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Forest fires throw microbes into the air. What is the health risk?


As climate change brings more forest fires to the western United States, a rare fungal infection has also been on the rise. Valley fever is more than six times higher in Arizona and California between 1998 and 2018, according to the U.S. Centers for Disease Control and Prevention.

Valley fever causes cough, fever, and chest pain and can be fatal. Guilty fungi, members of the genus Coccidioides, thrive in soils in California and the southwestern desert. Firefighters are especially vulnerable to the disease. Forest fires seem to remove and send into the air the soil-loving fungi, where they can enter people’s lungs.

If fires are helping these disease-causing fungi to move, could they be sending other microorganisms as well? Leda Kobziar, a fire ecologist at the University of Idaho in Moscow, decided in 2015 to see if she knew if and how microorganisms such as bacteria and fungi are transported by smoke from forest fires, and what that could mean for human and ecological health .

In 2018, Kobziar launched a new field of research he called “pyroaerobiology”. First, he asked if microorganisms can survive the scorching heat of a forest fire. The answer, he found, is yes. But how far bacteria and fungi can travel through the wind and how many are two of the many great unknowns.

With a recent push to spark new collaborations and research, Kobziar hopes scientists will begin to understand how important the transport of smoke from microbes can be.

For Kobziar’s first studies in 2015, his students lifted Petri dishes on long poles to collect smoky air samples near a prescribed fire in the University of Florida’s experimental forest.L. Kobziar

investigators piloting a drone over a prescribed burnToday, Kobziar and colleagues use drones to collect samples in the experimental forest of the University of Florida.L. Kobziar

Invisible but penetrating

The air may seem clear, but even in the cleanest air, “hundreds of different bacteria and fungi blow around,” says Noah Fierer, a microbiologist at the University of Colorado Boulder.

Winds pull bacteria and fungi from all kinds of surfaces: agricultural fields, deserts, lakes, oceans. These microbes can rise into the atmosphere to travel the world. Scientists have found microorganisms from the Sahara in the Caribbean, for example.

Fierer points out that many (if not most) of the airborne microorganisms, including bacteria, fungi, and viruses. But some can get sick or cause allergic reactions, he said. Others cause disease in crops and other plants.

The billions of tons of dust that come out of deserts and agricultural fields each year act as a microbial conveyor belt. In places like Arizona, people know to be alert to symptoms of airborne diseases, such as valley fever after dust storms, as infections increase later by the wind. If dust can move living microorganisms around the globe, it makes sense that smoke particles are also engines of microbes, Kobziar says, assuming that microscopic life forms can survive a fire and a spin in the atmosphere.

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Tiny travelers

Rising temperatures and worsening droughts have led to longer and more intense forest fire seasons throughout the west (SN: 26/09/20, p. 12). Breathe smoke from sick fires (SN online: 18/09/20), even causing premature death from heart and lung disease. In the United States, wildfire causes about 17,000 premature deaths a year, a number that is projected to double by 2,100, according to a GeoHealth study conducted in 2018.

In other parts of the world, the effects are much worse. In 2015, smoke from illegal land-clearing flames and forest fires in Indonesia killed 100,000 people across Southeast Asia, according to a 2016 report in Environmental Research Letters. The fault is often attributed to particles: organic and inorganic particles suspended in the air, including pollen, ash, and pollutants. But scientists and health officials are increasingly realizing that there is much we don’t know about how smoking affects human health.

The most intense fires, the ones that burn the most and release the most energy, can create their own weather systems and send smoke into the stratosphere, which stretches about 50 kilometers above the Earth's surface (SN: 14/09/19, p. 12). Once there, smoke can travel the world just as the ashes of explosive volcanoes do. Kobziar’s team and others provided convincing evidence in the February ISME newspaper that living, living microorganisms can be transported in plumes of smoke, at least close to the Earth’s surface if not higher up.

smoke from an experimental fire flowing over the Fishlake National ForestThe Fire and Smoke Model Assessment Experiment team, or FASMEE, created this high-intensity crown fire in the poplars of Fishlake National Forest, Utah, in 2019. The team used a drone to measure microbial concentrations in this smoke.L. Kobziar

In 2015, while at the University of Florida in Gainesville, Kobziar and his students collected the first air samples for this line of research during a series of planned or prescribed burns that Kobziar fixed in the school’s experimental forest. The group arrived in the forest armed with 3-meter-long poles covered with Petri dishes to collect air samples.

Before catching fire, the team kept the Petri dishes in the air for three minutes to collect air samples as a baseline prior to the fire. Then Kobziar, manager of burns prescribed certificate (or as she calls it, a "lighter"), lit the fires. Once the flames spread at a steady pace and the smoke fell, the students raised new Petri dishes to the smoke, almost as if they were pointing a marshmallow at a stick against a campfire. This allowed them to collect smoked air samples to compare with the “before” samples.

