Monkeypox has been detected in Portugal and Spain in what could be the first global outbreak of the rare disease, media reports said on Wednesday.
Spain is monitoring eight men who it believes are infected, with tests being carried out to confirm the virus, Daily Mail reported.
All of the men are gay or bisexual, according to local media, and most were detected at STI clinics in Madrid, it said.
Five men in Portugal have also tested positive and at least 15 more cases are being investigated, health officials there said.
These cases are all male and mostly 'young', but it is not yet clear how they caught the virus.
Until now, monkeypox cases were confined to travellers and their relatives returning from western and central Africa, where the virus is endemic.
But experts now fear it is spreading more widely for the first time, after seven Britons were diagnosed in the past fortnight, Daily Mail reported.
Six of them appear to have been infected in the UK and the majority are not linked, which suggests more cases are going undetected.
Four of the British patients are gay or bisexual men, and officials say the pattern of transmission is 'highly suggestive of spread in sexual networks'.
Dr Simon Clarke, a microbiologist at the University of Reading, told MailOnline he suspects UK case numbers are already 'in the tens'.
But he insisted the disease will not spread like Covid, adding: "I would be surprised if we ever got to more than 100 cases (in Britain)."