Monkeypox: 95% spread occurred via sexual activity, says study

Sexual closeness is the most likely route of transmission in 95 per cent of monkeypox cases, according to a global case study series from across 16 countries. However, the virus can be transmitted by any close physical contact through large respiratory droplets and potentially through clothing and other surfaces, said researchers at Queen Mary University of London.

In the study, the team reported 528 infections diagnosed between April 27 and June 24, 2022, at 43 sites in 16 countries. The findings, published in the New England Journal of Medicine (NEJM), showed 95 per cent of the persons presented with a rash (with 64 per cent having less than 10 lesions), 73 per cent had anogenital lesions, and 41 per cent had mucosal lesions (with 54 having a single genital lesion).

Overall, 98 per cent of the persons with infection were gay or bisexual men, 75 per cent were white, and 41 per cent had human immunodeficiency virus infection.

Common systemic features preceding the rash included fever (62 per cent), lethargy (41 per cent), myalgia (31 per cent), and headache (27 per cent); lymphadenopathy -- swelling of lymph nodes -- was also common (reported in 56 per cent). Concomitant sexually transmitted infections were reported in 109 of 377 persons (29 per cent) who were tested.

Among the 23 persons with a clear exposure history, the median incubation period was 7 days. Monkeypox virus DNA was detected in 29 of the 32 persons in whom seminal fluid was analysed.

In addition, the study also identified new clinical presentations in people with monkeypox, not recognised in current medical definitions of monkeypox.

These symptoms include single genital lesions and sores on the mouth or anus. The clinical symptoms are similar to those of sexually transmitted infections (STIs) such as syphilis or herpes and can easily lead to misdiagnosis.

In some people, anal and oral symptoms have led to people being admitted to hospital for management of pain and difficulties swallowing. It's important that these new clinical symptoms be recognised and healthcare professionals be educated on how to identify and manage the disease - misdiagnosis can slow detection and thus hinder efforts to control the spread of the virus, the team said.

"We have shown that the 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," said Chloe Orkin, Professor of HIV Medicine at QMUL.

"We have also found monkeypox virus in a large proportion of the semen samples tested from people with monkeypox. However, this may be incidental as we do not know that it is present at a high enough levels to facilitate sexual transmission. More work is needed to understand this better," added Dr John Thornhill, Consultant Physician in Sexual Health.

These findings will improve future diagnosis, help to slow the spread of infection and help the international community prioritise the limited global supply of monkeypox vaccines and treatments to communities most at risk, the researchers said.