Test your diagnostic skills!
Fifteen years ago someone described a single strain of a new yeast from a human ear (Satoh et al. 2009). This fungus seemed totally insignificant and was soon forgotten. But today we know the species as Candida auris*, a “deadly fungus spreading at an alarming rate”, according to NBC News. This teaches us that even unknown and occasional fungi that you may encounter in clinical samples can turn out to become major pathogens. Epidemic situations can change dramatically within a decade. Sporothrix brasiliensis, not known before 1990 (Barros et al. 2004), is a similar example of a truly emerging fungus and the dermatophyte Trichophyton indotineae is the latest newcomer (Gupta et al. 2024).
A first impression of the potential significance of fungi in clinical samples can be taken from the frequency in their natural habitat. Ubiquitous saprobes such as Cladosporium species are abundantly present all around us, and an occasional traumatic or inhalative infection can then not be excluded (Duquia et al. 2010). Even our fungal best friend, Saccharomyces cerevisiae, has been described from gastrointestinal or fungemic cases (Popiel et al. 2015 and see numerous cases in de Hoog et al. 2020). But what to think of rare and bizarre fungi such as Myocopron laterale or Mycotypha microspora that were recently added to the Atlas of Clinical Fungi? As several other mucoralean fungi, Mycotypha species rapidly colonize and degrade soft substrates. Gastrointestinal infections have been reported (Trachuk et al. 2018), and given the often destructive character of related Mucorales in susceptible patients, this fungus should be taken seriously. Muyocopron has been surrounded by nomenclatural confusion, and may therefore be overlooked. The genus contains a small number of endophytic fungi, living asymptomatically inside living plants (Hernandez-Restrepo et al. 2019), but human traumatic from plant origin (Padhye et al. 1995), in immunocompromised patients (Yang et al. 2023) and also canine and feline infections (Crespo-Szabo et al. 2021) have been described.
Name changes have also concealed the numerous traumatic skin and eye infections caused originating from plant material by fungi that were taken together in the past as ‘coelomycetes’. Today we can sequence them and find generic names that are located in the phylogeny of the fungal Kingdom. See for example under Didymella and Diaporthe in the Atlas: in culture they are characterized by pycnidial fruitbodies with asexual conidia. Fungi under these names seem to be newly emerging, but they have been described frequently from human infections under names that we now consider as obsolete.
Another name problem concerns the dermatophyte genus Nannizzia. Nannizzia gypsea (previously classified in Microsporum) is mostly classified as a soil fungus, but see the Atlas for the numerous cutaneous infections that have been described. Remarkably, even a specific infection type, known as ‘crural white dot’ seems to prevalently caused by this fungus (Prochnau et al. 2005; Yin et al. 2019).
The Atlas follows the literature on all clinical fungi. Full descriptions and extended information is given as soon as a proven case report appears. Agents of less clear significance can be found in the back of the book in the chapter ‘Doubtful …’, together with all the obsolete names. Quite likely, some of the recent additions to this list will be treated as important pathogens in the future.
The next Atlas-based courses where this diversity is explained will be held 23-28 September 2024 in Rochester, U.S.A., May 2025 in Recife, Brazil, October 2025 in Jinin, China, and January 2026 in Nijmegen, The Netherlands.
*A recent paper (Liu et al. 2024) proposed a name change to Candidozyma auris.