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Alternaria And Other Mould Spores As Causes Of Allergy

As far back as 1924 Prof Dr Willem Storm van Leeuwen from The Netherlands suggested that inhaled mould spores such as those of Alternaria could cause asthma. The types of moulds widely known to cause respiratory allergy in humans include Aspergillus, Penicillium, Cladosporium and Alternaria. The allergic responses are mainly due to the inhalation of spores rather than mycelial/hyphal fragments. Allergic reactions to each spore type differ between individuals. Mould allergens also vary in the severity of the allergic reactions they induce. More people, for example, are more sensitive to Alternaria than to Cladosporium. Alternaria also produces more severe reactions, while Cladosporium generally only produces a mild reaction. Cladosporium and in particular Cladosporium herbarum, are often the major contributors to outdoor air-spora. Due to their high concentrations they are a major cause of inhalant allergy and allergic asthma in humans. Occupational pulmonary diseases are common in cheese industry (Penicillium roquefortii), breweries (Aspergillus clavatus) and in mushroom farms (Doratomyces sp).

Alternaria is cosmopolitan and ubiquitous in nature. It is currently comprised of about 40-50 species. Alternaria is a well recognized plant disease causing agent. Species of Alternaria are commonly isolated from dead plant materials, soil, food, and indoor air. Alternaria alternata has been isolated from numerous kinds of organic materials in damp situations, including textiles, stored food, canvas, cardboard and paper, electric cables, polyurethane, jet fuel, sewage and effluents. Airborne spores of Altenaria alternata and A. tenuissima are found in very high numbers in the outdoor environment during fall.

Spores of Alternaria alternata as seen under a microscope Alternaria alternata is a well recognized allergen with airborne spores and mycelial fragments being responsible for the allergic symptoms in individuals with rhinitis or bronchial asthma. Alternaria sensitivity can also lead to severe and potentially fatal asthma. Studies have shown that up to 70 % of mould-allergic patients have skin test reactivity to Alternaria. It has also been shown that prolonged heavy exposure to Alternaria alternata spores and mycelial fragments mimics that of other allergens such as cat dander and dust mites. Since Alternaria is a seasonal mould then this type of allergy is more prevalent in the fall. A. alternata has also been recorded as an opportunistic pathogen causing skin diseases particularly in immunocompromised patients such as the bone marrow transplant patients.

The presence of Alternaria together with other moulds such as Ulocladium spp and Phoma spp, in indoor environment is indicative of humid conditions. Alternaria alternata is not commonly isolated from indoor building materials and in most instances spores found in indoor air environment may have originated from outdoor sources. A closely related mould, Ulocladium chartarum, which is very common in indoor environment is frequently misidentified in labs as Alternaria alternata. U. chartarum is common on wallpaper and drywall, and has been isolated from emulsion paint, polyurethane, plywood and manila fibre.

Should you have a question on Alternaria or any other mould, please send it to My Question.

What Are Some Of The Mycotoxins Producing Indoor Moulds?

Jackson Kung'u

Growth of mould on building materials is determined by the water activity (a_w) among other factors. The a_w is a measure of the moistness of the material. Some moulds are capable of growing over a wide range of a_w but there is always an optimal range. While these moulds grow, they reach a stage when they produce mycotoxins depending on the growth conditions. Some of the indoor moulds that produce mycotoxins are discussed below.

Stachybotrys chartarum
Stachybotrys chartarum is cosmopolitan and grows naturally on straw and other cellulose containing materials in soil. In the indoor environment, this mould is commonly found together with other water-loving moulds on cellulose containing materials including paper, canvas and jute which are wetted to a water activity > 0.98. Stachybotrys chartarum produces a number of mycotoxins inclduding macrocyclic trichothecenes, satratoxins and roridins when growing on building materials. The optimum temperature for growth of Stachybotrys chartarum is 23 ^oC with a minimum and maximum temperature of 2 and 37 ^oC respectively. The optimal water activity is 0.98 with a minimum at 0.89.