Back in the lab, in a dark room kept at a constant temperature of 23 ° Celsius, both the baseline and the smoked Petri dishes – covered and closed with new contamination – were left for three days. The microbes began to grow. Kobziar says much more bacterial and fungal species populated the smoked Petri dishes than the base plates, indicating the fire aerosolized some species that were not in the air before the fire.

two Petri dishes with samples of smoke microbesThese Petri dishes show colonies of fungi and bacteria that grew after five minutes of exposure to smoke. The smoke came from pine needles collected in Florida and then burned in the lab at Kobziar University in Idaho.L. Kobziar

two Petri dishes with samples of smoke microbesThese Petri dishes show colonies of fungi and bacteria that grew after five minutes of exposure to smoke. The smoke came from pine needles collected in Florida and then burned in the lab at Kobziar University in Idaho.L. Kobziar

“We were amazed at how many different microbial colonies survived the combustion environment and grew in the smoke samples, compared to very few of the ambient air,” he says. Based on DNA testing, Kobziar's team identified 10 types of bacteria and fungi; some are pathogenic to plants, one is a parasite of ants and one helps plants absorb nutrients. “This was the time when the way we thought about smoke was completely transformed,” he says.

In 2017, after Kobziar moved to Idaho, his team collected soil samples from the University of Idaho’s experimental forest and burned them – this time, in the lab. As the smoke spread over the burning soils, the researchers collected air samples and again sealed them and placed them in a dark, warm room to see what would grow. After a week, many different microbes, including fungi, multiplied in colonies on the plates, the researchers reported in 2018 in Ecosphere.

Alive and moving

Since then, the Kobziar team has collected more air samples during prescribed burns of varying intensities in Florida, Idaho, Montana and Utah, joining forces with the Forest Fire and Smoke Model Evaluation Experiment or FASMEE team. For the safety of his students, he replaced the poles and Petri dishes with drones. It sends a single drone carrying a vacuum pump with a filter in plumes of smoke at varying altitudes of up to 120 meters, according to equipment described in Fire magazine in 2019.

The FASMEE team has set up a mobile research laboratory on the line of fires in the Fishlake National Forest. Drone operators sent the machines to the smoke to collect samples, back to the “lab” to return the samples, and then back up to collect more several times. They found about 1,000 different types of microbes in the smoke.

In each experiment, researchers found live bacteria and fungi, many of which were not found in any of the air samples taken before the fires. In Utah smoke samples, for example, the FASMEE team found more than 100 different fungi that were not in the air before the fire, Kobziar says. Among the findings were Aspergillus species, which can cause fevers, coughs and chest pain, as well as Cladosporium, molds that can cause allergies and asthma.

It is unknown if any of these microorganisms pose a danger to humans, Kobziar warns. His team has not tested whether microbial species that survive heat can cause disease, but the group plans to do so.

Research in Utah has revealed another crucial fact: these microbes are tough. Even in smoke from high-intensity, high-temperature fires, about 60 percent of bacterial and fungal cells are alive, Kobziar says. About 80 percent appear to survive lower-intensity fires, which is "about the same percentage of cells we would expect to see alive in ambient air conditions," he says. Thus, these early studies show that fires send live bacteria and fungi into the air. And that they can travel at least 120 meters above the ground and about a mile from a flame front.

But there are still many basic questions left, Kobziar says. How do microbes change – in quantity, type or viability – depending on the distance traveled away from the flames? How far can they go? How do microbial releases affect different sources of fuel – pines, grasslands, deciduous trees or crops, for example? How does it affect the intensity of the fire at which it is released and how far it travels? Does the type of combustion (which smokes (like a wet log in a campfire) in the face of high-intensity fires) affect what is released? How does temperature, humidity, or weather affect microbial survival?

So, of course, Kobziar has many questions about how to conduct this new field of research: what are the best and safest ways to test the air in the dangerous environment of an unpredictable forest fire? How to avoid contamination of biological samples?

He has been learning as he goes, perfecting his methodology. The answers to many of those questions could come if one of Kobziar’s dream collaborations comes true: he wants to work with researchers whose studies include NASA’s DC-8 “flying lab,” which explores the Earth’s surface and atmosphere for studies that go from archeology to volcanology.

Researchers have already tracked many chemicals released by fire in the stratosphere from the Arctic to the South Pacific and throughout the environment, using the DC-8 for NASA's atmospheric tomography mission, says Christine Wiedinmyer, a modeler of fire emissions from the Cooperative Institute for Research in Environmental Sciences in Boulder, Colorado. Finding traceable fire signatures everywhere in the atmosphere suggests that fires could also send bacteria and fungi around the world, she says.

thunder clouds over smoak cloudsNine miles above the Earth's surface, a camera from NASA's DC-8 flying lab took this image of thunderstorm clouds rising above the columns of smoke from a fire in eastern Washington on August 8, 2019. Such storms, formed by intense fires, high particles, chemicals, and perhaps even microbes into the stratosphere.David Peterson / EE. UU. Naval Research Laboratory

“Pyroaerobiology is so great,” says Wiedinmyer, who tracks and simulates the movement of chemicals in fire smoke around the world. He sees no reason why such models of atmospheric chemistry could not be used also to track and predict the movement of microbes in smoke feathers, once researchers gather sufficient measurements. These data can answer basic questions about the dangers to human health of microorganisms in smoke.

