Monkeypox is likely to be a sexually transmissible virus, experts believe, that may be driving the outbreak in Britain.
Previously it was believed the virus could only spread by close contact including with lesions or via an infected person’s exhaled respiratory droplets.
But emerging evidence indicates the virus could also be contracted during sexual intercourse, a link which has never been seen before.
Four of the seven cases seen in England in the past two weeks are in gay or bisexual men and this is “highly suggestive” of sex being a driver of transmission, according to experts.
Mateo Prochazka, an STI expert and the head of the UK Health Security Agency team investigating the monkeypox cases, said sex has never been described before as a means of its transmission.
He tweeted: “Close contact between two people (such as during sex) could facilitate transmission – but this has never been described before.
“However, the high proportion of cases in the current outbreak in England that are gay or bisexual (4/7, 57 per cent) is highly suggestive of spread in sexual networks.
“This is further suggested by the fact that common contacts have been identified for only two of the four latest cases.”
He added that this would mean the virus could be transmitted through sex, but it was not its primary route, much like shigella.
“What is even more bizarre is finding cases that appear to have acquired the infection via sexual contact - this is a novel route of transmission that will have implications for outbreak response and control,” Mr Prochazka said.
He added that sexual health services will be key in squashing the outbreak, and it will also be necessary to “tackle discourses that reinforce inequalities and stigma”.
Scientists are divided on the theory, with some agreeing that this could be the first documentation of the virus being passed during sex.
“This may indeed be the first time transmission of monkeypox via sexual contact has been documented, although it has not been confirmed to be the case,” said Dr Michael Head, a global health scientist from the University of Southampton.
Prof Neil Mabbott, personal chair in immunopathology at the University of Edinburgh, added: “Transmission of monkeypox virus infection in humans by sexual contact has not previously been documented, and the recent cases suggest a potentially novel means of spread.”
Health officials are now urging the gay and bisexual man community to be particularly aware of “any unusual rashes or lesions on any part of their body, especially their genitalia, and to contact a sexual health service if they have concerns”.
Symptoms include fever, headache, muscle aches, backache, swollen lymph nodes, chills and exhaustion.
It also produces a distinctive rash, which often starts on the face before spreading across the body, including the genitals, which the World Health Organisation says can be itchy and painful.
There is no cure for monkeypox and the mortality rate is thought to be around 10 per cent, with most people developing symptoms two weeks after infection and taking two to four weeks to recover.
“There is a need to engage with the at-risk community of gay and bisexual men to ensure they know about the presence of this infection and report any sign and symptoms to health facilities,” said Prof Jimmy Whitworth, professor of international public health at the London School of Hygiene & Tropical Medicine.
However, some scientists have voiced concern over this theory and said a link cannot be assumed.
Prof Francois Balloux, an infectious disease expert and director of the UCL Genetics Institute, said: “I would urge some caution at this stage before concluding that monkeypox may have recently morphed into an STD.
“Monkeypox is not particularly transmissible and the number of cases to date where the route of transmission is known remains relatively small.
“Most ‘sexual contact’ qualifies as ‘close contact’. Thus, the recent observation of apparent transmission through sexual contact in the UK does not necessarily, in itself, imply any recent change in the monkeypox virus routes of transmission.”