Scientists begin to understand when and how monkeypox spreads

In last summer’s monkeypox outbreak in the United States and dozens of other countries, men who have sex with men were most at risk. But thousands of women were also infected and many more cases likely went unreported, according to the first study of women and non-binary people who contracted the disease.

As with men, sexual contact was the most likely source of infection among transgender women, accounting for 89% of cases, according to the series of cases published last Thursday (17) in the journal Lancet. But among cisgender women and non-binary individuals who were assigned female at birth, only 61% of cases can be connected to sexual contact.

Nearly a quarter of the cisgender women in the study could have been infected without sexual interaction with an infected person, said Chloe Orkin, a physician and researcher at Queen Mary University of London. The women are believed to have been infected through exposure at their jobs or homes, or through other types of close contact.

“The lesson is that everyone needs to know this,” Orkin said. While it’s appropriate that public health messages have been directed primarily at men who have sex with men, she added, “It’s important to recognize that this is not the only group.”

After several months of rapidly increasing cases, the monkeypox outbreak in the United States has subsided, thanks in part to a vaccination campaign and changes in the behavior of many high-risk individuals. Since May, there have been just over 29,000 cases in the United States, but only about 1,000 cases were diagnosed last month.

However, as the disease loses public attention, scientists are just beginning to understand when and how it spreads and who is at risk.

In the new study, Orkin and his colleagues found genetic material from the monkeypox virus in all 14 vaginal swabs they tested, suggesting that the virus can be transmitted through genital secretions. Studies in men have also found the virus in seminal fluid.

Still, public health officials are hesitant to call monkeypox a sexually transmitted infection, arguing that the virus can be spread by close physical contact of any kind.

Some experts disagree, however: The fact that monkeypox can be transmitted in other ways should not preclude its classification as a sexually transmitted disease, because other diseases, such as herpes and syphilis, can also be spread by non-sexual close contact, some say. .

Last month, New York state added monkeypox to its list of sexually transmitted infections, but the Centers for Disease Control and Prevention has not made that change. The agency will leave that categorization to individual states, said Demetre Daskalakis, deputy coordinator of the White House monkeypox response. But it’s clear that sexual behavior drives cases, he said.

“If you took away the sex, would we have a monkeypox outbreak? Probably not,” he added. Even though the main reason for spread is skin-to-skin contact during sexual activity, “it’s definitely sexually associated transmission.”

This year, Orkin led an international collaboration to characterize monkeypox symptoms in 500 patients. The findings have prompted Britain, the United States and other countries to refine their case definitions of the disease.

And last month the UK Health Security Agency published a study suggesting that approximately 40% to 60% of monkeypox transmission may occur before infected people develop symptoms.

That makes intuitive sense because once patients develop painful blisters, they’re unlikely to have sex, said Tom Ward, an infectious disease modeler at the agency. A small percentage of infected people may never develop symptoms, he said.

Contact tracing in a monkeypox outbreak is extremely challenging due to the sensitive and often anonymous nature of the spread; there are no tests capable of detecting the disease before the characteristic rash appears.

“What essentially stands out is that we still need a lot of research into the nature of asymptomatic and pre-symptomatic monkeypox transmission,” said Ward.

Some people may experience mild, generic symptoms, such as a sore throat, before the rash develops.

The new study is the first to describe monkeypox in trans or nonbinary people, who often have little access to quality health care and are rarely included in research studies.

“It’s really, really important that we report sex and gender differences because both are important and in some cases they intersect,” Orkin said.

In the study, researchers from 15 countries contributed clinical information from 69 cisgender women, 62 transgender women and five non-binary individuals who were diagnosed with monkeypox between May 11 and October 4. About 45% of the women were Latino, 29% were white, and 21% were black.

More than half of the patients in the study had sores on the anus, genitals, mouth or eyes. But some women — especially cisgender women — were initially misdiagnosed with other sexually transmitted infections.

Experts predicted that monkeypox “would likely have a slightly different pattern of transmission depending on the social behaviors and norms of certain groups,” said Abraar Karan, an infectious disease physician at Stanford University.

The new study supported this inference. In contrast to male monkeypox patients who have sex with men, only 7% of patients in the study reported having attended a gay pride event or other similar gatherings. While transgender women in the study had an average of ten partners in the past month, cisgender women had one, and 7% of cisgender women said they had no sexual partners in the past month.