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The Mould Fusarium: How Does It Affect Our Lives?

Fusarium species affect our lives in several areas.

In agriculture Fusarium is known to cause diseases of many economically important crop plants. Some species are known to colonize stored cereal grains not only causing losses but also producing mycotoxins such as trichothecenes, zearalenone, and fumonisins that are harmful to humans and animals(1, 3).

In the medical field, the species cause opportunistic infections of human eyes, skin or nails and may also cause systemic infections in individuals with weak immune system. The most important species as far as human infection is concerned are Fusarium solani, F. moniliforme (=Fusarium verticilloides), F. oxysporum and F. dimerum (1, 3). Fusarium solani is also allergenic and is occasionally found in indoor environments. It affects 4% of nasobronchial allergy patients (4).

Fusarium growing on agar media
Fusarium growing on agar media

Some of the infections attributed to some species of Fusarium are:

  • Fusarium keratitis
  • Onychomycosis (nail infection)
  • Certain skin infections
  • Fusarium osteomyelitis (bone and joint infections)
  • Pneumonia

In the industrial environment, Fusarium species are known to contaminate industrial products such as pharmaceutical solutions or machine cooling fluids. Fusarium keratitis has been in the news as the cause of severe fungal eye infections through contamination of contact lens solution.

Sampling for Airborne Spores of Fusarium Species

Fusarium species do not grow well at low water activity levels and will usually colonize very damp or wet material, hence, presence of Fusarium in a building is an indication of a water problem. Fusarium may produce three types of spores: namely, macroconidia, microconidia, and chlamydospores (3).

The macro and microconidia are the most likely to become airborne, but since they are produced in wet form they do not easily become aerosolized unless the mould is completely dry. Indoor airborne spore counts for Fusarium are therefore rarely high. A few spores of this fungus indoors could be an indication of serious mould growth.

Airborne microconidia and chlamydospores are difficult to identify and for air samples analysed by direct microscopy, only the macroconidia of some species may be reported. It is therefore possible that Fusariumspores (especially the microconidia) are usually lumped together with other unidentified spores.

Fusarium spores
Fusarium spores

For viable samples it is important to note that desiccation affects viability of Fusarium spores and therefore a few colony forming units (CFUs) would also be an indication of a problem.

According to Health Canada, persistent presence of significant numbers of Fusarium species and other toxigenic moulds such as Stachybotrys chartarum, Aspergillus and Penicillium requires further investigation (2).

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References

  1. Guarro, J., and J. Gene. 1992. Fusarium infections. Criteria for the identification of the responsible species. Mycoses 35:109-114
  2. Health Canada (1995). Indoor Air Quality in Office Buildings: A Technical Guide. A Report of the Federal-Provincial Advisory Committee on Environmental and Occupational Health.
  3. Nelson, P.E., Dignani, C.M., and Anaissie, E.J (1994). Taxonomy, Biology, and Clinical Aspects of Fusarium Species. Clinical Microbiology Reviews, 7(4): 479-504.
  4. Verma J, Sridhara S, Singh BP, Pasha S, Gangal SV, Arora N. (2001). Fusarium solani major allergen peptide IV-1 binds IgE but does not release histamine. Clin. Exp Allergy, 31(6):920-927.

Fusarium

Fusarium species exist as plant pathogens or saprophytes on plant debris and in soil.

Plant parasitic Fusarium causes wilting of many plants including crops such as tomatoes, bananas, sweet potatoes, pigeon peas, and pears. Some species of Fusarium are commonly isolated from seeds, especially those of cereals.

In addition, this common species of fungus can produce a number of different mycotoxins which include trichothecenes (T-2 toxin, HT-2 toxin, deoxynivalenol (DON) and nivalenol), zearalenone and fumonisins. The Fusarium species are probably the most prevalent toxin-producing fungi in the northern temperate regions and are commonly found on cereals grown in the temperate regions of America, Europe and Asia. These toxins have been shown to cause a variety of toxic effects in both experimental animals and livestock and are also suspected of causing toxicity in humans.

In indoor environments Fusarium species are generally found under very wet conditions. They are commonly isolated from carpet and mattress dust, damp walls, wallpaper, polyester polyurethane foam, humidifier pans and areas where stagnant water occurs in HVAC systems. Some species cause keratitis in humans, and infect eyes and finger nails. Fusarium species are also an inhalation hazard.

Fusarium culmorum

F. culmorum is soilborne and has a worldwide distribution. Indoors, it has been isolated from floor, carpet and mattress dust; damp wall and polyurethane foam.

