Largest study to date reveals some sufferers have been admitted to hospital with painful genital lesions or difficulty swallowing
The symptoms, which include genital lesions and sores on the mouth or anus, may be severe and have led some sufferers to be admitted to hospital for pain management and difficulties swallowing, researchers say.
But the lesions or sores can easily be misdiagnosed, the scientists warn.
Since monkeypox began rapidly spreading across the globe in May, there are now more than 15,000 cases worldwide, leading the World Health Organisation to reconsider whether to declare it a global crisis.
Research has found it is mutating up to 12 times faster than expected.
Gay and bisexual men account for 98 per cent of infections. Although sexual closeness is the most likely route of transmission, the virus may also be transmitted by close contact through large droplets breathed in and potentially through clothing and other surfaces.
The usual reported symptoms include fever, headache, muscle aches, swollen lymph nodes, exhaustion and pimples or blisters on the face, in the mouth, and on other parts of the body.
But now the largest analysis to date, based on examining more than 500 cases and published in the in The New England Journal of Medicine (NEJM), has found many people infected were suffering symptoms not listed in medical definitions of monkeypox.
The experts at Queen Mary University of London and others from 16 countries involved in the research say their work will aid diagnosis and help to slow the global spread through public-health intervention aimed at the high-risk group.
They say once someone is diagnosed, contact-tracing and advising them to isolate will be key to limiting disease spread because there is a global shortage of vaccines, and misdiagnosis hinders work to control its spread.
Earlier this month, separate research published in the Lancet Infectious Diseases Journal also showed monkeypox can mimic other common STIs such as herpes and syphilis. The study also found a quarter of patients had another STI.
Chloe Orkin, professor of HIV medicine at Queen Mary University of London, said: “Current international case definitions need to be expanded to add symptoms that are not currently included, such as sores in the mouth, on the anal mucosa and single ulcers.
“These particular symptoms can be severe and have led to hospital admissions so it is important to make a diagnosis.”
John Thornhill, consultant physician in sexual health and HIV at Barts NHS Health Trust, said: “While we expected various skin problems and rashes, we also found that one in 10 people had only a single skin lesion in the genital area, and 15 percent had anal and/or rectal pain.
“These different presentations highlight that monkeypox infections could be missed or easily confused with common sexually transmitted infections such as syphilis or herpes.”
He said they also found monkeypox virus in a large proportion of semen samples from people infected.
“However, this may be incidental as we do not know that it is present at high enough levels to facilitate sexual transmission. More work is needed to understand this better.”
Claire Dewsnapp, of the British Association for Sexual Health, called for measures to co-ordinate the UK response to monkeypox, as well as more funding to contain and eliminate it, including acquiring vaccines and a national plan for testing, treatment and prevention.