Aspergillus flavus
Aspergillus flavus is widely distributed in soil. It is associated with a wide range of stored products such as maize and nuts. In indoor environment it is commonly found on damp walls, wallpaper, floor and carpet dust, tarred wooden flooring, humidifiers and HVAC fans, bakeries, shoes, leather, and bird droppings. Strains of this mould may produce mycotoxins such as aflatoxin, a class 1 carcinogen. The minimum and maximum temperatures for growth are 6 and 45 ^oC, with an optimum at 40 ^oC. The minimum water activity is 0.78 and an optimum at 0.98.

Aspergillus fumigatus
Aspergillus fumigatus is common in composting plant material, woodchips and garbage. Also common in dust infiltrating from outdoor air, carpet and mattress dust, wet building and finishing material, HVAC insulations, fans, filters, humidifier water and potted plant soil. A. fumigatus is a producer of various mycotoxins including gliotoxin, verrucologen, fumitremorgin A & B and fumigaclavines among others. A. fumigatus has an optimum growth temperature at 43 ^oC and minimum and maximum at 10 and 57 ^oC respectively. Minimum water activity for A. fumigatus is 0.82 and the optimum is 0.97.

Aspergillus niger
Aspergillus niger is found worldwide in soil and plant litter. In indoor environment A. niger is common in floor, carpet and mattress dust, acrylic paint, UFFI, leather, HVAC filters and fans, and potted plant soil. A. niger produces mycotoxins such as malformins and a few strains also produce ochratoxin A. A. niger requires a minimum temperature for growth of 6 and maximum of 47 ^oC with an optimum at 37 ^oC.

Aspergillus versicolor
Aspergillus versicolor is very common on gypsum board, floor, carpet, mattress and upholstered-furniture dust, and damp walls. A. versicolor produces high quantities of the carcinogenic mycotoxin, sterigmatocystin at water activities (a_w) above 0.95. A. versicolor is generally xerophilic- meaning that it can grow at low water activity (< 0.8). The minimum and maximum growth temperatures for A. versicolor are 4 and 40 ^oC with an optimum at 30 ^oC. Its optimal water activity is 0.95 with a minimum at 0.75.

Penicillium chrysogenum
Penicillium chrysogenum is one of the most common indoor moulds. It’s not known to produce highly potent mycotoxins. It is extremely common on damp building materials, walls and wallpaper; floor, carpet mattress and upholstered-furniture dust. P. chrysogenum produces few detectable metabolites and often none when growing on building materials. Lack of observed effects on persons exposed to high quantities of spores and the production of few metabolites suggest this species may not be an important health hazard. However, some strains may cause allergenic reactions to susceptible individuals. P. chrysogenum can grow at a minimum temperature of -4 ^oC, an optimum of 28 ^oC, and a maximum of 38 ^oC. It has minimum water activity of 0.79 and an optimum at 0.98

Penicillium brevicompactum
Penicillium brevicompactum is common on damp walls and building materials e.g., gypsum board; floor, carpet, mattress and upholstered-furniture dust. P. brevicompactum produces mycophenolic acid. P. brevicompactum can grow at -2 and 30 ^oC with an optimum at 25 ^oC. Its water activity requirements are a minimum of 0.75 and an optimum at 0.96.

Chaetomium globosum
Chaetomium globosum is common on cellulose containing building materials that has been very wet such as gypsum board, cellulose board and wood. Species of the genus Chaetomium are known to produce mycotoxins. C. globosum produces high quantities of chaetoglobosins. C. globosum requires a water activity of >0.90.

Trichoderma species
Trichderma species are frequently found on gypsum board and water saturated wood; floor, carpet and mattress dust; paint; domestic water supply, and HVAC system air. In one study, Trichoderma species were not found to produce detectable quantities of trichothecenes when growing on building materials. Less than 1% of the isolates produced trichodermol or its esters.

References
Kuhn, D. M. and Ghannoum, M. A. (2003). Indoor Mold, Toxigenic Fungi, and Stachybotrys chartarum: Infectious Disease Perspective. Clinical Microbiology Reviews, 16(1):144–172.Nielsen, K.F, (2002).

