Since smallpox began infecting thousands of people around the world this spring, two big questions have arisen: Why did the virus, which had not spread outside Africa for so long, suddenly lead to such a large, global epidemic? Why is the vast majority of affected men (MSM) having sex with men?
A long history of cases of sexually transmitted infections and preliminary studies of the current epidemic suggest answers: The virus may have penetrated closely related sexual networks in the MSM community, where it cannot spread to the general population. .
Researchers at the London School of Hygiene and Tropical Medicine (LSHTM) supported the idea in an epidemiological modeling study published last week as a preliminary publication. If the spread is not reduced, the epidemic is expected to grow rapidly. It also affects how to protect and limit the spread of endangered species, while the risk remains low for the general population.
However, there is still a lot of uncertainty and communication is difficult because of the risk of MSM stigmatization and the difficulty of speaking openly about sexual behavior. “I think we need to talk more about sex,” said Gregg Gonsalves, an epidemiologist and former HIV activist at the Yale School of Public Health. “Everyone spoke openly about the stigma and repeated it over and over again. By the way, you still have to deal with the risk of infection in our society. ”
Since the beginning of May, more than 2,000 cases of smallpox have been reported in more than 30 countries where the virus has not been detected. (The virus is endemic in at least a dozen countries in West and Central Africa with animal reservoirs. More than 60 cases and one death have been confirmed this year.)
The vast majority of cases in the current epidemic have been in MSM. Researchers from the UK Health Agency (UKHSA), for example, asked patients to fill out a questionnaire. Of the 152 perpetrators, 151 said they were MSM, the team wrote in a June 10 technical briefing; The remaining patient refused to respond. Other countries have seen similar examples.
This can, of course, be a distorted image. “MSM has a better relationship with doctors than heterosexual men,” said Lilith Whittles, an infectious disease model at Imperial College London, who said their monkeys could be tested for the virus by reporting smallpox symptoms. Boguma Titanji, a virologist at Emory University’s Sexual Health Clinic, said: “I don’t know if we’re looking for enough to conclude that heterosexual social media is not a widespread problem.”
However, according to most researchers, such “one-sidedness of definition” does not explain the surprising pattern. Although some cases of smallpox in monkeys go undiagnosed or have mild infections that can be diagnosed, very common rashes and illnesses require hospitalization for treatment. If many people outside the MSM community had contracted monkey disease, many more people would now be ignored in the statistics.
Ashley Twitte, an epidemiologist at the University of Toronto, says she “understands” the focus on MSM, given the risk of stigma that could exacerbate discrimination and delay victim care. “But based on the information we have and the search for contacts, it’s clear that this is an MSM-targeted epidemic,” he said. “Anyone can be infected with smallpox, but we see the activity of the disease primarily among MSM,” said Demetre Daskalakis, an HIV prevention specialist at the US Centers for Disease Control and Prevention.
Clearly, sexual intercourse plays a role. Of the 152 people on the UKHSA database, 82 were invited for an additional sexual health interview. Of the 45 participants, 44% reported having more than 10 sexual partners in the previous 3 months and 44% had group sex during the incubation period. It is unknown how the virus was transmitted. Researchers have found viral DNA or even an infectious virus in the seeds of some patients, but do not know that they are important for transmission; Touching the skin may be enough. (Other sexually transmitted infections, including herpes and scabies, are also primarily transmitted in this way.)
This is not a big surprise for those who study how pathogens spread through social and sexual networks. Researchers who tried to understand the prevalence of sexually transmitted diseases, such as gonorrhea, in the 1970s and 1980s, were surprised, says Adam Kucharski, an epidemiologist at LSHTM: Surveys show that the average number of sexual partners in humans is too small to carry the disease. However, the average person does not realize that many people have fewer sexual partners, but some have more. This helps to spread the disease, because if they are infected, they can spread it to others.
Whittles noted that sexual networks between MSMs are no different in nature from other groups, but that the majority of people are more closely connected than people outside the MSM community. They change partners frequently and have more than one partner at a time. “These things happen in all sexual networks, it’s just a level issue,” Whittles said. In a dense network, however, the virus is less likely to get stuck.
Keletso Makofane, a social network epidemiologist at Harvard University’s FXB Center for Health and Human Rights, said: “This epidemic is likely to be exacerbated in some people because they are connected to the network differently than others.” Together with colleagues, Macofane hopes to begin a study in New York in August to better understand the spread of the disease. “The idea is to understand how many people have reported symptoms that correspond to monkey smallpox and how they are related,” he says.
The LSHTM study, published on medRxiv on June 13, used UK data on sexual partnership patterns to model the prevalence of smallpox in MSM and beyond that group. Since the extent of the virus is still unknown, researchers have modeled scenarios based on different levels of risk. Without effective intervention or change in behavior, they write, a large and persistent epidemic with more than 10,000 cases among MSMs around the world is “highly likely”. “In contrast, MSM is unlikely in all scenarios involving sustained infection in a non-population.”
Because the model is based on UK data, the findings may not be used elsewhere, says first author Akira Endo. And other factors could exacerbate the epidemic. Smallpox may have been mutated for its easy transmission, and the proportion of people who have been vaccinated against smallpox is declining because smallpox vaccination has been discontinued worldwide since the 1970s. But modeling “we don’t necessarily need [those factors] to explain the observed patterns, ”says Endo.
Such findings have left epidemiologists vulnerable, with some refusing to talk science Fear of slandering MSM. Endo says he understands this and may not easily understand the conclusions. “At the same time, I understand that there is a danger in other areas as well – the information will not reach the most needy before it’s too late,” he said.
Whittles agreed, calling the findings “practical information on where they are spreading.” It’s morally neutral, ”he said. “Knowing what is happening is a force, but that knowledge is not perfect and will change,” adds Daskalakis.
The virus can still find other networks with similar characteristics. Daskalakis recalls the emergence of methicillin-resistant disease in the United States Staphylococcus aureus It began in the MSM community in the 2000s and later spread to gyms, athletes and prisons. Smallpox can also spread to sex workers and their clients, Twitte said.
How quickly the virus spreads in the coming months will depend 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 warned users about the dangers of monkey disease and its symptoms, which could change communication patterns. Raising awareness among health care providers could also have an impact, Whittles said. “So behavior can change several times, even if there aren’t people who have less sex,” she says. The model did not take into account people with immune-boosting infections. This is “we may see a slowdown in the epidemic sooner than we think,” Endo says.
Many countries are preparing to launch vaccination campaigns. Vaccination of people with multiple sexual partners may be the most effective method; In the Canadian province of Quebec, the vaccine has been offered to MSM, which has had two or more sexual partners in the past 14 days. It’s important to warn the public and do it the right way, Gonsalves said. “We have to say, it’s not about who you are. It’s about what you’re doing. And we do not slander it. But know that if you fit this profile, you take more risks. “