While viruses and bacteria frequently capture public attention, pathogenic fungi represent an escalating threat to human and ecological health. These organisms are responsible for devastating diseases affecting plants, animals, and people. Although only about 300 fungal species are known to be pathogenic to humans, serious fungal infections kill an estimated 1.6 to two million people annually.
Fungi That Target Animals and Insects
Among the most dramatic fungal pathogens are those that infect insects, with Ophiocordyceps unilateralis, or “zombie-ant fungus,” being a prime example. This fungus has a specific life cycle that begins when a spore penetrates the exoskeleton of a carpenter ant. Once inside, the fungus proliferates and releases compounds that manipulate the ant’s behavior, compelling it to climb a plant and clamp its mandibles onto a leaf in a location with ideal humidity for the fungus to grow.
After the ant dies, the fungus consumes its tissues and sprouts a stalk from the ant’s head, which releases new spores onto the forest floor. This behavioral manipulation is a sophisticated survival strategy that ensures the fungus’s reproductive success.
While Cordyceps is well-known, other fungi have caused ecological disasters. The chytrid fungus, Batrachochytrium dendrobatidis (Bd), has driven global amphibian declines, contributing to the extinction of numerous species. This pathogen infects the skin of frogs, toads, and salamanders, disrupting their ability to absorb water and electrolytes, which leads to death. The spread of Bd has been documented on every continent where amphibians live, representing the greatest recorded loss of biodiversity from a single disease.
Fungi That Threaten Humans
The threat of pathogenic fungi extends into human clinical settings, where most serious infections are opportunistic. These primarily affect immunocompromised individuals, such as patients with advanced HIV/AIDS, those undergoing chemotherapy for cancer, or organ transplant recipients taking immunosuppressive drugs. In these vulnerable populations, fungi that are normally harmless can become life-threatening invaders.
A prominent example threatening healthcare facilities is Candida auris. First identified in 2009, this yeast has spread globally, causing severe infections with mortality rates ranging from 30% to 72% in hospitalized patients. C. auris is dangerous due to its frequent resistance to multiple antifungal drugs, making infections difficult to treat. It is also difficult to eradicate from hospital environments, as it persists on surfaces and spreads between patients.
Aspergillus fumigatus, a common mold, can cause a lung infection called invasive aspergillosis in immunocompromised individuals, with mortality rates as high as 88%. Similarly, Cryptococcus neoformans is an environmental fungus that can cause a severe form of meningitis, particularly in people with HIV/AIDS.
The Rise of Antifungal Resistance
The rise of antifungal resistance is a challenge in combating fungal infections. Similar to antibiotic resistance, this occurs when a fungus evolves to survive the drugs designed to kill it. This can happen through genetic mutations that alter the drug’s target or changes that allow the fungus to pump the drug out of its cells. As a result, treatments become less effective, leading to prolonged illness and higher mortality.
A driver of resistance is the extensive use of fungicides in agriculture. Many antifungal compounds used to protect crops are chemically similar to medications used in human medicine. When these fungicides are used widely, they create selective pressure that encourages the evolution of resistant fungal strains. These resistant fungi can then infect humans, making them difficult to treat because standard medical treatments may be ineffective.
Could a Fungal Pandemic Happen?
The idea of a fungal pandemic that turns people into zombies like Cordyceps does to ants is scientifically improbable. A primary human defense against most fungi is our high core body temperature of around 98.6°F (37°C). Most fungal species cannot thrive in such warm conditions, making mammals less susceptible to fungal diseases than insects or amphibians.
Furthermore, the human immune system is far more complex than that of an insect, possessing multiple layers of defense designed to eliminate pathogens like fungi. For a fungus like Cordyceps to control a human, it would need to overcome these formidable thermal and immunological barriers. Most serious fungal pathogens are also not easily transmissible from person to person, which is another factor that makes a widespread pandemic improbable.
Climate change presents a new variable, as rising global temperatures could force fungi to adapt to warmer conditions. Scientists theorize this adaptation could allow some fungi to breach the human thermal barrier, leading to new pathogens capable of causing disease in humans. While a zombie apocalypse remains fiction, the threat of fungi adapting to a warmer world is a growing public health concern.