Black, yellow, green, and white fungi everywhere! Reading through the Indian lay press on COVID-19–associated invasive fungal infections (CA-IFIs) can be a perplexing exercise these days. Certainly, mycologists use color classifications. As illustrated below, dematiaceous fungi are known for their ability to produce melanoma pigment (and a dark color), and Talaromyces marneffei is known as the red fungus because it produces a red pigment in agar. But the color-coding terminology for various fungi associated with CA-IFIs is confusing and somewhat arbitrary. Yet, because people search on these terms frequently, these terms provide both a challenge and an opportunity for education.
Below is a guide that provides clarity on the origin of the fungus color scheme used in the contemporary Indian press for CA-IFIs as well as the explanation for why the terminology is not helpful. Of note, we’ve also included the toxic mold (black fungus) miscoding as well, since that’s another example of how arbitrary fungal color can lead to confusion.
We wish to thank Sanjay Revankar, MD, Professor of Infectious Diseases at Wayne State University and expert on fungus diagnostics and rare molds, for reviewing this content and helping us break the colloquial miscoding of fungi. We also thank John R. Perfect, MD, Chief of the Division of Infectious Diseases at Duke University School of Medicine, and our steering committee for their contributions.
|Colloquial Name for Fungus||Colloquially Associated Fungal Pathogen||Explanation||Why the Terminology Is Misleading or Confusing|
|Black Fungus or Black Mold||Mucormycosis associated with COVID-19 in India|
Also, in the United States, black “toxic” mold is sometimes used to describe dark fungal growth in warm, damp, indoor environments. Sometimes this is assumed to be Stachybotrys chartarum, which is a toxin-producing mold[CDC 2019]
|The infection is called black fungus because the invasion of tissues causes the skin color to turn black [Black, white and yellow fungus 2021]|
Molds can grow on surfaces and produce a range of colors
|The confusion arises with what is being described; the "black" fungus mentioned in India is the product of the necrosis associated with mucormycosis infections, not the actual color of the fungus. Mucormycosis-associated molds are not black in laboratory cultures but may be gray to dark gray or brown|
Mycology experts tend to think of brown/black fungi as names for dematiaceous fungi, which are molds that produce melanin and cause phaeohyphomycosis, chromoblastomycosis, and mycetoma.[Ogawa 2019; Yew 2014] They do not seem to be associated with COVID-19 infection
Color is not an indication of how dangerous a mold is. Although Stachybotrus chartarum is a toxin-producing mold [Ulrich 2020] that is known as a black toxic mold, there is currently no test for this mold. The most important aspects of addressing a mold issue are remediation, addressing underlying moisture issues, and seeking medical care for any potentially associated symptoms [You can control mold 2020]
|Green Fungus||Aspergillus spp.||Aspergillus spp. can appear green in lab cultures. Also caused by common mold in compost piles/decaying leaves [Aspergillosis 2019]||Aspergillus fumigatus, the most common species, typically appears blue-green in culture, but other Aspergillus spp can be yellow to brown to black as well, depending on the species [Sugui 2014] |
The search for green fungus also brings up green nail syndrome, or chloronychia, an infection of the nails caused by the bacterium Pseudomonas aeruginosa [Lee 2021]
Other species that could be confused with green fungus are Trichoderma spp., which are known as green mold [Colavolpe 2015], and Metarhizium spp., which produce green fluorescent protein [Barelli 2020]
|White Fungus||Candida spp.||Candida grows in the lab as white/creamy white spots on plates of agar. In humans, Candida appears as white, creamy spots on the mucosa [Candidiasis][Hamid 2014] |
Also, Candida albicans is the most commonly isolated species (albicans means white) [Seladi-Schulman 2018]
|Though Candida is a cream-colored yeast in lab culture, many molds are also white in culture when they are not producing spores and cannot be distinguished just by their appearance [Hamid 2014] |
White fungus has also been used to describe variants of mucormycosis [Kingsland 2021]
Tinea versicolor, which comes up when the term “white fungus” is searched, is a fungal infection of the skin that causes light patches on the skin[Karray 2020]
The term has also been associated with Aspergillus flavus [Ghosh 2021]
|Yellow Fungus||General fungal infection characterized by the presence of pus|
Has also been used to describe variants of mucormycosis, aka Mucor septicus [First case of patient infected 2021]
|Pus is commonly associated with bacterial infections, so the term is also used by the lay press for suspected fungal infections |
The infection is called yellow fungus because the “pus formed in the wounded area is yellow” [Black, white and yellow fungal infections 2021]
|The concept of "yellow" fungus is not useful |
Most fungal infections do not produce "pus," as do bacterial infections
Regarding the Mucor septicus case, the case cited had no specific details and the species has no confirmed human case of infection, so one should be skeptical of that. Actually, Mucor septicus is a synonym for Fuligo septica, a slime mold that does not cause infection in humans
Many molds appear yellow in culture, including Aspergillus flavus (flavus means yellow in Latin) and many others produce a yellow pigment
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Centers for Disease Control and Prevention. Facts about Stachybotrys chartarum. Atlanta, GA: Centers for Disease Control and Prevention; 2019. https://www.cdc.gov/mold/stachy.htm. Accessed August 18, 2021.
Centers for Disease Control and Prevention. You can control mold. July 17, 2020. https://www.cdc.gov/mold/control_mold.htm. Accessed August 18, 2021.
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