New study suggests possible disease vector: germ dust

For the past a few years, until the pandemic struck, Bill Ristenpart, a chemical engineer at UC Davis (and a senior coffee connoisseur), had brought a team of researchers and cases of expensive instruments across the country every been in New York and in the laboratory of Nicole Bouvier. Infectious doctor and researcher at Mount Sinai Hospital, Bouvier studies respiratory viruses, influenza A in particular. Ristenpart’s specialty is fluid dynamics. In the case of influenza, this means measuring how physical properties like temperature, humidity, and wind speed affect the flight of respiratory bloblets that fly out of the nose and mouth of humans and rodents. Together, with dozens of guinea pigs and nearly $ 2 million from the National Institutes of Health, they hoped to unravel a century-old mystery: Why is there a flu season?

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They still don’t know that. Instead, their work revealed compelling evidence that some respiratory viruses, at least in laboratory animals, don’t always travel through droplets of liquid, as scientists have long assumed. Infected guinea pigs don’t just breathe or sneeze bits of the flu. They can actually launch infectious particles into the air from their fur, paws, and cages.

Remember the “fomites”, those germ deposits on surfaces that led to so much washing and wringing of hands in contact with the face during the first days of the pandemic? Well, sometimes rather than settling on big things like tables and cellphones germs stick to the surface of solids that are so small you can’t even see them like microscopic fibers, cells. dead skin and dust. These tiny solids can then be blasted into the air. When they do, Bouvier and Ristenpart call them “aerosol fomites”. And according to their research, these germ particles can make other animals sick. In fact, in their latest study, aerosolized fomites appeared to be the primary means of influenza transmission from their guinea pigs.

“Our experiments show very clearly that when guinea pigs move around, they stir up dust. And if this dust is contaminated with a virus, it can transmit it by air to another animal in a separate cage, ”explains Ristenpart. Their work also raises the possibility that this fourth route of transmission – aerosol fomites – may also have significance for human health, he says. Especially during a global epidemic of a new respiratory virus. “When you rub your face, brush your shirt, or crumple a piece of tissue paper, you spray particles on a micron scale,” says Ristenpart. “And if that surface had ever been touched by mucus containing a virus, then you are also an aerosolized virus that other people can inhale.”

The UC Davis / Mount Sinai team published the findings in the newspaper on Tuesday that shake up the assumptions Communications of nature. Although the experiments were conducted before the pandemic and with an influenza virus, their results now land amid a heated dispute over the transmission of the novel coronavirus SARS-CoV-2. At the heart of the controversy is the disagreement over the size, behavior and relative importance of the droplets that infected people emit from their airways – particularly, whether these expiratory particles can travel long distances and remain in suspension for long periods of time. long periods. Now this study adds a new wrinkle. What about viral particles released into the air through other routes – lifted off the floor, shaken off a bedspread, crumpled up on dirty fabric? How much do people have to care this?

The answer – for now at least – is probably more than a little bit, says Richard Corsi, dean of engineering and computer science at Portland State University, who was not involved in the study. Now a director, Corsi has spent decades studying indoor air quality. He observed that people constantly change their surroundings with their movements, both removing skin and fiber from clothing and disturbing clouds of particles in the ground. Some scientists have even been able to measure the unique microbes that live in these personal aerosol clouds. So it’s no surprise that viruses can hitchhike in the same way as other microbes. “I think this article strongly suggests that we shouldn’t go down the path of resuspending fomites from surfaces,” Corsi says. “That doesn’t mean it’s the most important transmission route. But it is a way.