Tom Volk's Fungus of the Month for November 2002

by Tom Volk and Nik Zitomer

This month's fungus is Stachybotrys chartarum, a mold that allegedly causes "sick building syndrome."

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Stachybotrys chartarum conidiophore and conidia

We can always tell when there's been an exposé on this fungus on one of the over-sensationalized TV news magazines (like 20/20, Dateline, or 60 Minutes) or in major newspapers because our email inboxes fill up the next day with inquiries about this misunderstood black mold. We think people should learn more about this fungus before condemning it as the cause of "sick building syndrome." We will propose to you here that Stachybotrys chartarum has not yet been proven to cause bodily harm to humans or other animals in "sick buildings."

Stachybotrys chartarum ornamented conidiaStachybotrys is a deuteromycete fungus in the family Dematiaceae. The most important species in this genus is Stachybotrys chartarum, formerly known as Stachybotrys atra. This species is important for a variety of reasons, most of which relate to the fact that it can produce a novel class of trichothecenes, a type of mycotoxin. (you might recall that Aflatoxin is another mycotoxin that is produced by Aspergillus species.) This web page presents information about toxicoses caused by Stachybotrys chartarum, the novel toxins it produces, its possible implication in "sick building syndrome," and the role it may have played in an epidemic of infant pulmonary hemorrhage in Cleveland, Ohio in 1994.

Stachybotrys conidia formation-- drawings by Nik ZitomerWe mentioned above that Stachybotrys chartarum is a deuteromycete, a Dematiaceous Hyphomycete. What does that mean? "Deuteromycetes," also known as Fungi Imperfecti,(encompassing the anamorph or mitosporic state) are those fungi for which a sexual state (teleomorph, perfect, or meiosporic state) is unknown. The form-class Hyphomycetes have conidiophores that are not borne in a specialized structure (such as a pycnidium or acervulus). Members of the form-order Hyphomycetales have scattered conidiophores. The form-family Dematiaceae have dark-colored hyphae and spores (compared to the Moniliaceae, which have light colored hyphae and spores). The genus Stachybotrys produces a mass of sticky, single-celled ornamented conidia from phialides on each conidiophore, as shown to the left and right. A related genus, Pithomyces, is nearly identical except for its septate spores. Memnoniella is also similar, but its single celled spores remain in a chain instead of clustering in a sticky mass as in Stachybotrys.

Identification of molds is very difficult and takes a great deal of training, experience, and practice. Unfortunately, the personnel of most "Environmental" or "Indoor Air Quality" companies have very little training in Mycology, let alone in mold identification. There are many (many) incompetent diagnoses being made. There is no regulation of the industry-- anyone can call themselves an environmental mold specialist. Ask for credentials and training before hiring one of these companies to investigate your mold problem. Molds must be identified to species to determine if they can cause a problem.

Stachybotrys on drywall, under dissecting microscope Stachybotrys with drywall fibers, closeupThis fungus grows extremely well on substrates that are high in cellulose, particularly when those substrates are wet. This means that typical building materials, such as wood and drywall, when wet, make a good habitat for Stachybotrys. On the left you can see the dark conidia in contrast to the drywall, and on the right is a magnified view showing the fungus sporulating on the drywall fibers. Stachybotrys is a moderately common inhabitant of moist areas in homes, and its spores can cause some possible health risks. Stachybotrys is commonly isolated in buildings with mechanical or structural defects that lead to areas of increased moisture accumulation. It is important to note, however, that Stachybotrys is usually isolated in fewer numbers than other contaminant fungi such as Aspergillus, Alternaria, Penicillium and Cladosporium. High spore counts of any fungi in a building can be detrimental to health for various reasons, including causing allergic fungal sinusitis, when fungal mycelium may actually grow in the sinus cavities. Thus, Stachybotrys can cause health issues on this basis alone. Stachybotrys poses an additional threat, however, in that it can make several members of a class of mycotoxins called trichothecenes.

macrocyclic trichothecenes produced by Stachybotrys-- drawings by Nik ZitomerTrichothecenes are toxins that are produced by at least five genera of fungi, including Fusarium, Stachybotrys, Tricothecium, Myrothecium, and Cephalosporium. Many of these toxins have a large impact on agriculture, as some of the fungi that can produce them are pathogenic on crop plants. Many epidemics have resulted upon crops being infected with trichothecene- producing fungi. The mode of action of trichothecenes is by functioning as protein synthesis inhibitors. The class of trichothecenes produced by Stachybotrys chartarum is unique in that they include a large ring portion. Three mycotoxins are produced by Stachybotrys-- Roridin E, Verrucarin J, and Satratoxin H. Note the structure of T-2 toxin, a trichothecene produced by Fusarium species, which lacks the large ring. These toxins are present on the spore surface, and thus can be (theoretically) inhaled into the lungs, although scientific evidence for this is, so far, lacking.

It also likely that other factors are involved in cases of sick building syndrome. These could include physical and chemical stresses, and even psychological stresses caused by the work environment. It is possible that Stachybotrys plays a role in this syndrome, but it is unlikely that it is the primary etiologic (causative) agent.

Stachybotryotoxicosis is the disease that results upon ingestion of the toxins produced by Stachybotrys. The disease is most common in horses, where they encounter the fungus and its toxins through feed and/or bedding contaminated with Stachybotrys. The first recognized cases of Stachybotryotoxicoses occurred in Russia between the 1920s and 1930s. The symptoms of this mycotoxicosis are oral lesions, swelling of the lips and lymph nodes, elevated body temperature, weak pulse, and, if allowed to progress, death. Stachybotryotoxicosis has since been reported in several Eastern European countries, as well as in France, India, and South Africa. However, to our knowledge, there are no clinical or experimental studies that have proven a link between INHALATION of the spores and any of these symptoms. Thus, as far as has been proven, you would have to eat the drywall and the fungus to get any of these symptoms. There is some evidence that touching the fungus may also cause problems.

Click here to read more from the Center for Disease Control about these cases in Cleveland

You have probably heard horror stories of people abandoning their homes, burning their houses down, and closing their schools, office buildings, and factories because of the presence of this fungus. In our opinion this is unwarranted. There are spores of fungi everywhere in this world. There are likely to be millions of spores in the room you're in right now, regardless of its general cleanliness. If you're reading this outside, there may be even more spores of many different kinds of fungi. The mere presence of Stachybotrys is not a reason for panic. You can read more from the CDC about Stachybotrys. has some great pages on Stachybotrys and indoor air quality. You can also vist this page by the EPA on indoor air quality

To learn more, you should also read this page on moulds from David Malloch's lab in Toronto.

Nik ZitomerThis month's FOTM co-author is Nik Zitomer, one of my graduate students. After receiving his BS degree from Penn State University in 2001, Nik has been working on a Master's degree in my lab on a pharmacognosy project.

We hope you learned something about Stachybotrys chartarum today. After reading this web page, you should be able to identify Stachybotrys (with the proper slides and microscope), as well as make informed decisions about the possible threat it may cause to human health.

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This page and other pages are © Copyright 2002 by Thomas J. Volk, University of Wisconsin-La Crosse.

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