Fungi spread as climate warms

Rising global temperatures, driven by climate change, are expanding the reach of deadly fungal pathogens, particularly those in the Aspergillus family. New research highlights how these fungi, which already infect millions annually, could spread to new regions, including northern Europe, Asia, and the Americas. This article explores the growing threat of Aspergillus species, the factors driving their proliferation, and the public health and ecological implications of their spread.

The Growing Threat of Fungal Pathogens

Fungal pathogens are increasingly recognized as a global health threat, with Aspergillus species among the most dangerous. These fungi are responsible for an estimated 3.8 million deaths annually, with 2.5 million directly attributable to invasive fungal infections. Aspergillosis, a lung disease caused by inhaling Aspergillus spores, is a leading concern due to its ability to spread to other organs, including the brain.

• Aspergillus fumigatus: Identified by the World Health Organization (WHO) in 2022 as one of four critical fungal pathogens, A. fumigatus thrives in high-temperature environments like compost heaps, equipping it to survive in the human body at 37°C. Research funded by the Wellcome Trust projects that by 2100, under a high fossil fuel emissions scenario, A. fumigatus could expand its range by 77%, exposing an additional 9 million people in Europe to infection risk.

• Aspergillus flavus: This species, which lives on crops, could expand into 16% more territory by 2100, gaining footholds in northern China, Russia, Scandinavia, and Alaska. A. flavus produces aflatoxins, harmful chemicals linked to liver damage and cancer, which pose threats to both human health and food security.

Why Fungi Are a Unique Peril

Fungi present unique challenges compared to other pathogens like viruses or bacteria:

• Hard-to-Detect Spores: Aspergillus spores are ubiquitous and difficult to detect, often leading to late or missed diagnoses. Symptoms are frequently mistaken for other conditions, complicating treatment.

• Limited Treatments: There is a shortage of effective antifungal drugs, and existing treatments face growing resistance. The development of new antifungals is hindered by high costs and low profitability.

• Mycological Mysteries: Over 90% of fungal species remain unknown to science, according to a 2023 Royal Botanic Gardens, Kew report. This knowledge gap limits our ability to predict and combat fungal threats.

Climate Change as a Catalyst

Climate change is reshaping the geographical distribution of fungal pathogens by creating warmer, more favorable conditions for their growth:

• Temperature Tolerance: Species like A. fumigatus grow rapidly at high temperatures, giving them a “fitness advantage” to colonize human lungs, as noted by Professor Elaine Bignell from the MRC Centre for Medical Mycology.

• Extreme Weather Events: Droughts followed by heavy rains can disturb soil, releasing fungal spores into the air. Wildfires, another climate-related phenomenon, may further amplify spore dispersal.

• Shifting Habitats: As temperatures rise, Aspergillus species are moving northward, while some existing habitats in regions like Africa and Brazil may become inhospitable, disrupting ecosystems where fungi play vital roles in chemical recycling.

Health and Societal Impacts

The spread of Aspergillus poses significant risks, particularly to vulnerable populations:

• High-Risk Groups: People with weakened immune systems—due to conditions like asthma, cystic fibrosis, or treatments like chemotherapy—are especially susceptible. While most individuals inhale Aspergillus spores without issue, infections in these groups can have high mortality rates.

• Disproportionate Burden: Data from the University of California, Berkeley, indicates that since 2020, aspergillosis cases have risen sharply among Latino individuals and rural populations in the U.S. This may be linked to severe COVID-19 cases, limited healthcare access, and environmental exposures like pollution.

• Food Security Threats: A. flavus produces aflatoxins that contaminate crops, exacerbated by higher temperatures and CO₂ levels. This not only threatens human health but also disrupts agricultural systems.

Ecological and Industrial Roles of Aspergillus

While Aspergillus species pose health risks, they also have beneficial roles:

• Industrial Applications: Some species are used in industrial chemistry, soy sauce fermentation, and sake production.

• Ecosystem Functions: Aspergillus contributes to chemical recycling in ecosystems, and its disappearance from certain regions could have cascading ecological effects.

Research and Public Health Responses

Ongoing research is critical to addressing the fungal threat:

• UC Berkeley’s Big Data Project: A five-year study analyzing medical records from 100 million U.S. patients aims to identify factors influencing fungal infection rates. The project has already linked climate-driven changes, like droughts, to the spread of pathogens such as Coccidioides, which causes Valley fever.

• Global Awareness: The WHO’s 2022 fungal priority list and increased research funding, such as from the Wellcome Trust, signal growing recognition of the threat.

• Challenges in Drug development: The lack of financial incentives for antifungal drug development remains a barrier, as highlighted by experts like Professor Darius Armstrong-James.

The Road Ahead

The proliferation of fungal pathogens like Aspergillus underscores the urgent need for action:

• Enhanced Surveillance: Improved diagnostic tools and training for healthcare providers can help detect infections earlier.

• Climate Mitigation: Reducing fossil fuel emissions could slow the spread of fungal habitats, protecting millions from exposure.

• Research Investment: Greater funding for mycology and antifungal drug development is essential to close knowledge gaps and improve treatments.

The global spread of Aspergillus fungi, driven by climate change, represents a stealthy but profound threat to human health, food security, and ecosystems. As Norman van Rhijn warns, the world is nearing a “tipping point” in fungal pathogen proliferation. By prioritizing research, public health measures, and climate action, we can mitigate the risks posed by these ancient and resilient organisms.