Tom Volk's Fungus of the Month for February 1998

This month's fungus is Epidermophyton floccosum, one of the causes of athlete's foot.

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Epidermophyton floccosum macroconidia I can see the emails now---"Well, this is quite a change of pace from the usual fungus of the month." I'm teaching Medical Mycology this semester, and my new scanner is working, so I get to have some interesting new images online. Epidermophyton floccosum, the microscopic fungus to the left causes a malady known as athlete's foot (tinea pedis). Many other closely related fungi,technically known as dermatophytes, in the genera Trichophyton and Microsporum also cause athlete's foot, along with other human diseases such as "ugly toenail fungus" (technically known as tinea unguinum or onychomycosis), ringworm (tinea corporis and tinea capitis) and "jock itch" (tinea cruris). The "tinea" part of those disease names comes from the 19th century when these diseases were thought to be caused by worms (tinea) rather than fungi. When people started looking at them in the microscope it was clear that they were not worms, but the name still stuck. (Remember, there's lots of other things that have names that make no sense-- like "Grape Nuts"-- no grapes, no nuts.....)
tinea pedisTo the right is a severe case of tinea pedis, athlete's foot caused by Epidermophyton floccosum. This picture, like all the pictures on this page are from Dr. John Rippon, Professor Emeritus at the University of Chicago. When John retired and I got my present job at the UW-La Crosse to teach Mycology and Medical Mycology, he gave me most of his slide collection. I am extremely grateful for this, and I will eventually, with his permission make this collection available on CD-ROM. However that's a long way off-- these are the only slides of his I've scanned in so far. Thanks John!
There are some commercial products and drugs available that treat dermatophyte infections relatively well. However most fungal infections take a long time to cure. Fungal infections are very difficult to treat without causing toxic effects in the person with the disease. In contrast, bacterial infections are relatively easy to treat because humans are eukaryotes and bacteria are prokaryotes, and there are a wide variety of drugs and antibiotics available in most cases. On the other hand fungal infections are very difficult to treat because both animals and fungi are eukaryotes, sharing many of the same chemical and cell structural characteristics. It's very difficult to kill the fungus without killing the person, so very low doses of the drug must be used over a long period of time. Please don't email me asking how to get rid of your fungal infection; I'm not a medical mycologist or a medical doctor-- I just play one on the internet.
ecothrixThe image to the right shows an infection of the hair caused by a fungus. These are what are referred to as superficial infections, infecting the hair and the outer dead layer of the skin. The dermatophytes cause cutaneous infection on the outer layer of the living part of the skin. They live primarily on keratinized tissue. Many other fungi cause subcutaneous infections in the lower areas of the skin-- these must be traumatically implanted with an injury. The worst kind of fungal infections are the systemic mycoses, such as histoplasmosis, blastomycosis, coccidioidomycosis, and paracoccidioidomycosis (as well as a number caused by opportunistic fungal pathogens). These usually begin as a lung infections that can spread to other internal organs. These are extremely difficult to treat.
For more information on medical mycology I suggest you visit the Medical Mycology Page at the Medical Mycology Research Center at the University of Texas Medical Branch at Galveston. This site is very well put together and contains lots of information on and pictures of various human diseases and conditions that are caused by fungi.
I hope you enjoyed learning something about medical mycology. It's really an interesting field. Many fungi that were considered to be innocuous soil inhabiters are now becoming problems in immunosuppressed people, such as those on high doses of certain steroids and other medications, or people with AIDS. Medical Mycologists worldwide are working to find new drugs to cure these infections.
By the way I'm still looking for my own copy of John Rippon's Medical Mycology textbook, 1988. 3rd edition. (not the 2nd edition!). If you've got one to sell please email me!

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