Infection-causing fungi responsible for millions of deaths each year are expected to spread significantly to new regions as the planet heats up, new research warns — and the world is not prepared.Fungi are found everywhere — a vast kingdom of organisms ranging from mold to mushrooms, thriving in environments like soil, compost, and water. They play an essential role in ecosystems but can also wreak havoc on human health. Fungal infections are estimated to kill 2.5 million people annually — a number likely underreported due to limited data.Yet our understanding of fungi, particularly how these highly adaptable organisms will respond to a warming climate, remains limited.A team of scientists from the University of Manchester used computer simulations and climate forecasts to map the future spread of Aspergillus— a common group of fungi found worldwide that can cause aspergillosis, a life-threatening disease that primarily affects the lungs.They found that certain *Aspergillus* species are likely to expand their range as the climate crisis deepens, moving into new areas of North America, Europe, China, and Russia. The study, published this month, is currently under peer review.“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 gained renewed attention thanks to HBO’s popular drama *The Last of Us*, which imagines a world overrun by a mutant fungal infection. While fictional, van Rijn hopes the show raises awareness about the very real and rising threat of fungal diseases.*Aspergillus* fungi grow as small filaments in soil across the globe. Like most fungi, they release vast numbers of microscopic spores that spread through the air. Humans inhale these spores daily, but most people’s immune systems are able to clear them without issue.For people with underlying lung conditions — including asthma, cystic fibrosis, or chronic obstructive pulmonary disease (COPD) — and for those with weakened immune systems, such as cancer patients, organ transplant recipients, or those recovering from severe flu or Covid-19, the threat is far greater.If the body fails to eliminate the spores, the fungus can begin to grow and destroy tissue. “It starts to grow and basically kind of eat you from the inside out, saying it really bluntly,” van Rijn said.Aspergillosis carries high mortality rates — around 20% to 40%, van Rijn noted. It’s also notoriously difficult to diagnose, as symptoms such as fever and cough often mimic more common illnesses, and many doctors don’t initially suspect fungal infection.Fungal pathogens are also becoming more resistant to treatment. There are only four classes of antifungal drugs available, and resistance is rising.That’s alarming as the climate crisis opens up new areas for fungi to colonize. *Aspergillus flavus*, a species that thrives in hot, tropical climates, could expand its range by 16% if fossil fuel emissions remain high. It’s predicted to move into parts of North America, northern China, and Russia. Not only is *A. flavus* resistant to many antifungals, but it can also infect food crops — threatening both public health and food security. In 2022, the World Health Organization added *Aspergillus flavus* to its critical group of fungal pathogens due to its health impact and resistance risks.Meanwhile, *Aspergillus fumigatus*, which prefers temperate climates, is predicted to spread northward toward the Arctic. Its range could grow by 77.5% by 2100, potentially exposing up to 9 million people in Europe.Paradoxically, some regions — including parts of sub-Saharan Africa — could become too hot for *Aspergillus* to survive. But this isn’t necessarily good news. Fungi are vital to ecosystems, including maintaining soil health.A warming world may also be increasing fungi’s temperature tolerance, enabling more species to survive and thrive inside the human body. Extreme weather events — droughts, floods, and heatwaves — can also help disperse fungal spores over vast distances. After the 2011 tornado in Joplin, Missouri, for example, there was a spike in fungal infections.The new *Aspergillus* study “rightfully highlights the threat posed by naturally occurring fungi and the world’s lack of preparedness for changes in their spread,” said Elaine Bignell, co-director of the MRC Centre for Medical Mycology at the University of Exeter, who was not involved in the research.However, many uncertainties remain. “There’s still a huge amount of research to be done,” Bignell told CNN.Despite the deadly nature of aspergillosis, there’s a lack of data on where the fungus lives in the environment and who’s being infected, said Justin Remais, a professor of environmental health sciences at UC Berkeley. He is leading a study of more than 100 million patient records across the U.S., which identified over 20,000 aspergillosis cases between 2013 and 2023. The number of cases is increasing by about 5% annually, he said.“Fungal pathogens are becoming increasingly common and resistant to treatment, and we are only beginning to understand how climate change is contributing,” Remais noted.People are used to hearing about diseases caused by bacteria, viruses, and parasites—but far less about those caused by fungi. “There is a desperate need to reverse this trend given the lethality,” Bignell said."Any of us could be affected in the future."