An appeal from Mucormycosis: Do not call me Black Fungus

The pandemic has educated us with a bunch of new terminologies with the addition of black fungus to the new terror list. First of all, these demons have always resided in microbiology textbooks and acted like a terror for Microbiology students like us. So, they are nothing new. There are Zillions of viruses, bacteria, fungi, and parasites around to nail us to death. They were always there in textbooks, research papers, and clinical notes, it’s just that the pandemic has brought them to newspapers and TV channels. Thanks to mother nature and our immune system we are still alive even with a co-existence with them. Once the immune mechanism is compromised we become prey to those microscopic demons.

*We are not the same*

However, the preface is just to clear confusion about the overlap of two terminologies in news these days. The terms Black fungus disease and mucormycosis are being used interchangeably in popular articles and media. *Unfortunately, these two are entirely different disease that shares some similarities in the pathophysiology and presentation.* The prominent point that misguided us is their ability to attack immunocompromised patients at more or less similar target organs as in the case of COVID-19 infection. Moreover, no scientific literature has mentioned the term “ Black fungus” while describing research on mucormycosis and vice versa. Let us have a quick look at some dissimilarities of these two diseases:

*Different etiological agents*

Blank fungi or sometimes known as black yeasts fall into the class of Dematiaceous fungi that are responsible for a wide variety of infectious syndromes. They are often found in soil and rotten plant materials and are generally inhaled by most if not all individuals. However, its pathogenicity becomes significant in immunocompromised individuals.

The clinical nomenclatures caused by these black fungi are mycetoma, chromoblastomycosis, phaeohyphomycosis, and NOT mucormycosis which is of entirely different origin. The causative genera for these clinical manifestations are Exophiala dermatitidis, Cladophialophora-, Fonsecaea- and Ramichloridium-like strains, known in humans as agents of chromoblastomycosis.

On the other hand, the causative agents for mucormycosis are certain fungi, especially Rhizopus and mucormycetes, which are common contaminants of laboratory cultures. Some of the fungi that are responsible for mucormycosis are Rhizopus species, Mucor species, Rhizomucor species, Syncephalastrum species, Cunninghamella bertholletiae, Apophysomyces species, and Lichtheimia (formerly Absidia) species.

*What is BLACK in it*

At this point, this is clear that the causative agents are completely different for these two types of diseases.  Let us take a break from finding the differences between these two clinical manifestations and concentrate on a more interesting question.

*Why these Dematiaceous fungi are called “BLACK” fungus?*

Interestingly, these fungi possess unique pathogenic mechanisms attributed to the presence of melanin in their cell walls, which imparts the characteristic dark color to their spores and hyphae. On contrary, no such characteristic features are consistently prominent in the microscopic observation of all fungal species that are mucormycosis-causing organisms. Of note, Mucormycosis causes tissue blackening by devitalizing its blood supply, and this black appearance has been misinterpreted, misreported, and misdiagnosed as a black fungus by the media.

*We are on the right path*

Fortunately, despite the confusing terminology, our able physicians have detected the correct disease in COVID-affected individuals- it is Mucormycosis NOT anything caused by black fungus. Therefore, they are predominantly treated by IV amphotericin B and some azoles. Of note, itraconazole and voriconazole demonstrate the most consistent in vitro activity against black fungi (except S. prolificans, which are resistant to azoles) whereas voriconazole is completely ineffective in mucormycosis. Whereas, fluconazole and echinocandins exhibit limited or no activity against both types of diseases.

There are many other similarities in the pathogenesis and presentation that lead to the overlap of the terminologies. Sources for both the etiological agents are the same: soil, composts, rotten woods, and decaying organic matter. Mucormycosis has rhinocerebral, ocular, pulmonary, and gastrointestinal involvements. The blank fungus affects similar organs with less severity than mucormycosis. Mucormycosis is a more morbid condition than diseases involving black fungus. It often requires multiple surgeries even involving enucleation (Complete removal of the eye).

*Final Words*

I am not discussing the co-morbidities that trigger the mucormycosis infection as it is now a well-known topic. Just to mention that there is no scientific evidence that oxygen pipes, oxygen flowmeter, or humidifier are responsible for its spread or origin. Unlike Covid-19, it is not contagious and does not spread from one person to another. Finally, the causative agents are co-existing with us in nature and it is not going to be fatal to you unless you are being treated with high steroids and your diabetes is not under control during your COVID infections days.

References

Baker, R. D. (1957). Mucormycosis—a new disease?. Journal of the American Medical Association, 163(10), 805-808.

Baker R.D. (1971) Mucormycosis. In: The Pathologic Anatomy of Mycoses. Handbuch der Speziellen Pathologischen Anatomie und Histologie (Atmungswege und Lungen), vol 3 / 5. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-80570-7_22

Hoog, G. S. de, Queiroz-Telles, F., Haase, G., Fernandez-Zeppenfeldt, G., Angelis, D. A., H. G. Gerrits van den Ende, A., … Yegres, F. (2000). Black fungi: clinical and pathogenic approaches. Medical Mycology, 38(s1), 243–250. doi:10.1080/mmy.38.s1.243.250

McGinnis MR, Hilger AE. Infections Caused by Black Fungi. Arch Dermatol. 1987;123(10):1300–1302. doi:10.1001/archderm.1987.01660340062020

https://www.cdc.gov/fungal/diseases/mucormycosis/treatment.html

Revankar SG. Dematiaceous fungi. Mycoses. 2007 Mar;50(2):91-101. doi: 10.1111/j.1439-0507.2006.01331.x. PMID: 17305771.