A fungus that can ‘eat you from the inside out’ could spread as the world heats up

Aspergillus, a type of fungi, is expanding its range as the world heats up, according to new research. Centres for Disease Control/Reuters via CNN Newsource

Infection-causing fungi responsible for millions of deaths a year will spread significantly to new regions as the planet heats up, new research predicts — and the world is not prepared.

Fungi are absolutely everywhere. A vast kingdom of organisms, from mold to mushrooms, they grow in environments such as soil, compost and water. They play an important role in ecosystems but can have a devastating impact on human health: Fungal infections kill an estimated 2.5 million people a year, and a lack of data means that number could be far higher.

Yet we are still very far from understanding them, especially how these incredibly adaptable organisms will respond to a warming climate.

A team of scientists from Manchester University used computer simulations and forecasts to map the potential future spread of Aspergillus, a common group of fungi found all over the world that can cause aspergillosis, a life-threatening disease primarily affecting the lungs.

They found certain Aspergillus species will expand their range as the climate crisis intensifies, pushing into new parts of North America, Europe, China and Russia. The study, published this month, is currently being peer reviewed.

“Fungi are relatively under-researched compared to viruses and parasites, but these maps show that fungal pathogens will likely impact most areas of the world in the future,” said Norman van Rijn, one of the study’s authors and a climate change and infectious diseases researcher at the University of Manchester.

The field has seen new attention thanks to the popular HBO television drama “The Last of Us,” which follows people trying to survive in a world where an infectious mutant fungus has turned most of the population into violent monsters. (HBO and CNN share the same parent company, Warner Bros. Discovery.)

It’s fiction, van Rijn said, but he hopes it will raise the profile of fungal infections that are killing millions in reality.

Aspergillus fungi grow like small filaments in soils all over the world. Like almost all fungi, they release huge numbers of tiny spores that spread through the air.

Humans inhale spores every day but most people won’t experience any health issues; their immune system clears them.

It’s a different story for those with lung conditions including asthma, cystic fibrosis and COPD, as well as people with compromised immune systems, such as cancer and organ transplant patients, and those who have had severe flu or Covid-19.

If the body’s immune system fails to clear the spores, the fungus “starts to grow and basically kind of eat you from the inside out, saying it really bluntly,” van Rijn said.

Aspergillosis has very high mortality rates at around 20% to 40%, he said. It’s also very difficult to diagnose, as doctors don’t always have it on their radar and patients often present with fevers and coughs, symptoms common to many illnesses.

Fungal pathogens are also becoming increasingly resistant to treatment, van Rijn added. There are only four classes of antifungal medicines available.

This all spells bad news as the climate shifts open up new areas for Aspergillus to colonize.

Aspergillus flavus, a species that tends to prefer hotter, tropical climates, could increase its spread by 16% if humans continue burning large amounts of fossil fuels, the study found. It’s predicted to push into parts of northern America, northern China and Russia.

This species can cause severe infections in humans and is resistant to many antifungal medications. It also infects a range of food crops, posing a potential threat to food security. The World Health Organization added Aspergillus flavus to its critical group of fungal pathogens in 2022 because of its public health impact and antifungal resistance risk.

Aspergillus fumigatus, which prefers more temperate climates, is predicted to spread northwards toward the North Pole as global temperatures rise. Its spread could increase by 77.5% by 2100, the study found, potentially exposing 9 million people in Europe.

Conversely, temperatures in some regions, including sub-Saharan Africa, could become so hot they are no longer hospitable to Aspergillus fungi. This could bring its own problems, as fungi play an important role in ecosystems, including healthy soils.

As well as expanding their growing range, a warming world could also be increasing fungi’s temperature tolerance, allowing them to better survive inside human bodies.

Extreme weather events such as drought, floods and heatwaves can affect fungi, too, helping to spread spores over long distances. There have been spikes in fungal disease following natural disasters, such as the outbreak after the 2011 tornado in Joplin, Missouri.

The new Aspergillus study “rightfully shines a light on the threat of fungi that dwell in our natural environment and how under-prepared we are to cope with shifts in their prevalence,” said Elaine Bignell, co-director of the MRC Centre for Medical Mycology at the University of Exeter, who was not involved in the research.

Many uncertainties remain, however, and there is still a huge amount of research to be done, she told CNN.

Despite the deadly nature of aspergillosis, there is a real lack of data on where the pathogen is in the environment and who gets infected, said Justin Remais, a professor of environmental health sciences at UC Berkeley, who was not involved in the research.

He is leading a study of more than 100 million patients across the United States, which identified more than 20,000 aspergillosis cases between 2013 and 2023. The number of cases is increasing about 5% each year, he said.

“Fungal pathogens are becoming increasingly common and resistant to treatment, and we are only beginning to understand how climate change is contributing,” he told CNN.

People are used to hearing about diseases caused by bacteria, viruses and parasites, but much less so fungal diseases, said Bignell. “There is a desperate need to reverse this trend given the lethality,” she said.

“Any of us in the future might be affected.”