A healthcare worker from the Blackpool Victoria Hospital is being treated in Newcastle after coming into contact with one of the earlier victims before the virus had been diagnosed.
The previous cases had each independently travelled to Nigeria where there has been an outbreak of the disease.
Public Health England said it is taking a "highly precautionary approach" and is monitoring closely anyone who has been in contact with an infected person, as infection can be serious in rare cases.
The Independent
More about: monkeypox
