Monkeypox could be a viral virus, experts say, which could be behind the outbreak in the UK.
It was previously thought that the virus could only spread through close contact, including ulcers or through respiratory droplets from an infected person.
But new evidence suggests that the virus can also be transmitted sexually, a link that has never been seen before.
Four out of seven cases seen in the UK in the past two weeks have been homosexual or bisexual, which “strongly indicates” that sex is a source of infection, experts say.
Mateo Prochazka, a sexually transmitted disease specialist and head of the British Health Security Agency’s team investigating monkey cases, said sex had never been described as a means of transmission.
He wrote on Twitter: ‘Close contact between two people (such as during sex) can facilitate transmission – but this has never been explained before.
“However, the vast majority of cases in the current outbreak in the UK which are gay or bisexual (4/7, 57%) strongly suggest prevailing in sex networks.
“This is further enhanced by the fact that normal communication has only been identified in two of the last four cases.”
He added that this would mean that the virus could be transmitted sexually, but that was not his main method, like shigella.
“What’s even more shocking is finding cases that appear to be sexually transmitted – this is a new form of transmission that will have an impact on the response and control of HIV. The epidemic,” Mr Prochazka said.
He added that sexual health services will be instrumental in ending this scourge, and that it will also be important to “address debates that perpetuate inequality and stigma”.
Scientists are divided on the theory, with some agreeing that it may be the first document of a viral infection during sex.