The World Health Organization said on Sunday that the sudden appearance of monkeypox at once in several countries where the disease is not typically found suggests undetected transmission for some time and recent amplifying events.
As of May 26, a total of 257 confirmed cases and 120 suspected cases have been reported from 23 member states that are not endemic for the virus, WHO said in a statement.
Monkeypox is an infectious disease that is usually mild, and is endemic in parts of west and central Africa. It is spread by close contact, so it can be relatively easily contained through measures such as self-isolation and hygiene.
Most of the cases reported so far have been detected in the UK, Spain and Portugal.
"The vast majority of reported cases so far have no established travel links to an endemic area and have presented through primary care or sexual health services," the UN agency said.