After the UK Health Security Agency (UKHSA) detected four cases of monkeypox in gay, bisexual men, the health officials are investigating whether the virus may spread during sexual contact, the media reported.
The rare tropical disease, endemic in Africa, was known to spread via close contact - but it had never been linked to sexual intercourse, the Guardian reported.
According to the UKHSA, the four new cases - three in London and one linked case in the northeast of England - do not have known connections with the previous confirmed cases, although two are known to each other, signalling that the virus could be spreading in the community for the first time. The first case had a travel history to Nigeria.
Four of the cases are in gay or bisexual men, prompting health officials to ask them to be extra vigilant for new lesions or rashes.
The experts at the UKHSA also claimed the pattern of spread is "highly suggestive of spread in sexual networks", the report said.
It was "bizarre that cases appear to have acquired the infection via sexual contact", said Mateo Prochazka, an STI expert and head of the UKHSA team probing the outbreak, in a Twitter thread.
"This is a novel route of transmission that will have implications for outbreak response and control.
"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 said.
However, other experts disagreed and said while the new cases are a novelty, it has not been established that sex is the virus' primary route of transmission, nor does it make it an STI.
"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 public health expert from the University of Southampton, was quoted as saying.
"Although the current cluster of cases is in men who have sex with men, it is probably too early to make conclusions about the mode of transmission or assume that sexual activity was necessary for transmission, unless we have clear epidemiological data and analysis," added Dr Michael Skinner, a virologist at Imperial College of London.
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