Health Effects Associated With Fusarium culmorum

Fusarium culmorum is associated with allergy. It also produces vomitoxin, a trichothecene mycotoxin that causes a serious feed refusal and vomiting in animals fed contaminated feed.

Fusarium solani

F. solani is a soil borne fungus found indoors in carpet and mattress dust; damp walls, wallpaper; polyester polyurethane foam; insulating cotton in duct liner; water pipes and humidifiers.

Health Effects Associated With Fusarium solani

F. solani causes keratitis in humans. It is also associated with wounds and infections of the eyes and fingernails. It poses inhalation and deep skin (dermal) inoculation health risks to persons with weak immune systems. It also poses health risks related to major barrier breaks such as corneal perforation, major surgery, peritoneal or venous catheter presence, and injection drug use.

Fusarium verticillioides (fomerly called Fusarium moniliforme)

F. verticillioides is soilborne. Indoors, it is found on humidifier pans and other areas where stagnant water occurs in HVAC systems. Also found in mattress dust, and on damp walls.

Health Effects Associated With Fusarium verticillioides

F. verticillioides causes keratitis in humans and invasive mycoses in immunocompromised people. It poses inhalation and deep skin (dermal) inoculation health risks to persons with weak immune systems. F. verticillioides also poses health risks related to major barrier breaks such as corneal perforation, major surgery, peritoneal or venous catheter presence, and injection drug use.

You can learn more about our Fusarium mold testing service here.

Water Activity Requirements For Mold Growth

Definition of Water Activity

Water activity (aw) refers to “free” water available for microbial growth. For microbial growth to occur, moisture must be freely available. The water activity of a material determines which types of mold would grow on that material.

Technically, the water activity is defined as the ratio of the vapour pressure exerted by the water in the material to the vapour pressure of pure water at the same temperature and pressure.

Mold growth due to high water activity
Mold growth due to high water activity

Types of Mold based on Water Activity

Indoor molds vary in their water activity requirements and this ranges from 0.7 to >0.9. Higher aw materials tend to support the growth of more microorganisms. Unlike molds, bacteria usually require a water activity of at least 0.91 aw. Molds can be grouped according to their moisture requirements as follows:

  • Extremely to moderately xerophilic. These molds are the primary colonisers and they are capable of growth below 0.8 aw. Examples include Aspergillus and Penicillium
  • Slightly xerophilic. These molds are the secondary or intermediate colonisers. They are capable of growth between 0.8 and 0.9 aw. Examples of molds in this category include Altemaria and Cladosporium
  • Hydrophilic. Molds in this category are tertiary colonisers and require at least 0.9 aw for growth. Such high water activity can only be achieved through water intrusion and to a lesser extent high humidity and condensation. Examples of hydrophilic molds include Stachybotrys and Chaetomium

Note:

  1. Xerophilic means “dry loving.” Thus, xerophilic molds are those that can or prefer to grow in “dry” environments. “Dry” is used here in relative sense since no mold can grow in a completely dry environment.
  2. Hydrophilic means “water loving.” Thus, hydrophilic molds are those molds that require very high levels of moisture to grow.

Indicators of Water Damage

Water damage may occur over many months, mainly through roof leakage, but also via rising damp and defective plumbing, which result in mold growth. Indoor molds as well as bacteria are usually saprophytic, meaning that they obtain nutrients from dead organic matter. The nutrients are from the breakdown of simple to complex sugars such as starches, cellulose and pectin. The materials most susceptible to mold growth are organic materials containing cellulose (i.e. jute, wallpaper, cardboard and wooden materials). The tertiary colonisers are used as the indicators of moisture damage. The table below shows some of the most common indicators of water damage in buildings.

Indicators of excessive moisture or chronic condensation

Molds indicative of moisture or chronic condensation in a building
Alternaria alternata Phialophora sp
Aspergillus fumigatus Fusarium sp.
Chaetomium spp Ulocladium sp.
Trichoderma (some species) Yeasts (Rhodotorula spp.)
Exophiala sp. Memnoniella echinata
Stachybotrys chartarum
(synonym S. atra)

What is Aspergillus fumigatus?

Aspergillus fumigatus is a thermotolerant/thermophilic fungus capable of growing over a wide temperature range (12°C–53°C). It has a worldwide distribution. Being thermotolerant, it is a significant component of compost microflora.

