The recent outbreak of monkeypox virus infections is being linked to events taking place in Spain and Belgium, according to a leading advisor to the World Health Organisation (WHO).

Dr David Heymann, who formerly headed the WHO’s emergencies department, told the Associated Press (AP) the primary theory to explain the spread of the disease was sexual transmission at raves taking place in the two countries.

The WHO has recorded more than 90 cases of monkeypox in a dozen countries. Dr Heyman has described the unprecedented outbreak in developed countries as “a random event”.

Where monkeypox has been detected

Cases have been confirmed in Canada, Spain, Israel, France, Switzerland, the US and Australia.

On Monday, Denmark announced its first case, Portugal revised its total up to 37, Italy reported one further infection and Britain added 37 more cases taking its current total to 56.

Germany has four confirmed cases linked to exposure at “party events… where sexual activity took place” in Spain’s Canary Islands and in Berlin, according to a government report obtained by the AP.

Madrid’s senior health official said on Monday that the Spanish capital had 30 confirmed cases. Enrique Ruiz Escudero said authorities are investigating possible links between a recent Gay Pride event in the Canary Islands, which drew 80,000 people, and cases at a Madrid sauna.

Monkeypox had not previously triggered widespread outbreaks beyond Africa, where it is endemic in animals.

How is monkeypox being spread?

Chelmsford Weekly News: The monkeypox virus can be spread in a number of ways. Picture: PAThe monkeypox virus can be spread in a number of ways. Picture: PA

There are a number of ways monkeypox can be spread, including close contact with an infected person.

“We know monkeypox can spread when there is close contact with the lesions of someone who is infected, and it looks like sexual contact has now amplified that transmission,” said Dr Heymann.

That marks a significant departure from the disease’s typical pattern of spread in central and western Africa, where people are mainly infected by animals like wild rodents and primates and outbreaks have not spilled across borders.

Health officials say most of the known cases in Europe have been among men who have sex with men, but anyone can be infected through close contact with a sick person, their clothing or bedsheets. Scientists say it will be difficult to establish whether the spread is being driven by sex or merely close contact.

“By nature, sexual activity involves intimate contact, which one would expect to increase the likelihood of transmission, whatever a person’s sexual orientation and irrespective of the mode of transmission,” said Mike Skinner, a virologist at Imperial College London.

Authorities in Britain, Spain and Portugal have said most of the cases identified so far were in young men whose infections were picked up when they sought help for lesions at sexual health clinics.

Dr Heymann, who is also a professor of infectious diseases at the London School of Hygiene and Tropical Medicine, said the monkeypox outbreak was likely to be a random event that might be traceable to a single infection.

“It’s very possible there was somebody who got infected, developed lesions on the genitals, hands or somewhere else, and then spread it to others when there was sexual or close physical contact,” he said. “And then there were these international events that seeded the outbreak around the world, into the US and other European countries.”

At a public session on Monday, WHO officials described the outbreak as “containable” and cautioned against stigmatising affected groups, saying the disease can infect anyone.