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Wildfires escalate the risk of infection by weakening the body’s immune defenses and spreading the bugs in the smoke
Jan
Over the past few days, the world has watched in shock as wildfires devastated vast areas of Los Angeles.
Beyond the obvious destruction – landscapes, homes, businesses and more – fires on this scale have far-reaching impacts on communities. Many of them concern human health.
We know that fire can cause direct harm, causing injury and death. Unfortunately, the death toll in Los Angeles is now high at least 24.
However, forest or bushfires can also have indirect consequences on human health. In particular, they may contribute to the occurrence and spread of a number of infections.
Effects on the immune system
Most people are aware that fires can cause burns and smoke inhalation, both of which can be life-threatening in themselves.
Perhaps less known is that both burns and smoke inhalation can cause acute and chronic illness changes in the immune system. This can expose affected individuals to infections at the time of injury and for years to come.
Causes burns profound changes in the immune system. Some parts go into overdrive, become too reactive and lead to excessive inflammation. Immediately after severe burns, this can contribute to sepsis and organ failure.
Other parts of the immune system appear to be suppressed. Our ability to recognize and fight insects can be impaired in the event of burns. Studies show that these cases occur in people who have experienced severe burns increased risk flu, pneumonia and other types of respiratory infections for at least the first five years after injury compared with people who had not experienced burns.
Wildfire smoke is a elaborate mixture containing particulate matter, volatile organic compounds, ozone, toxic gases and microorganisms. When people inhale smoke during wildfires, each of these elements can play a role in increasing inflammation in the airways, which can lead to increased susceptibility to respiratory infections and asthma.
Research published after the 2019–2020 Australian Black Summer found that: higher risk of Covid infection in areas of Up-to-date South Wales where bushfires had occurred a few weeks earlier.
We need more research to understand the scale of this increased risk and its duration persist after exposureand mechanisms. However, these effects are thought to be due to persistent changes in the immune response.
Microorganisms move in smoky air
Another possibility of infection arises from fire-induced movement of microorganisms from the niches they usually occupy in soil and plants in natural areas to densely populated urban areas.
Recent evidence from Utah wildfires shows that microbes such as bacteria and fungal spores may be the cause transported in smoke. These microorganisms are associated with particles from a source such as burned vegetation and soil.
There are thousands of different ones species of microorganisms in smokemany of which are not common in the background, smoke-free air.
So far, only a diminutive amount of research has been published on this topic, but researchers have demonstrated the majority microbes in smoke are still alive AND stay alive in the smoke long enough to colonize the places where they eventually land.
How far specific microbes can be transferred remains an open question, but fungi have been detected associated with smoke particles hundreds of miles even downwind from the fires weeks after the fire.
Read more: Los Angeles wildfires: Long-term exposure to wildfire smoke is poorly understood and risks are rising
Does this cause infections in humans?
A subgroup of these airborne microorganisms is known cause infections in humans.
Scientists are examining records of fungal infections in humans due to exposure to wildfire smoke. In particular, they look at soil-borne infectious agents such as mushrooms Merciless coccidioids AND Coccidioides posadasii which thrive on dehydrated soils and can be captured as dust and smoke.
These fungi cause valley feverlung infection with flu-like symptoms, all dehydrated western parts of the United States.
A study of California wildland firefighters found high rate of valley fever infectionwhich prompted occupational health warnings, including recommendations on the employ of respirators in endemic regions.
A study conducted in California on a broader population found that: 20% increase in hospital admissions in the case of valley fever after any amount of exposure to wildfire smoke.
However, only another one was found limited evidence of excess cases following smoke exposure in populations adjacent to wildfires in California’s San Joaquin Valley.
These contrasting results show more research is needed to assess the infectious potential of wildfire smoke from this and other fungal and bacterial causes.
Jae C. Hong/AP/AAP
Security
Much remains to be learned about the links between wildfires and infections, and about the many pathways through which wildfires may escalate the risk of certain infections.
There is also a risk that people gathering together after such a disaster, for example in potentially overcrowded shelters, could escalate the transmission of infections. We saw this happen later previous natural disasters.
Despite gaps in our knowledge, public health responses to wildfires should include infection prevention (e.g., by providing effective masks) and surveillance to enable early detection and effective management of any outbreaks.
