Extracts from Berlin D.
Nelson: Professor,
Department of Plant Pathology, North Dakota State University, Fargo
Stachybotrys
chartarum:The Toxic Indoor Mould:
is a fungus that has become
notorious as a mycotoxin producer that can cause animal and human
mycotoxicosis. Indeed, over the past 15 years in North America, evidence
has accumulated implicating this fungus as a serious problem in homes
and buildings and one of the causes of the "sick building syndrome." In
1993-1994, there was an unusual outbreak of pulmonary hemorrhage in
infants in Cleveland, Ohio, where researchers found S. chartarum
growing in the homes of the sick infants. This incident increased the
awareness of home/building molds and brought this fungus to the
immediate attention of the medical community. In recent years there has
been a cascade of reports about toxic molds in the national media. The
New York Times Magazine, August 12, 2001, ran a front page story on
toxic mold. Newspaper articles (Fig. 1) such as "Fungus in 'Sick'
Building" (New York Times, May 5, 1996) or "Mold in schools forces
removal of Forks kids" (Fargo Forum, June 1997) are eye-catching news
items. The nationally syndicated comic strip Rex Morgan ran a series on
Stachybotrys, and television news shows have run entire programs
on Stachybotrys contamination of homes. The fungus has resulted
in multimillion dollar litigations and caused serious problems for
homeowners and building managers who must deal with the human issues and
remediation.
As a
mycologist, I have been advising public officials and the general public
on the issues concerning indoor moulds. Our region experienced one of
the greatest natural disasters of modern times when the Red River
flooded in 1997. In Grand Forks, ND, alone, there were 9,000 flooded
homes. There was an enormous need for information on the effects of the
flood on human health in the Red River Valley. Because of the increasing
awareness of moulds in indoor air quality, a coordinated effort by city,
state and federal officials to provide information on mould prevention
was undertaken. In my observations following the flood and in subsequent
years of dealing with indoor mould issues, I have been impressed with
the common occurrence and extensive growth of S. chartarum in
homes and buildings damaged by flood waters or other types of water
incursions and the lack of knowledge by the general public and public
and private institutions about this fungus. This review provides
information on the fungus, its biologically active compounds, the
history of the problem, the controversy about this fungus, and briefly
comments on detection and remediation.
A Conidium :
The Fungus :
The mass of conidia :
Stachybotrys chartarum The fungus is
relatively easy to identify because of the unique phialides of the genus
and conidial morphology of the species. Conidiophores are determinate,
macronematous, solitary or in groups, erect, irregularly branched or
simple, septate, dark olivaceous, and often rough walled on the upper
part. The phialides are large, 9-14 µm in length, in whorls, ellipsoid,
olivaceous, and often with conspicuous collarettes. Conidia are
ellipsoidal, unicellular, 7 to 12 by 4 to 6 µm, dark brown to black and
often showing a ridged topography when mature. The ridged nature is
readily apparent with scanning electron microscopy (Figs. 3 and 4), but
can also be observed with an oil immersion lens at 1000x. On lower power
the spores appear verrucose. Young spores and some mature spores may be
smooth. The phialides produce conidia singly and successively into a
slime droplet that covers the phialides. Eventually the slime dries and
the conidia are covered with the slime residue and remain on the
conidiophore as a mass or ball of spores (Fig. 3). The spores are
therefore not readily disseminated in the air compared to other fungi
such as Aspergillus. However, when the fungus and substrate dries
and is disturbed by mechanical means or air movement, conidia can become
bioaerosols. A genus similar to Stachybotrys, but with spores in
chains is Memnoniella (38); it also has species that produces
trichothecenes (35). Haugland et al. (21) have proposed relegation of
Memnoniella to synonymy with Stachybotrys based on
morphological characteristics and comparative sequence analysis of the
nuclear ribosomal RNA operon.
Between the
1950s and the 1980s there were continued publications on S. chartarum
but none that indicated a potential problem with S. chartarum in
homes and buildings. In 1986, Croft et al. (6) reported an outbreak of
trichothecene toxicosis in a Chicago home. Over a 5-year period, the
family complained of headaches, sore throats, flue symptoms, recurring
colds, diarrhoea, fatigue, dermatitis, and general malaise. Air sampling
of this home revealed spores of S. chartarum. The fungus was
found growing on moist organic debris in an un-insulated cold air duct
and on some wood fibre ceiling material. The home had a chronic moisture
problem that favoured mould growth.
Do not let your
greatest asset get to this stage:
