Tom Volk's Fungus of the Month for February 2003

This month's fungus is Sporothrix schenckii, cause of Rose-picker's Disease

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Sporothrix schenckii and rose

When drinking wine amongst the roses
Or guzzling beer while throwing bricks
Or playing games in bales of hay
Where lurks the tricky sporothrix,
Beware, the price you pay for play
When you get struck by dread mycoses

---author unknown

In this month of Valentine's Day and love and flowers and all that, what could be a better choice than a fungus that grows on roses? More specifically Sporothrix schenckii grows on the thorns of roses and can be inoculated into the body by an innocent prick of the thorn. The fungus can then morph to a yeast and grow in the lymph system, manifesting itself as lesions in the lymph nodes, as shown below and to the right. You can actually trace the location of this person's lymph nodes in his arm. The fungus in this case was acquired with the puncture of a rose thorn.

Sporotrichosis showing up at each lymph node

We generally characterize mycoses by which part of the body they colonize. Most patients are not even aware of their superficial mycoses, which only grow on dead skin, hair and nails, because they never secrete their metabolites into the body. The cutaneous mycoses infect skin, hair, and nails and secrete their metabolites into the skin, so that the person is definitely aware of the infection. An example of this is Epidermophyton floccosum, one of the causes of athlete's foot. In subcutaneous mycoses, the fungus must be traumatically implanted into the body. The deep (aka systemic) mycoses are inhaled into the lungs and subsequently are transported to other internal organs, usually through the bloodstream.

Most commonly, sporotrichosis is a chronic infection characterized by nodular lesions of subcutaneous tissue and adjacent lymphatics that suppurate (make pus), ulcerate (digest the tissue) and drain. There are several kinds of diseases that may be caused by Sporothrix

Bear fashioned from Sphagnum mossIn nature Sporothrix lives as a saprophyte on wood, decaying vegetation (including rose thorns), Sphagnum moss, animal excreta and soil. Sporothrix can also cause lung infections, and is particularly abundant in central Wisconsin and other areas where Sphagnum moss is abundant. Sporothrix can naturally grow on Sphagnum moss, but it is only rarely transmitted to humans in the field. However, when this moss is collected and used for floral arrangements, this provides the right conditions for Sporothrix to thrive. Workers who are exposed to large quantities of the Sphagnum are likely to inhale large quantities of Sporothrix spores. To the left is a little sphagnum bear sent to me by some of the moss collectors in central Wisconsin.

Although Sporotrichosis is the only common subcutaneous mycosis the temperate zone, the tropics and subtropics host a variety of other subcutaneous mycoses, such as Chromoblastomycosis, Mycetoma, Pseudallescheriasis, and Phaeohyphomycosis. None of the fungi that cause these diseases can infect the subcutaneous regions on their own-- they need some sort of trauma to the body, such as a wound or puncture, that inoculates the spores of the fungus into the lower regions of the skin.

yeast, asteroid body, cigar bodies in Histopathology of sporotrichosisDiagnosis of sporotrichosis must be confirmed (i.e. distinguished from the other subcutaneous mycoses) by looking at sections of infected tissue. Budding yeasts can often be seen in histopathological sections of the lesions. However, depending on the conditions and the strain of fungus, sometimes these sections contain cigar bodies or asteroid bodies instead of (or in addition to) the yeasts. There seems to be quite a bit of variability even within a single patient. The other subcutaneous mycoses have their own distinctive histopathologies.

Diagnosis of the disease can sometimes be aided by the sporotrichin skin test. Patients with all forms of the disease develop circulating antibodies. Although it is not clear whether these are of any protective value, they do allow for serological confirmation of the disease. There is a skin test available, similar to the skin prick tuberculosis (TB) test. However, although such tests are usually positive in cases of pulmonary infection, they are mostly negative in cases of skin infection. People living in high endemic areas develop a hypersensitivity response to a skin test. Upon subsequent exposures to the fungus, this hypersensitivity appears to either prevent the disease or at least modify it to a less severe form. The skin test may also be useful in determining prevalence of the organism in an area; in regions where no cases have been reported, almost all people test negative.

The disease responds well to treatment with a saturated solution of oral potassium iodide. Although it works against cutaneous infection the mode of action unknown. Direct application of heat may kill the fungus in early infection, especially in more distal lesions. Ketoconazole may have some effect in cutaneous infection. Itraconazole shows some promise at low doses for several months. Intravenous Amphotericin B, usually the drug of last resort for fungal infections, works poorly and slowly

upper pic--Sporothrix colony, morphing from fuzzy mycelium to slimy yeast.  lower pic colonies grown at the indicated temperatureSporothrix schenckii is one of five species of thermal dimorphic fungi of medical interest. (Can you name the others by looking at my Fungus of the Month web pages?) Dimorphic fungi produce hyphae in vitro (literally "in glass") at temperatures below 37ºC, but produce a yeast form in vivo (literally "in living things") and in vitro at 37ºC and above. Many studies have been made of the morphological and physiological changes and changes in cellular composition that accompany the dimorphism. Newly isolated cultures produce moist yeast like colonies with a flat or finely wrinkled surfaces. White to creamy, but becomes dark brown or black. Pigmentation is extremely variable. Two kinds of conidia: hyaline and thin-walled or dark brown and thick-walled (triangular). Sometimes in culture for a long time the fungus loses its pigmentation. The colony shown to the right is in the process of morphing from the hyphal to the yeast form. Note the fuzzy mycelium and the slimy yeast.

Yeast formation at 37ºC is an extension of the blastoconidiation process. Acropetalous budding (i.e. from the top) of conidia borne on mycelia was thought to be the source of the yeast, but it was shown that yeast cells bud directly from the sides of the mycelium.

Sporothrix schenckii may be closely related to Ophiostoma minus, a perithecial member of the Ascomycota related to the organisms causing Dutch elm disease, Ophiostoma ulmi and O. novo-ulmi. (see Berbee, M.L. and J.W. Taylor. 1992. 18s ribosomal RNA gene sequence characters place the human pathogen Sporothrix schenckii in the genus Ophiostoma. Experimental Mycology 16: 87-91). Like Ophiostoma, in nature Sporothrix lives as a saprophyte on wood, decaying vegetation, animal excreta and soil. However, no one has been able to observe the conversion to the Ophiostoma teleomorph directly, so Sporothrix schenckii must remain classified in the deuteromycetes. In terms of its pathogenicity, I guess it doesn't really matter what we call it. As Shakespeare might have written (to be said aloud, using your best British accent),

"What's in a name? That which we call Sporothrix
by any other word would still cause subcutaneous mycosis."

 ---from Romeo and Sporothrix - (1595) Act II. - Scene 2. - Rows: 47-48 

I hope you learned something about Sporothrix today. All of the pictures on this page are from my good friend Dr. John Rippon, who has given me almost all of his medical mycology slides. Thanks John!

I hope you have a Happy Valentine's Day. But watch out for those roses... and the motive of the person who gave them to you! 

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