How is monkeypox spread? what scientists know

Color transmission electron micrograph (TEM) of monkeypox virus particles (red) found within an infected cell (blue).

Monkeypox virus particles (red) infect a cell (blue), as shown in this color image from a transmission electron microscope.Credit: NIAID/NIH/SPL

As global cases of monkeypox continue to rise, researchers are learning more about how the disease spreads. Early predictions that the virus is transmitted primarily through repeated skin-to-skin contact between people have been largely confirmed, according to a series of new studies.

“When all these studies are put together, we see that the clinical presentation everywhere is similar, but also surprising,” says Oriol Mitjà, an infectious disease researcher at the Germans Trias i Pujol University Hospital in Barcelona, ​​Spain, who co-authored one. of recent studies on the lancet1. That’s because the symptoms and pattern of spread don’t resemble what the researchers observed in West and Central Africa, where the monkeypox virus has caused isolated and persistent outbreaks for decades.

Since early May, monkeypox has spread to more than 90 countries and caused more than 32,000 infections, with nearly a third of reported cases in the United States. The rapid spread of the virus prompted the World Health Organization to issue its highest-level public health alert on July 23; United States President Joe Biden did the same on August 4 by declaring a public health emergency in the United States.

Although some women and children have been infected since May, most cases so far have occurred in men who have sex with men (MSM), especially those with multiple sexual partners or who have anonymous sex. The virus likely took advantage of the dense sexual networks in the MSM community to spread efficiently, says Mitjà. The more the virus continues to spread, the more opportunities it has to infect other populations, including wild animals, which scientists have warned could establish viral reservoirs that could infect humans repeatedly.

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‘Full of viruses’

When a person contracts monkeypox, they may develop flu-like symptoms, enlarged lymph nodes, and distinctive fluid-filled lesions on the skin. Although some researchers have suggested that the monkeypox virus could be spread through respiratory droplets or airborne particles, as SARS-CoV-2 does, Mitjà and colleagues report that samples of skin lesions, collected in the time of diagnosis, contain much more viral DNA than do those from the throat1. The lesions appear to be comparatively “virus-ridden,” says Boghuma Titanji, an infectious disease physician at Emory University in Atlanta, Georgia, who was not involved in the study.

various studiestwo,3, including that of Mitjà, show that few people contract the disease from an infected household member with whom they did not have sexual contact. This finding, along with data on viral load, suggests that respiratory droplets and airborne particles are probably not the main route of transmission, says Titanji. If corroborated by more research, it could raise questions about whether people should be isolated for the full duration of the infection, which could be difficult because the illness seems to take up to a month to resolve, she adds.

Detailed data on how a person’s viral load changes over time is still lacking, says Jessica Justman, an infectious disease physician at Columbia University in New York City. Although Mitjà and his colleagues did not detect much viral DNA in the samples they collected from people’s throats early in the infection, it is possible that if they had collected them later, or even earlier, the viral levels could have been higher, she says. Such data, which the team is now collecting in a follow-up study, would allow public health officials to offer better isolation and treatment guidance to infected people.

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talking about sex

It is not yet clear whether monkeypox is sexually transmitted in absolute terms (passed from one person to another through blood, semen, or other bodily fluids during sexual intercourse). But several studies have found that monkeypox virus DNA is present in a person’s semen for weeks after they become infected.two,3. One study also isolated infectious virus from the semen of a single individual six days after symptoms appeared.4.

Even if the virus can be transmitted sexually, it is unclear what role this mode of transmission plays, compared to simply being in close skin-to-skin contact with a person or inhaling their respiratory particles, which also occur during sexual intercourse. If other tests find infectious virus in semen, it will be important to understand how long it can persist in that body fluid. Viruses like Ebola can persist in semen for months, if not years, after infection, which has complicated efforts to prevent outbreaks. Until researchers know more, the UK Health Security Agency recommends that people continue to use condoms for eight weeks after infection.

Mitjà and her colleagues noted that, in the people they examined, having more lesions in the mouth and throat was linked to oral sex, and having more lesions in and around the anus was linked to receptive anal sex. Given all of these findings, Titanji says it’s crucial that public health officials don’t shy away from talking about sex in their counseling and are explicit about the kinds of protections available.

More data from rigorously designed studies can’t come fast enough, Justman says. Some researchers are already concerned that the outbreak may already be past the point of being contained, given the news of inadequate vaccine stocks Y inaccessible antiviral treatmentsas much as insufficient evidence. Funding and motivation to study monkeypox are limited compared to COVID-19, she says. “We don’t have ‘Operation Warp Speed,'” like the one there was to speed up US vaccine development during the pandemic, she adds.

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