and NHS officials said they had been implementing "rapid infection control procedures" and contacting passengers who travelled in close proximity to the patient on the same flight to the UK.
"We are following up with those who have had close contact with the patient to offer advice and to monitor them as necessary," said Dr Meera Chand, consultant microbiologist at PHE.
PHE says the infection is usually a self-limiting illness and most people recover within a few weeks, however severe illness can occur in some individuals.
The infection does not spread easily between people and the risk to the general public in England is very low.