Fungi are learning to adapt to climate change, posing a major threat to human health.

Fungal infections range from minor conditions, such as athlete’s foot, to life-threatening respiratory diseases and bloodstream infections.

Fungi are known for their ability to adjust to – and thrive in – new and changing environments.

Now, they are learning to adapt to the rising temperatures, changing rainfall patterns and extreme weather events that characterise a warming planet.

This is increasing their ability to colonise and cause disease in the human body.

However, there is a severe lack of diagnostics, treatments and vaccines available for fungal infections – and fungal resistance to existing drugs is on the rise.

An increase in fungal infections driven by climate change could also have devastating consequences for agriculture, damaging crops and threatening food security.

New fungal pathogens

Fungi are one of five “kingdoms” of life on Earth – putting them in a distinct category separate from animals or plants.

There are millions of fungal species – from saccharomyces cerevisiae, or baker’s yeast, to penicillium chrysogenum, which is the source of the antibiotic penicillin.   

Fungal infections can be transmitted to humans through direct contact in the environment, with contaminated surfaces or via infected individuals.

Historically, most fungi do not cause disease in humans, meaning they are not “pathogenic”.

This is because – unlike viruses and bacteria – most fungi cannot survive or spread in body temperatures of 37C.

But, as global temperatures rise, some fungi are adapting to survive in hotter environments, including the human body.

(How fungi adapt to their environments is still not fully understood. However, their large genomes and diverse metabolic pathways – the chemical reactions which allow organisms to function – are thought to play a key role in their ability to survive and grow in a wide range of conditions.)

An example of this is candida auris, a fungal infection that emerged simultaneously on three continents in the late 2000s. The fungus mostly infects people with weakened immune systems and is a real concern as it can cause bloodstream infections. It is a serious problem in intensive care units, where the fungus sticks to medical equipment and grows rapidly. 

Many infection, prevention and control measures are unable to get rid of it. Candida auris is already resistant to several antifungal drugs, making it very challenging to treat. One study in Oman, for example, recorded a fatality rate over more than 50%.

Due to lack of surveillance and routine monitoring, we do not know exactly how many people are impacted by candida auris infections.

To address this, the World Health Organization Global Antimicrobial Resistance and Use Surveillance System (WHO-GLASS) – a programme that provides a standardised approach to collect and analyse data for antimicrobial resistance surveillance – has included a protocol for candida auris. 

Candida auris is one of four fungal species identified by the World Health Organization (WHO) as a “critical” threat to public health, alongside aspergillus fumigatus, candida albicans and cryptococcus neoformans. 

Scientists have pointed to the likelihood that the emergence of candida auris is being driven by rising temperatures caused by climate change. 

A 2022 study noted that higher temperatures driven by human-caused climate change may have added “selective pressure” on candida auris – leading to the spread of strains “adapted to salinity and higher temperatures – similar to the conditions found in the human body”.

The emergence of candida auris is just one example of how climate change is exacerbating fungal infection.

A study currently undergoing peer review suggests that – without effective strategies to tackle climate change – the aspergillus family could expand its reach to more northerly swathes of Europe, Asia and the Americas, exposing more people to life-threatening respiratory infections as temperatures rise.  

Aspergillus infections can cause permanent damage to lungs and lead to serious illness in individuals with existing respiratory conditions or weakened immune systems.

Extreme weather

Rising temperatures are not the only cause of rising fungal infections linked to climate change.

Changing rainfall patterns, increasing humidity and worsening extreme weather events are also driving fungal pathogens to new areas. 

Heavy rainfall, flooding and humidity leads to increased moisture in homes, increasing the growth of indoor mould. Mould – which encompasses a diverse group of fungal species – can cause substantial health impacts when inhaled for those with underlying health conditions, such as asthma. 

Meanwhile, extreme weather events, such as wildfires and floods, transport fungal pathogens to new regions by spreading spores far beyond where they would typically be found. This increases the threat fungi pose to both human health and agriculture.

For instance, the fungus coccidioides, which is found in soils in the south-western US and parts of central and South America, causes valley fever – a lung infection which can be fatal to humans and animals. 

Outbreaks occur when extreme events, such as wildfires, disturb large amounts of soil and spread fungal spores into the air. These enter the human body when inhaled. Cases are often unreported, but it is estimated that the fungi causes around 206,000-360,000 cases per year in the US. 

The fungus thrives in a hot and dry climate. Coccidioides is now being seen in regions that would not normally support its growth, as the climate heats up.  

