Science

Smallpox can also be transmitted through the air

Last week, the Centers for Disease Control and Prevention (CDC) updated its guidelines for travelers who want to protect themselves from monkeypox. This was one of his recommendations: “Wear a mask. Wearing a face mask can help protect you from many diseases, including monkeypox. ”

On Monday night, that recommendation was dropped.

“The CDC removed the recommendation to use masks in its passenger health guidelines for monkeypox because it caused confusion,” the agency said in a statement Tuesday.

However, the agency still says that in countries where this type of smallpox is spreading, “contacts shared by home and health workers” should consider wearing masks. That guideline also applies to “other people who may be in close contact with someone who has been confirmed to have smallpox.”

The change captures a little-discussed aspect of the current outbreak of simian smallpox: the virus can be transmitted through the air, at least over short distances. Although experts have stated in various interviews that air transmission is only a small factor in the overall spread, there are no solid estimates of how much it contributes.

Since May 13, when the first case of the outbreak was reported, more than a thousand people in 31 countries have been diagnosed with the virus, and at least another thousand cases are being investigated. As of Tuesday, the United States had reported 31 cases in 12 states and the District of Columbia.

In previous outbreaks, most infections were reported in people who had close contact with an infected patient or animal. But in some cases, airborne transmission was the only explanation for the infections.

In other sections of its website, the CDC still urges patients with monkeypox to wear a surgical mask, “especially those with respiratory symptoms.” Authorities also advise people living with those infected to “consider using a surgical mouthpiece” when they come in contact with people infected with the smallpox.

Monkeypox is supposed to behave like its viral cousin, smallpox. In a 2012 review of smallpox transmission, Donald Milton, a virus expert at the University of Maryland, described several cases of airborne transmission.

It was the only plausible explanation for a smallpox outbreak in New York in 1947, he wrote, when a hospital patient apparently infected another who was seven stories away. Then, in 1970, a single person infected many others on three floors of a hospital in Meschede, Germany, due to drafts in the building.

And in 2017, scientists who studied an outbreak of monkeypox in Nigeria observed cases of transmission inside a prison and recorded the infections of two health workers who had no direct contact with patients.

Last week, the World Health Organization held a scientific conference in which several researchers discussed the various unknowns that have arisen about ape pox, including its main mode of transmission.

“It’s very ambiguous to determine the true or dominant route of transmission, and part of that can be addressed in animal models,” said Nancy Sullivan, a researcher at the National Institute of Allergy and Infectious Diseases, at the conference. “That should probably be a priority in some of the lab research.”

But in briefings with the press and the general public, health officials have not explicitly addressed the possibility of airborne transmission or the use of mouthguards for protection purposes.

And in the interviews, they emphasized the role of the large respiratory droplets that expel infected patients and reach objects or people. Monkeypox infection requires “very close sustained contact,” said Andrea McCollum, the CDC’s leading virus expert.

“This is not a virus that has been transmitted several meters away,” he said. “That’s why we have to be very careful when dealing with this.”

When asked if health officials should make the possibility of air transmission more widely known, McCollum said, “That’s a good question, and it’s something we should definitely consider in order to move forward.”

For many, the CDC’s rapid change of opinion about smallpox-covered mouthpieces reminded them of the earliest times of the pandemic when authorities denied that the coronavirus was transmitted through the air. In September 2020, the agency published a guide on airborne transmission of the virus and then abruptly withdrew it just days later.

It was not until May 2021 that the agency acknowledged that the coronavirus could “remain suspended in the air for minutes to hours.”

Most of the information on monkeypox was obtained from smallpox studies. For the past two decades, scientists have been analyzing how smallpox spreads, including its presence in small droplets called aerosols, in order to prepare for the possibility of being used by bioterrorists.

“Most people think that smallpox is usually transmitted through large droplets, but for some reason it can sometimes be transmitted through small particle aerosols,” said Mark Challberg, a virologist at the National Institute of Allergy and Infectious Diseases. .

Milton warned that planning for possible airborne transmission of smallpox was particularly important in hospitals, as precautions to prevent spread through aerosols are not universal.

As the monkeypox outbreak continues, many patients become isolated at home because their symptoms are mild. Members of those households may need to consider air transmission, experts said.

There are still many questions about monkeypox, including why the current outbreak has only produced relatively mild cases. Scientists do not know if people can transmit the virus even in the absence of symptoms, how long it has been circulating in the communities and whether it can be transmitted through semen or vaginal secretions.

There is evidence that a pregnant woman can transmit the monkeypox virus to her fetus. In an observational study of 216 patients in the largest Democratic Republic of the Congo, four out of five pregnant women had miscarriages. The researchers detected the virus and viral lesions in the fetuses.

Apoorva Mandavilli is a Times reporter and focuses on global science and health. In 2019 he won the Victor Cohn Award for Excellence in Medical Science Reporting. @apoorva_nyc


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