Silver leaf disease is a curse for a variety of botanicals, from pears to roses to rhododendron. Infecting their leaves and branches, the fungus Chondrostereum purpureum can be fatal for the plant if not quickly treated.
Aside from the risk of losing the occasional rose bush, the fungal disease has never been considered a problem for humans. Until this year.
In what researchers suggest is the first reported case of its kind, a 61-year-old Indian mycologist appears to have contracted a rather serious case of silver leaf disease in his own throat, providing a rare example of a pathogen seemingly making an enormous leap across entire kingdoms in the tree of life.
A case study published in June 2023 describes a male patient in India's eastern region presenting to a medical center with a cough and hoarse voice, fatigue, and difficulty swallowing. A CT X-ray scan of his neck revealed a pus-filled abscess next to his trachea.
Lab tests failed to find any bacteria of concern, but a special staining technique for fungi revealed the presence of long, root-like filaments called hyphae.
Fungal diseases aren't exactly uncommon in humans, though of the millions of known species, only a few hundred are capable of causing us much harm. Ringworm, athlete's foot, and thrush commonly make themselves at home in damp areas of our skin, much to our irritation.
Sometimes, especially in people with compromised immune systems, fungi that commonly feed on rotting vegetation, such as species of Aspergillus, can infect deeper parts of our body.
This particular infection didn't look much like any of those, however, prompting the medical specialists to seek advice from a World Health Organization fungi reference and research center, who identified the unlikely suspect from its DNA.
Though a mycologist himself, the patient couldn't recall having worked with this particular species recently. His field work had brought him into contact with decaying material and other plant fungi, potentially explaining the source of his infection.
For pathogens of any variety to nestle inside a host and start replicating, they need the right tools. Not only do they need a means of securing the right nutrients, they need a few tricks to cope with what is essentially a hostile environment bent on tearing them apart with all kinds of chemical weapons and killer agents.
That makes it extremely rare for a fungus adapted to threading its hyphae through leaves and stems to find success in doing the same inside our flesh.
The fact the patient in this case study appeared to have a fully functioning immune system, with no indication of being on immunosuppressant drugs, or having HIV, diabetes, or any kind of chronic illness, makes it even more perplexing. If not a touch concerning.
"Cross-kingdom human pathogens, and their potential plant reservoirs, have important implications for the emergence of infectious diseases," the authors of the study wrote in their report.
Though extremely rare, the fact it clearly could happen makes it an area that deserves attention. Fungi especially pose a significant risk – similarities in fungal and animal biochemistry make the design of suitable vaccines and therapies that can prevent or manage infection a real challenge.
Fortunately in this case, regular drainage of the ulcer with two months on a common antifungal agent did the trick. After two years of check-ups, the patient was still fine with no signs of a repeat infection.
It's unlikely we'll ever know why such a chance infection took root in the first place, and it remains unknown if we'll see its like again.
This research was published in Medical Mycology Case Reports.
A version of this article was first published in April 2023.