By Murali Putty, EMLab P&K Analyst
Pithomyces is a soil borne ubiquitous fungus; cosmopolitan in nature. The genus Pithomyces contains more than 40 species, occurring on dead leaves of more than 50 different plants, especially in leaf fodders, soil and grasses. It is rarely found growing indoors, but can grow on paper under the right conditions. It has also been reported from ceiling tiles, carpet and mattress dust.
Colonies of Pithomyces are fast growing on general fungal media. Surface color of the colony is pale to dark brown and the reverse is dark brown. Pithomyces colonies have cottony texture and the sporulation is slow. The spores are multicellular and deeply pigmented. Distinctive features are the presence of both transverse and longitudinal divisions, called septa. The shape of the spores varies from barrel-shaped, to ellipsoid, to club-shaped.
Figure 1: Microscopic photo of Pithomyces.
Copyright © 2011 EMLab P&K
Figure 2: Microscopic photo of Pithomyces.
Copyright © 2011 EMLab P&K
Spores of Pithomyces occur individually in air samples. In spore traps, Pithomyces chartarum are recognizable as distinctive, multicelled, brown spores. Pithomyces chartarum is characterized by hand grenade-shaped spores with longitudinal septa and usually three transverse septa. Other species of Pithomyces are common but can be difficult to identify. Spores of Pithomyces may be confused with younger spores of Alternaria and Ulocladium, however in tape lift samples, they are distinctive.
From over 250,000 samples collected across the U.S. throughout the year, recovery rates of Pithomyces vary from about 4% in March to 32% in August. They are most frequently recovered in the months of August, September and October and the lowest recovery rates are in the months of February, March and April (Figure 3). The state with the highest recovery rate (percentage of samples that have Pithomyces) is Indiana with 38%, while Nevada State had the lowest rate of recovery of 1.8%.
Figure 3: Frequency of detection for Pithomyces.
Source: EMLab P&K MoldRANGE™ data. Copyright © 2011 EMLab P&K
Spores of Pithomyces have demonstrated much allergenic activity in several reports, however the details of such activity are unpublished. Pithomyces chartarum occurs worldwide but is a problem predominantly in New Zealand where farm animals are intensively grazed. Several isolates of P. chartarum produce the alkaloid mycotoxin sporidesmin, which causes facial eczema in sheep. It also produces cyclodepsipeptides and sporidemolides mycotoxins. The spores of the fungus release the mycotoxin sporidesmin in the gastrointestinal tract, causing a blockage in the bile ducts that leads to injury of the liver. Bile, chlorophyll and other waste products consequently build up in the sheep bloodstream causing photosensitivity of the skin, especially that exposed to direct sunlight. This in turn causes severe skin irritation that the animal attempts to relieve by rubbing its head against available objects, resulting in peeling of the skin. Sporidesmin can lower an animal's immunity and affect total production in farm animals. When ingested in larger quantities, it can result in death. Effects of these mycotoxins on human health is unknown.
The percentage of fungal strains producing this toxin varies in different countries. Toxigenic strains predominate in New Zealand and Australia, whereas non-toxic strains prevail in North and South America. Pithomyces chartarum is also said to be involved in a glume blotch disease of rice.
1. Collin R.G., E. Odriozola and N.R. Towers. 1998. Sporidesmin production by Pithomyces chartarum isolates from Australia, Brazil, New Zealand and Uruguay. Mycological Research 102: 163-166.
2. Domsch, K.H., W. Gams and T.H. Anderson. 1993. Compendium of Soil Fungi. Vol. I. IHW-Verlag, Germany. pp 657-659.
3. Flannigan, B., R.A. Samson and J.D. Miller. 2001. Microorganisms in Home and Indoor Work Environments, Taylor & Francis, London.
4. Dennis Kunkel Microscopy: Hyphae and fruiting structures/conidiophores (Pithomyces sp.)
5. EMLab P&K: Pithomyces
6. Wikipedia: Facial Eczema
7. University of Adelaide: Pithomyces sp.
8. University of Tulsa: Pithomyces
9. Menna, M.E. Di, B.L. Smith and C.O. Miles. 2009. A history of facial eczema (pithomycotoxicosis) research. New Zealand Journal of Agricultural Research 52(4): 345-376.
10. Toth B., M. Csosz, J. Dijksterhuis, J.C. Frisvad and J. Varga. 2007. Pithomyces chartarum as a pathogen of wheat. Journal of Plant Pathology 89: 405-408.
11. Yang, C.S. and P. Heinsohn. 2007. Sampling and analysis of indoor microorganisms. John Wiley & Sons, Hoboken, New Jersey. pp 255.
This article was originally published on March 2011.