Tuesday, January 26, 2021

Smoke from forest fires is loaded with microbes. Is it dangerous?

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If you are unhappy enough to breathe in the smoke of forest fires, you get a whiff of charred plant material, noxious gases, and – if the fire tears apart human structures – cremated synthetics. In all areas, these are bad things, which turned out to be serious harm to human health, especially for people with respiratory problems such as asthma. And not to pile on the worries, but this haze is also found to be loaded with microbes like bacteria and fungi.

The problem is, scientists are just starting to study this smoky microbial community. This led two researchers to publish a new perspective piece in the newspaper Science today calling for multidisciplinary action to better characterize these microbes and determine how they might make wildfire smoke worse for human lungs. “It’s not only made up of particles and gas, but it also contains an important living component,” says Leda Kobziar, University of Idaho fire scientist, co-author of the article. Smoke from forest fires can actually spread organisms beneficial to an ecosystem, adds Kobziar, but “what could be the consequences of spreading pathogens that we know are airborne?”

But wait for a tick: Shouldn’t germs be cooked to death in flames? Now, that doesn’t give those germs no credit. You see, a forest fire burns with different intensities in different places as it moves through a landscape. “At the smallest scales, complete combustion is associated with incomplete combustion,” Kobziar explains. “Even at one centimeter you could get very high temperatures for long periods of time, and the next centimeter it can be completely ignored, and no heat at all. This degree of variability therefore provides many pockets in which these microbes could survive fire.

Instead of perishing, they hitchhike on chunks of charred carbon and water vapor, as the heat of the wildfire propels all the mud skyward. If they end up in tiny water droplets, it may well protect them from desiccation as they move downwind. “We know that microbes attached to dust particles are definitely transported across continents,” Kobziar says. “So we have no reason to believe that this does not also happen in smoke when the smoke moves. But how long do they survive and which do they survive? That’s an open question, and that’s exactly the kind of research we hope this paper will inspire.

Take, for example, the mushroom genus Coccidioides, whose species live in the soil. When a fire rips through a landscape, it disturbs the ground both directly, chewing it with flames, but also indirectly: all this hot, rising air creates an atmospheric vacuum near the surface, and more air enters through the sides to fill. he. This can produce strong winds that scour the earth, pulverizing the fungi.

When firefighters inhale this rotten air, the fungi can lead to a disease called coccidioidomycosis, or valley fever, with symptoms such as fever and shortness of breath. The condition can progress to cause pneumonia or meningitis, an infection of the tissues surrounding the brain and spinal cord. (Infection with another kind of fungus called Cryptococcus, also a concern in smoke from wildfires, leads to similar symptoms.) Coccidioidomycosis is common enough among firefighters that the Centers for Disease Control and Prevention considers the profession at risk for fungal infection.

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As forest fires get bigger and more intense thanks to climate change, researchers are seeing a worrying increase in cases of yeast infection (that is, any disease caused by a fungus) in the American West. Fungal spores “can act as an allergen and initiate the development of asthma in the atopic population and have been associated with decreased lung function, hospitalizations and increased mortality,” says Mary Prunicki, director of research on air pollution and health to Sean N. Parker of Stanford University. Center for Allergy Research, which was not involved in this new document. “Overall, there are many microbes of concern for human health.”

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