Q&A: Wildfire smoke may carry bacteria, fungi
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Wildfire smoke can transport bacteria and fungi, making it a potential vehicle for infectious agents, according to an article published in Science.
“Given that climate change impacts on wildfire are predicted to lead to total emissions (greenhouse and trace gases plus particulate matter) increases of 19% to 101% in California alone through 2100, it is important that atmospheric and public health sciences expand their perspectives to include the potential impact of smoke’s microbial cargo on human populations,” 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 Infectious Disease News Editorial Board Member George R. Thompson III, MD, associate professor of medicine at the University of California, Davis, wrote. “This is especially relevant where smoky skies are more likely to be a seasonal norm rather than a rare event.”
Wildfires are a source for bioaerosols composed differently from those under “background conditions,” making most of the microbes in wildfire smoke “viable,” they wrote.
We spoke with Kobziar about the infectious disease-related threat that smoke may pose in regions affected by wildfires.
Q: Have there been any documented cases of wildfire smoke directly infecting a patient?
A: We don’t have any documented cases. Determining whether smoke was the source of an infection will be a challenge until we know better whether infectious agents are in the smoke in high enough concentration to reach communities at known distances from a fire. This is where smoke and fire behavior modeling will intersect with microbiology and infectious disease.
Q: What findings from this report should the general public be aware of?
A: This article presents findings that have been published in the last couple of years that show that smoke has a significant number of living microbes in it. We know that particulate matter and smoke is responsible for affecting human health, and we also now know that particulate matter is associated with microbial content in smoke. What we are doing in this article is connecting those two lines of research with the hope of illuminating some of the patterns that epidemiologists have seen with regard to infections and their distribution across time and space.
Q: What types of microbes are capable of surviving the extreme heat of wildfire smoke?
A: The first thing that is important to recognize is that temperatures in smoke plumes are highly variable and frequently fluctuating. Smoke columns are always interacting with the ambient air around them, which tends to be somewhat cooler. The high degree of mixing with ambient air means that the temperatures of the column could vary quite far 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 are thereby afforded some protection from excessive heating.
Finally, many of these organisms are likely tolerant of the temperatures that are higher than what might be considered their biological threshold, as long as they don’t experience those temperatures for very long. So, the high degree of variability is both spatial and temporal, and we think that makes a difference in enabling these microbes to survive in the smoke column.
Q: What areas of this topic warrant further research?
A: The fact that we have found so many organisms that are not typically found in ambient conditions or in the air around us that we breathe in every day warrants further investigation. It suggests that through the combustion process (which of course involves both physical and chemical degradation of biotic materials) the physical breakdown may expose organisms that would not otherwise be exposed to convective updrafts or other types of wind-inducing events.
The next steps regarding human health are to specifically test for, both in the field and laboratory, the presence of pathogenic microbes and to assess their concentration. In the field, we can then test how far they are transported in the context of certain types of fire behavior. Higher intensity fires are likely to transport not only more materials and organisms but to transport them further as well. These are all very exciting areas for further investigation.
Q: How common do you suspect this phenomenon is and what should clinicians/physicians be aware of?
A: We have no reason to believe that the phenomenon of wildland fire aerosolizing microbes as a component of the smoke is not happening everywhere that wildland fires are happening. That means that the ramifications of this line of work are global. This also means that there is the potential the infections are being caused in areas outside of where specific pathogens are endemic. What I would recommend is that during and even weeks after smoke inundation events, clinicians think broadly about the potential causal agents of any respiratory infections they see, and not limit their testing to those organisms that are known to be endemic for the region.
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