A man in India is the first human known to be infected by a fungus called Chondrostereum purpureum, a pathogen that is most well-known for causing a disease called silver leaf in plants, reports a new study.
The patient, who was 61 at the time of the diagnosis, made a full recovery and has not experienced any recurrence of the infection after two years of follow-up observations. However, this “first of its kind” case study exemplifies the risks that fungal pathogens pose for humans, especially now that climate change and other human activities like rampant urbanization, have opened a “Pandora’s Box for newer fungal diseases” by contributing to their spread, according to the study.
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Fungal pathogens are having a pop culture moment because they are the source of a fictional disease depicted in apocalyptic game The Last of Us, which was recently adapted into the acclaimed HBO series of the same name. But these microbes are also a real-life scourge that infect about 150 million people every year, resulting in about 1.7 million deaths.
Though millions of fungal species exist, only a very small fraction of them are able to infect animals, including humans, because our bodies present challenges to these invaders such as high temperatures and sophisticated immune systems.
Soma Dutta and Ujjwayini Ray, doctors at Apollo Multispecialty Hospitals in Kolkata, India, have now added one more fungus to that small list of human invaders with their unprecedented report of a C. purpureum infection. The patient, a plant mycologist, had suffered from cough, fatigue, anorexia, and a throat abscess for months before his hospital visit, and was probably exposed to the fungus as a result of his profession.
When conventional techniques failed to diagnose the disease, the pathogen was sent to a World Health Organization center based in India where it was finally identified using DNA sequencing. The case “highlights the potential of environmental plant fungi to cause disease in humans and stresses the importance of molecular techniques to identify the causative fungal species,” according to their recent study in the journal Medical Mycology Case Reports.
“There are so many fungus that are causing human infection, but any plant fungus causing human infection is very rare,” Dutta told Motherboard in an email.
“Prolonged exposure and genetic susceptibility could be the possible reason for infection in this particular patient,” she added. “I think genetic susceptibility for any infection should be explored.”
C. purpureum can infect a variety of different plants with silver leaf disease, an often fatal condition that is named after the color that the pathogen induces on the leaves on the hosts. It is the latest in a growing number of fungal pathogens that have infected humans, which are buoyed on in part by human activities, such as urbanization, travel, and commerce.
“This is a first of its kind of a case wherein this plant fungus caused disease in a human,” Dutta and Ray said in the study. “This case report demonstrates the crossover of plant pathogens into humans when working in close contact with plant fungi. The cross-kingdom pathogenicity demands much work to be done in order to explore insights of the mechanisms involved, thus leading to possible recommendations to control and contain these infections.”
Human-driven climate change is also accelerating the spread of infectious diseases, including fungal pathogens, by allowing microbes to adapt to higher temperatures (like those in mammal bodies), expand their range, and interact with new hosts in the aftermath of extreme weather events.
“Global warming increases the adaptability of infection to the human body,” Dutta told Motherboard. “It is hypothesized that thermostability of any infection may increase due to global warming and the infection may be able to thrive and multiply in the human body.”
And though fungal diseases have maintained a lower profile in epidemiology compared to other pathogens, they may be more dangerous than viruses or bacteria in some contexts.
“While viral and bacterial diseases receive most attention as the potential cause of plagues and pandemics, fungi can arguably pose equal or even greater threats,” according to a 2021 study in PLoS Pathogens. “There are no vaccines available yet for fungal pathogens, the arsenal of antifungal agents is extremely limited, and fungi can live saprotrophically, producing large quantities of infectious spores and do not require host-to-host contact to establish infection. Indeed, fungi seem to be uniquely capable of causing complete host extinction.”
In addition to avoiding the spread of new fungal pathogens that can directly infect humans, researchers also point to the damage these diseases can deal to crops and ecosystems that people depend on. For this reason, Dutta and Ray recommend more research into the nature of these infections and strategies to mitigate their spread.
“Cross-kingdom human pathogens, and their potential plant reservoirs, have important implications for the emergence of infectious diseases,” Dutta and Ray said. “Fungi are also responsible for various infections in plants that cause destruction of millions of plants and crops” and “produce toxins that contaminate food and cause acute toxicity.”
“Over the past several decades multiple new pathogenic fungi have emerged,” they concluded. “A notable emergence of the multidrug resistant fungus Candida auris has spread all over the world and has become a significant threat. The worsening of global warming and other civilization activities opens Pandora’s Box for newer fungal diseases.”
Update: This article has been updated to include comments from study author Soma Dutta.
