Since monkeypox began sickening thousands of people around the world this spring, two big questions have arisen: Why is a virus that never managed to spread beyond a few cases outside of Africa suddenly causing such a global outbreak? great? And why the vast majority of those affected are men who have sex with men (MSM)?
A long history of work on sexually transmitted infections (STIs) and early studies of the current outbreak suggest the answers may be related: the virus may have made its way into highly interconnected sexual networks within the MSM community, where it can spread in ways it cannot in the general population.
An epidemiological modeling study published as a preprint last week by researchers at the London School of Hygiene & Tropical Medicine (LSHTM) supports that idea. It suggests that the outbreak will continue to grow rapidly if the spread is not reduced. It also has implications for how to protect those most at risk and limit the spread, while suggesting that the risk to the general population remains low.
But there are still many uncertainties, and communication is strained because of the risk of stigmatizing MSM, and because it is difficult to communicate openly about sexual behavior. “I think we need to talk more about sex,” says Gregg Gonsalves, an epidemiologist at the Yale School of Public Health and a former HIV activist. “Everyone has been very clear about the stigma and has said it over and over again. The point is that you still need to address the risk of infection in our community.”
Since early May, more than 2,000 cases of monkeypox have been reported in more than 30 countries where the virus is not normally seen. (Outbreaks are most common in at least a dozen countries in West and Central Africa, where the virus has animal reservoirs. More than 60 cases and one death have been confirmed this year.)
The vast majority of cases in the current outbreak have been in MSM. Researchers at the UK Health Security Agency (UKHSA), for example, asked patients to fill out questionnaires. Of 152 who did, 151 said they were MSM, the team wrote in a technical report published June 10; the remaining patient refused to answer. Other countries have seen similar patterns.
That could be a biased image, of course. “MSM have a better relationship with doctors than straight men,” says Lilith Whittles, an infectious disease modeler at Imperial College London, which could mean they are more likely to report monkeypox symptoms and get tested for the virus. virus. “I don’t know if we’re necessarily looking at heterosexual social media enough to conclude that this isn’t a broader problem,” says Boghuma Titanji, an Emory University virologist who works in a sexual health clinic.
But most researchers say that “determination bias” is unlikely to explain the surprising pattern. Although some monkeypox patients have mild infections that may be missed or misdiagnosed, others have very characteristic rashes and agonizing pain that require hospitalization for pain management. If many people outside of the MSM community had monkeypox, more would have shown up in the statistics by now.
Ashleigh Tuite, an infectious disease epidemiologist at the University of Toronto, says she “understands the hesitancy” to focus on MSM, given the risk of stigma that could worsen discrimination and cause those affected to delay seeking care. “But based on the data that we have and the contact tracing that has been done, it is very clear that this is an MSM-centric outbreak right now,” she says. “Anyone can get monkeypox, but we’re seeing disease activity primarily among” MSM, confirms Demetre Daskalakis, an HIV prevention specialist at the US Centers for Disease Control and Prevention.
Sexual encounters clearly play a role in transmission. Of the 152 people in the UKHSA dataset, 82 were invited for additional interviews focused on their sexual health. Among the 45 who participated, 44% reported having more than 10 sexual partners in the previous 3 months and 44% reported having group sex during the incubation period. Exactly how the virus is transmitted is less clear. Researchers have found viral DNA, and even infectious virus, in the semen of some patients, but they are not sure that it is important for transmission; skin-to-skin contact may be sufficient. (Other STIs, including herpes and scabies, are also primarily spread this way.)
Graeme Lamb, who works at a Toronto bathhouse for men who have sex with men, recently helped organize a monkeypox vaccination clinic there for people at high risk of infection.STEVE RUSSELL/STAR OF TORONTO VIA GETTY IMAGES
For those who study how pathogens spread through social and sexual networks, the pattern is not much of a surprise. In the 1970s and 1980s, researchers trying to understand the spread of sexually transmitted diseases like gonorrhea were stumped, says LSHTM epidemiologist Adam Kucharski: Survey data showed that the average number of sexual partners people it was too low to maintain transmission. But the averages obscure that while many people have few sexual partners, some have a large number. This helps drive transmission because if they are infected, they are also more likely to infect others.