Mould growth on building materials: Secondary metabolites, mycotoxins and biomarkers, Dissertation, The Mycology Group, Technical University of Denmark. 116p

Should you have a question concerning mycotoxins or indoor moulds or bacteria, please send your question to My Question.

The Mould Aspergillus: How Does It Affect Our Lives?

Jackson Kung'u

Aspergillus has close to 200 species and varieties. This mould is widely distributed from the arctic region to the tropics and is frequently found in air, soil, and stored agricultural products. It’s also very common in damp basements.

Heads and spores of Aspergillus fumigatus as seen under a microscope Harmful effects of Aspergillus to our lives

Species of Aspergillus produce dry, hydrophobic spores that are easily inhaled. Inhaling spores of Aspergillus, particularly those of Aspergillus flavus and Aspergillus fumigatus frequently cause pulmonary aspergillosis, either allergic, or invasive or a combination of the two. A. flavus produces the highly potent mycotoxin called aflatoxin which over the years has been reported as the cause of death in humans and animals. In 2004 aflatoxin killed over 100 people in an East African country who consumed grains infested by A. flavus. Many other species of Aspergillus such as A. clavatus, A. niger, and A. versicolor are also known to be toxigenic or allergenic. Instant action is required when growth of these moulds appear in occupied indoor environment.

Because of their ability to produce a large number of enzymes, species of Aspergillus are capable of utilizing an enormous variety of organic material for food. Therefore, under humid conditions, it will grow on leather, cloth fabrics and books reducing their value and imparting musty odour to these items. Several species are frequently found on grains and exposed foodstuffs where they cause decay and subsequent loss of food.

A culture of Aspergillus flavus Occurrence of Aspergillus species in indoor environment
Species of Aspergillus have been isolated from damp walls, wallpaper, PVC/paper wall covering, gypsum board, floor, carpet and mattress dust, upholstered-furniture dust , acrylic paint, UFFI, leather, HVAC insulations, filters and fans, humidifier water, shoes, leather, bird droppings, potted plant soil, plastic and decomposing wood.

Aspergillus fumigatus is frequently found in kitchens and bathrooms while in mattresses and carpets, Aspergillus versicolor and Aspergillus repens are common. A. versicolor and A. fumigatus are also common in basements. Species frequently found in flower pot soil are A. fumigatus, Aspergillus niger and Aspergillus flavus.

Generally the amount of airborne spores of Aspergillus spp. in indoor air is higher than outdoors at any given time. In the home, the amount of airborne spores is significantly increased when cleaning is carried out mechanically, for example, when carpets are vacuum cleaned.

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Which Moulds Grow in Buildings And Why Do They Grow?

Jackson Kung'u

The level of moisture (usually referred to as water activity) in building material determines not only whether mould will grow or not but also the types that colonize the material. Damp materials with a water activity value equal to or greater than 0.90 are usually colonized by strains of Aspergillus fumigatus, Trichoderma spp., Exophiala spp., Stachybotrys spp., Phialophora spp., Fusarium spp., Ulocladium spp., and yeasts such as Rhodotorula spp. Materials with a water activity value ranging from 0.90 – 0.85 are colonized by Aspergillus versicolor while those with water activity values of 0.85 or slightly less are colonized by Aspergillus versicolor, Eurotium spp., Wallemia spp., and Penicillium spp., such as Penicillium chrysogenum and Penicillium aurantiogriseum.

Water leakage through roofs, defective plumbing installations and condensation are the main sources for water damage with subsequent mould growth. The building materials most susceptible to mould attacks are water damaged, aged organic cellulose containing materials such as wood, jute, wallpaper, and cardboard. Moulds that are most frequently encountered in buildings are Penicillium (68%), Aspergillus (56%), Chaetomium (22%), Ulocladium (21%), Stachybotrys (19%), Cladosporium (15%), Acremonium (14%), Mucor (14%), Paecilomyces (10%), Alternaria (8%), Verticillium (8%), and Trichoderma (7%). These moulds are all known to cause different types of inhalation allergy.

Do you have a question concerning indoor moulds? Send it to us at My Question.

Alternaria And Other Mould Spores As Causes Of Allergy

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The Mould Aspergillus: How Does It Affect Our Lives?

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