A total of 120 confirmed or suspected cases have been reported globally, including 20 in the UK with the majority of infections in Spain linked to a sauna in Madrid. The World Health Organisation said there were a further 28 suspected cases, in addition to the 92 confirmed in 12 member states which were not endemic for the virus.
The global figure is unprecedented for a disease that is normally confined to central and west Africa.
Monkeypox does not spread easily between people, so doctors have been puzzled by the outbreak and by the appearance of cases on different continents at the same time.
The virus is only transmitted from person to person through close physical contact – including sexual intercourse.
David Heymann, an infectious disease specialist at the World Health Organisation, said he believed the pox had entered the population as a “sexual form”.
He said: “What seems to be happening now is that it has got into the population as a sexual form, as a genital form, and is being spread as are sexually transmitted infections, which has amplified its transmission around the world.”
The president of the British Association for Sexual Health and HIV (BASHH) told Sky News that some clinic staff have received the smallpox vaccine, which can be effective against monkeypox, and talks are taking place about giving doses to “potential risk groups”.
Dr Claire Dewsnap said: “Our response is really critical here.
“There is going to be more diagnoses over the next week. How many is hard to say.
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Dr Dewsnap said she was concerned about the impact on other infections as staff are diverted to deal with monkeypox, when the “public health budget has decreased significantly over the last 10 years”.
She said: “Some clinics that have had cases have had to advise people not to walk in.
“They’ve primarily done that because if somebody has symptoms consistent with monkeypox, we don’t want people sat in waiting rooms potentially infecting other people.
“They’ve implemented telephone triage to all of those places.”
The UK Health Security Agency has said a notable proportion of recent cases in Britain and Europe have been found in gay and bisexual men.