Sexual networks among MSM are no different in nature from those of other groups, Whittles emphasizes, but a core group of people is much more connected than people outside the MSM community. They change partners more often and are more likely to have multiple partners at the same time. “These things happen in all sexual networks, it’s just a matter of degree,” says Whittles. And in a densely connected network, the virus is less likely to hit a dead end.
“It’s very possible that this epidemic is spreading among a subset of people just because that subset is networked differently from everyone else,” says Keletso Makofane, a social media epidemiologist at the FXB Center for Health and Rights. Humans at Harvard University. Along with his colleagues, Makofane hopes to launch a study in New York City in August to better understand the spread of the disease. “The idea is to get an idea of how many people report symptoms that are consistent with monkeypox and how they are connected,” he says.
The LSHTM study, published on medRxiv June 13, used UK data on patterns of intercourse to model the spread of monkeypox among MSM and beyond. Because it is not yet clear how contagious the virus is, the researchers modeled scenarios based on different levels of risk. Without effective intervention measures or behavioral changes, a large and sustained outbreak with more than 10,000 cases among MSM worldwide is “highly likely,” they write. “In contrast, sustained transmission in the non-MSM population is unlikely in all scenarios considered.”
Because the model is based on UK data, the findings may not apply elsewhere, says first author Akira Endo. And other factors may have made the outbreak worse. Monkeypox may have mutated in a way that allows it to be transmitted more easily, and the proportion of the population that has received the smallpox vaccine, which also offers some protection against monkeypox, is declining because smallpox vaccination was abandoned around the world starting in the 1970s. But the model shows that “we don’t necessarily need [those factors] to explain the observed patterns,” says Endo.
These findings put epidemiologists in a delicate position, and some refused to speak to Science for fear of stigmatizing MSM. Endo says he understands that and agrees the findings could easily be misunderstood. “In the meantime, I also understand that there is a risk in the other direction: that information doesn’t reach those who need it most before it’s too late,” he says.
Whittles agrees, calling the findings “practical information, in terms of where it’s spreading. It’s a morally neutral thing,” he says. “Knowledge of what is happening is power, even if that knowledge is imperfect and changes,” adds Daskalakis.
The virus could still find other networks with similar characteristics. Daskalakis recalls an outbreak of methicillin-resistant Staphylococcus aureus in the US in the 2000s that began in the MSM community but then spread to gyms, among athletes, and in prisons. Monkeypox could also start to spread among sex workers and their clients, says Tuite.
How quickly the virus will spread in the coming months depends on control efforts. National health authorities in Europe, Canada and the United States have issued guidelines on how to reduce the risk of infection, and dating apps have alerted users to the risk of monkeypox and its symptoms, which can change contact patterns. Increased awareness among healthcare workers may also have an impact, Whittles says: faster diagnoses mean patients will isolate earlier in their infection, reducing further transmission. “So there are a couple of different ways that behavior can change, even if it’s not about people having less sex,” she says. And the model did not take into account that infected people developed immunity. That means “we may see a slowdown in the outbreak sooner than we imagined,” says Endo.
Many countries are also preparing to launch immunization campaigns. Targeting those with many sexual partners may be the most efficient approach. In new guidance published June 21, the UKHSA announced it would begin offering vaccinations to MSM at higher risk: “Risk criteria would include a recent history of multiple partners, engaging in group sex, attending on-site sex venues or a proxy marker such as recent bacterial STI (within the last year)”.
It’s important to alert that community and do it the right way, says Gonsalves. “We should say: It’s not about who you are. It’s about what you’re doing. And we are not going to stigmatize it. But know that you are at greater risk if you fit this profile.”
Correction, June 22, 10:10 am: This story has been changed to note that Lamb is an employee, not a manager, of the Toronto Bathhouse.
Source: www.science.org