Infectious Disease

Wildfire smoke can transmit micro organism and fungi

December 29, 2020

3 min read

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Wildfire smoke can carry bacteria and fungi and is a potential vehicle for infectious agents, according to an article published in Science.

“Given that the effects of climate change on forest fires are expected to increase total emissions (greenhouse and trace gases plus particulates) by 19% to 101% by 2100 in California alone, it is important that atmospheric and health sciences broadening their perspectives to include the possible effects of the microbial load of smoke on the human population ”. Leda N. Kobziar, PhD, MS, Associate Professor of Wildland Fire Science and Director of the Master of Natural Resources program at the University of Idaho, and a member of the editorial board of Infectious Disease News George R. Thompson III, MD, Associate Professor of Medicine at the University of California, Davis, wrote. “This is especially relevant when smoky skies are a seasonal norm rather than a rare occurrence.”

Forest fires are a source of bioaerosols that differ from those under “background conditions,” which makes most of the microbes in forest fire smoke “viable,” they wrote.

We spoke with Kobziar about the infectious disease threat that smoke can pose in areas affected by forest fires.

Q: Have there been documented cases of devastating smoke directly infecting a patient?

A: We have no documented cases. Determining whether smoke was the source of an infection will be challenging until we have a better understanding of whether there are infectious agents in smoke in concentrations high enough to reach communities known distances from a fire. Here, the modeling of smoke and fire behavior overlap with microbiology and infectious diseases.

Q: What lessons should the general public to be aware?

A: This article presents results published over the past few years showing that smoke contains significant numbers of living microbes. We know that particulates and smoke are responsible for the adverse effects on human health, and we now also know that particulates are linked to the microbial content in smoke. In this article, we combine these two lines of research with the hope of shedding light on some of the patterns epidemiologists have seen in relation to infections and their distribution over time and space.

Q: What types of microbes are viable the extreme heat of the devastating smoke?

A: The first thing to see is that the temperatures in plumes of smoke are very different and often fluctuate. Columns of smoke always interact with the ambient air around them, which tends to be a little cooler. The high degree of mixing with the ambient air means that the temperatures of the column can vary well below the biological threshold of these organisms. It is also possible that the organisms are in water droplets or water vapor in the smoke and thus receive some protection against excessive heating.

After all, many of these organisms are likely to be tolerant of temperatures higher than their biological threshold unless they experience those temperatures for a very long time. So the high degree of variability is both spatial and temporal, and we believe this makes a difference in how these microbes can survive in the column of smoke.

Q: What areas of this topic require further research?

A: The fact that we have found so many organisms that are not normally found in ambient conditions or in the air around us that we breathe in every day calls for further investigation. This suggests that through the combustion process (which of course includes both physical and chemical breakdown of biotic materials), physical breakdown may expose organisms that would otherwise not be exposed to convective updrafts or other types of wind-inducing events.

The next steps in relation to human health are to specifically test for the presence of pathogenic microbes, both in the field and in the laboratory, and assess their concentration. In the field we can then test how far they are transported in relation to certain types of fire behavior. Higher intensity fires are likely not only to move more materials and organisms, but also to move them further. These are all very exciting areas for further investigation.

Q: How often do you suspect this phenomenon and what should clinicians / doctors look out for?

A: We have no reason to believe that the phenomenon of aerosolization of microbes from forest fires as a component of smoke does not occur wherever forest fires occur. This means that the impact of this work is global. It also means that the infections may be caused in areas outside of specific endemic pathogens. What I would recommend is that during and even weeks after smoke flood incidents, doctors should give careful thought to the possible causative agents of respiratory infections and not limit their tests to organisms known to be endemic to the area.

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