Microbiologist Fierer in Boulder and Wiedinmyer collaborated in sampling and modeling chemistry. Both plan to move to bacterial and fungal modeling using data. Fierer is gathering microbial concentrations in the smoke of forest fires.

Meanwhile, Kobziar works with atmospheric modelers to figure out how to model the movements of microbes in smoke. The long-term goal is to develop models to supplement current air quality forecasts with warnings of air quality problems in the United States related to microorganisms released by forest fires in smoke.

A map of the United States

While Kobziar’s team focuses on measuring microbes in smoke, Fierer’s team is working to get a baseline of what microbes are in the air in different places during normal hours and then compare the baseline with smoke. The group has been taking indoor and outdoor air samples in hundreds of homes in the United States to "trace what microbes we breathe as we go about our daily business," says Fierer. They are also taking air samples in Colorado, which experienced record fires in 2020 (SN: 19/12/20 and 1/2/21, p. 32).

Fierer's team uses sampling stations with small, high-power vacuum cleaners on top of 2-meter-high poles to "test air for a period of time without smoke. Then boom, smoke (the site), we test for a few days when there is smoke in the air and then we also try afterwards, ”says Fierer. Analyzing samples from before, during, and after a fire is ideal, he says, as there is a huge variation in microbial and fungal populations in the air. Near a midwestern city in winter, for example, microorganisms may include those associated with local trees or, strangely, dog feces; near a Colorado cattle lottery in the summer, microbes may include those associated with cattle feces.

Joanne Emerson is on top of a tower with her back to the cameraJoanne Emerson, then a postdoctoral researcher at the University of Colorado Boulder, shows the air above a 300-meter-high tower at the Boulder Atmospheric Observatory.N. Fierer

When the team gets its results – the pandemic has delayed data collection and analysis – Fierer says: "We will know the amount and type of microbes found in forest fire smoke compared to paired smokeless air samples and whether those microbes they are viable. ”At least in Colorado. Once scientists get measurements of how many microbes can be transported in the smoke and at what altitudes, Fierer's group can combine that information with global smoke production numbers to arrive at "some post-envelope calculations" of the volume of microbes traveling. in plumes of smoke. Finally, he says, scientists could find out how many are alive and if that even matters to human health, still "a pending issue."

Fierer and Kobziar could make big leaps forward if more scientists become involved in research. This research needs a truly multidisciplinary approach, with the collaboration of microbiologists, forest ecologists, and atmospheric scientists, Fierer says. Doing it alone “would be like having a microbiologist study microbes in the ocean and know nothing about oceanography,” he says. Fortunately, after Kobziar and the infectious disease physician George Thompson of the University of California, Davis published a call-to-arms article in Science last December, summarizing his research on pyroerobiology and noting key questions, several researchers from different fields his interest in researching the subject. “That’s exactly what we expected it to happen,” Kobziar says.

Is there danger?

In recent years, Thompson has experienced a substantial increase in patients with valley fever and other fungal infections after nearby wildfires. He was well aware that when smoke particles penetrate the lungs, they can cause breathing difficulties, pneumonia and even heart attacks. In fact, scientists reported in the Journal of the American Heart Association in April 2020 that exposure to heavy smoke during wildfires 2015-2017 in California increased the risk of heart attacks by as much as 70 percent.

He began to wonder if California’s record hells stirred other microbes along with the fungus that causes Valley fever. So he joined forces with Kobziar.

The link to Valley fever seems real, but so far local. For example, after the 2003 Simi fire burned Ventura County, more than 70 people fell ill with fever in the valley. No one knows if Coccidioid fungi can travel to get sick at a distance from the fire.

There are ways to find out if more people, local or more remote, are sick with bacterial or fungal infections after wildfires. One way, Thompson says, is to examine a community’s antibiotic prescriptions and hospitalizations in the month before and the month after a fire: more prescriptions or hospitalizations for bacterial or fungal infections after a fire could indicate a link.

In 2019 at the U.S. Transplant Congress meeting, for example, researchers linked California forest fires to an increase in hospitalizations related to Aspergillus mold and Coccidioid fungal infections.

But until we know more about what microbial fires release and where they are going, we won’t know how important that link is to human health, Fierer says.

There’s so much we don’t know yet, Thompson agrees. “We still have a lot of work to do. This is a kind of beginning of the beginning of history. "



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