Over the past several days, the world has watched on in shock as wildfires have devastated large parts of Los Angeles.
Authors
- Christine Carson
Senior Research Fellow, School of Medicine, The University of Western Australia
- Leda Kobziar
Professor of Wildland Fire Science, University of Idaho
Beyond the obvious destruction – to landscapes, homes, businesses and more – fires at this scale have far-reaching effects on communities. A number of these concern human health.
We know fire can harm directly, causing injuries and death. Tragically, the death toll in LA is now .
But wildfires, or bushfires, can also have indirect consequences for human health. In particular, they can promote the incidence and spread of a range of infections.
Effects on the immune system
Most people appreciate that fires can cause burns and smoke inhalation, both of which can be life-threatening in their own right.
What’s perhaps less well known is that both burns and smoke inhalation can cause acute and chronic . This can leave those affected vulnerable to infections at the time of the injury, and for years to come.
Burns induce . Some parts go into overdrive, becoming too reactive and leading to hyper-inflammation. In the immediate aftermath of serious burns, this can contribute to sepsis and organ failure.
Other parts of the immune system appear to be suppressed. Our ability to recognise and fight off bugs can be compromised after sustaining burns. Research shows people who have experienced serious burns have of influenza, pneumonia and other types of respiratory infections for at least the first five years after injury compared to people who haven’t experienced burns.
Wildfire smoke is a complex mixture containing particulate matter, volatile organic compounds, ozone, toxic gases, and microbes. 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 .
Research published after Australia’s Black Summer of found a in areas of New South Wales where bushfires had occurred weeks earlier.
We need more research to understand the magnitude of these increased risks, how long they , and the mechanisms. But these effects are thought to be due to sustained changes to the immune response.
Microbes travel in smoky air
Another opportunity for infection arises from the fire-induced movement of microbes from niches they usually occupy in soils and plants in natural areas, into densely populated urban areas.
Recent evidence from forest fires in Utah shows microbes, such as bacteria and fungal spores, can be . These microbes are associated with particles from the source, such as burned vegetation and soil.
There are thousands of different , many of which are not common in background, non-smoky air.
Only a small number of studies on this have been published so far, but researchers have shown the majority of and long enough to colonise the places where they eventually land.
How far specific microbes can be transported remains an open question, but fungi associated with smoke particles have been detected downwind from wildfires, even .
So does this cause human infections?
A subset of these airborne microbes are known to .
Scientists are probing records of human fungal infections in relation to wildfire smoke exposure. In particular, they’re looking at soil-borne infectious agents such as the which thrive in dry soils that can be picked up in dust and smoke plumes.
These fungi cause , a lung infection with symptoms that can resemble the flu, across arid .
A study of wildland firefighters in California showed , which spurred occupational health warnings including recommended use of respirators when in endemic regions.
A California-based study of the wider population showed a for valley fever following any amount of exposure to wildfire smoke.
However, another found only after smoke exposure in wildfire-adjacent populations in California’s San Joaquin Valley.
These contrasting results show is needed to evaluate the infectious potential of wildfire smoke from this and other fungal and bacterial causes.
Staying safe
Much remains to be learned about the links between wildfires and infections, and the multiple pathways by which wildfires can increase the risk of certain infections.
There’s also a risk people gathering together after a disaster like this, such as in potentially overcrowded shelters, can increase the transmission of infections. We’ve seen this happen after .
Despite the gaps in our knowledge, public health responses to wildfires should encompass infection prevention (such as through the provision of effective masks) and surveillance to enable early detection and effective management of any outbreaks.