A 2019 study used climate models to project that the range of valley fever could expand into more northerly US states such as Idaho, Wyoming and Nebraska. It also estimates that, by 2100, cases across the US could rise by approximately 50% as more regions develop climates suitable for transmission.

Threatening food security

Fungal pathogens also threaten human health indirectly by damaging harvests and causing a range of plant diseases, including blights, root rot and mildew.

Fungi are a key part of soil ecosystems, but plant pathogenic fungi can cause growers to lose between 10-23% of their crops every year – and a further 10-20% after they are harvested, as food that is incorrectly stored goes mouldy at different points of the supply chain.

Rising temperatures can spread and introduce more pathogens to an area, which can reduce harvests and, in some cases, wipe out entire crop families. This could result in food insecurity globally and economic instability in regions that rely on agricultural exports. 

Modern agriculture’s reliance on growing genetically uniform crops, known as monocultures, puts the global food system at increased risk of fungal disease, as pathogens learn how to colonise crops.

Developments in the global banana market are a prominent example of the threat posed by fungus to crops. In the 1950s, the Gros Michel banana – once the main export variety of banana – was wiped out by a disease caused by the fungus fusarium oxysporum.

Now, the banana variety that was grown and exported in its place – the Cavendish banana – is under threat by a new strain of fusarium. This poses a major threat to the global banana trade, given that the Cavendish banana accounts for 47% of banana production and virtually all bananas supplied to the US and Europe.

In another example, the fusarium graminearum fungus, which flourishes in wet conditions and warm temperatures, causes a disease that is thought to cause wheat and barley yield losses amounting to more than $1bn every year.

Rising antifungal resistance

The spread of fungal infections caused by climate change is particularly concerning given the lack of available treatment options, as well as limited awareness among the public and healthcare professionals.

Most healthcare professionals receive little training around how to identify fungal infections, leading to delayed diagnosis and treatment. In the developing world, fungal infections can be deadly because both awareness and access to diagnostic tests are lacking.

There are just four types of antifungal drugs and no approved fungal vaccines.

Antifungal treatments are harder to develop than antibiotics because fungi are more biologically similar to humans than plants – making them difficult to kill without harming human cells.

Meanwhile, resistance to the antifungal drugs that are available is growing.                                                                                           

The fungicides used to kill fungi in agriculture often share “modes of action” with medical antifungals. The overuse of these fungicides has led to fungi in the environment building up their resistance – creating hardier fungi that are more difficult to treat in clinical settings. 

As climate change puts additional stress on the food system, the risks and benefits of using fungicides to ensure food security need to be balanced with safeguarding the effectiveness of antifungal drugs.

However, there is limited communication between agricultural and medical sectors around how to juggle these priorities.  

And yet – despite all these challenges – fungal infections receive a fraction of the funding and attention that bacterial or viral diseases do. 

Fungi that tackle climate change

Fungi have historically been an asset in medical research – most notably the discovery of the drug penicillin. They could also prove valuable in the fight against climate change.

Some fungi are used to suppress populations of pests or pathogens in agriculture. This method – known as natural biocontrol – uses fungi, or other forms of naturally occurring organisms – such as bacteria, insects or viruses – as a replacement for chemical pesticides.

Natural biocontrol is seen as a more environmentally friendly method for treating crops than manmade chemicals because the organisms break down naturally in the environment and do not leave toxic residues in the soil. 

Meanwhile, researchers have also found that mycorrhizal fungi – which grow in association with plant roots – store roughly 13bn tonnes of carbon (GtC) – equivalent to 36% of annual  global fossil fuel emissions. The fungus does this by absorbing carbon from plants and locking it in their underground networks and soil, where it stays stable for long periods. 

There are groups looking at how the mycorrhizal fungi could be harnessed to help deliver decarbonisation – similar to tree planting. 

However, more research is needed to better understand the valuable properties of fungi, including how they could be part of “nature-based solutions” to help tackle climate change.

Discovering the unknown

There is still a lot that remains unknown about fungi. Scientists estimate that less than 10% of all species have been identified globally.

Fungi are essential to healthy ecosystems. They recycle nutrients by breaking down organic matter and play a critical role in the carbon cycle.

But climate change is disrupting this balance. Rising temperatures and environmental shifts threaten to wipe out some fungal species before they’re even discovered, while enabling others to thrive in new – and often harmful – ways. 

These changes signal deep trouble for the natural world.

It is, therefore, critical that more scientific attention is paid to the risks and opportunities of fungi as they learn to adapt to a warmer climate. 

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The post Guest post: Fungal infections are adapting to climate change – and threatening public health appeared first on Carbon Brief.

Guest post: Fungal infections are adapting to climate change – and threatening public health