Health effects associated with Aspergillus fumigatus

The spores of Aspergillus fumigatus are very small. Having a diameter of 2–3.5 µm, they are easily inhaled deep into the lungs. It is estimated that people inhale at least several hundreds of spores of Aspergillus fumigatus per day without harm. However, Aspergillus fumigatus is an opportunist pathogen (Hazard Risk Group 2) and can cause a lung infection (aspergillosis), in people with weak immune system. Most of the cases of aspergillosis are caused by this fungus. Because of its potential role as an opportunist pathogen, there is concern about high concentrations of Aspergillus fumigatus spores in the vicinity of hospitals, where those with compromised immune system such as organ transplant and cancer patients, may be at increased risk of infection. Therefore, monitoring for airborne spores in hospitals especially during renovations is a good practice.

Aspergillus fumigatus
Aspergillus fumigatus

Occurrence of Aspergillus fumigatus

Aspergillus fumigatus naturally occurs in decaying organic material, but because it is a thermotolerant fungus it grows well at raised temperatures experienced during the composting process. Within the indoor environment, A. fumigatus belongs to the group of indicator microorganisms typical of moisture-damaged buildings such Stachybotrys, Chaetomium, Fusarium and Ulocladium. The following characteristics make A. fumigatus a ubiquitous opportunistic pathogen: 1) ability to survive and grow in a wide range of environmental conditions, 2) effective dispersal in the air, 3) physical characteristics that allow spores to reach deep into the respiratory system, and 4) ability to swiftly adapt to the host environment.

Air Sampling for Aspergillus fumigatus

In hospital environment, air sampling may be conducted to monitor air quality during construction, to verify filter efficiency, or to commission new space prior to occupancy. Because aspergillosis cases have occurred when airborne fungal spore concentrations ranged as low as 0.9–2.2 colony-forming units per cubic meter (CFU/m3) of air, it is suggested that an air volume of at least 1000 L (1 m3) should be considered when sampling highly filtered areas.

Sampling media and incubation temperature for Aspergillus fumigatus

Malt extract agar (MEA) can be used to sample for Aspergillus fumigatus. For selective isolation of A. fumigatus, a high incubation temperature of 37 to 40 is then used as this inhibits growth of other saprophytic fungi.

References

  1. Kwon-Chung, K. J., & Sugui, J. A., 2013. Aspergillus fumigatus—What Makes the Species a Ubiquitous Human Fungal Pathogen? PLoS Pathogens, 9(12), e1003743. http://doi.org/10.1371/journal.ppat.1003743
  2. Sehulster, L. et al., 2003. Guidelines for environmental infection control in health-care facilities. Morbidity and Mortality Weekly Report Recommendations and Reports RR, 52(10).
  3. Swan, J. et al., 2003. Occupational and environmental exposure to bioaerosols from composts and potential health effects: a critical review of published data, HSE Books.
  4. Streifel, A. et al., 1983. Aspergillus fumigatus and other thermotolerant fungi generated by hospital building demolition. Applied and environmental microbiology, 46(2), pp.375–378.

Mold Spores In Air And Health Issues

Mold spores are tiny structures produced by molds for the purpose of reproduction, i.e., they are “seeds” but unlike the plant seeds mold spores do not contain a preformed empryo.

Health Effects Associated With Mold Spores

Mold spores
Mold spores

Mold spores are common in household and workplace dust. Also, due to their light weight, mold spores are often floating in the air both outdoors and indoors. Inhaling mold spores may cause allergic reactions in sensitive individuals. Allergic responses include hay fever-type symptoms, such as sneezing, runny nose, red eyes, and skin rash (dermatitis). Allergic reactions to mold spores are common. They can be immediate or delayed. Mold spores can also cause asthma attacks in people with asthma who are allergic to mold.

We breathe in mold spores and fragments every day, indoors and outdoors. Usually these exposures do not present a health risk. However, health problems may result when people are exposed to large amounts of mold, particularly indoors.

In about 20 percent of people, the immune system overreacts and causes the allergic response resulting in symptoms such as runny nose, scratchy throat and sneezing. Most of us know this allergic illness as “hay fever” or “allergic rhinitis.”

If you have an allergy that never ends when seasons change, you may be allergic to mold spores. Allergic symptoms from outdoor mold spores are most common in summer.

How do I get rid of mold spores

It is impossible to get rid of all mold spores indoors; some spores will be found floating through the air and in house dust. However we can reduce the amount of spores in our homes by controlling mold growth. The mold spores will not grow if moisture is not present. Therefore, indoor mold growth can and should be prevented or controlled by controlling moisture indoors. If there is no mold growth indoors then the only source of spores would be outdoors. Spores originating from outdoors may not be in amounts that would present a health problem. If there is mold growth in your home, you must clean up the mold and fix the water problem. If you clean up the mold, but don’t fix the water problem, then, most likely, the mold problem will come back.

Common Allergy Causing Mold Spores

Although there are many types of molds, only a few dozen are known to cause allergic reactions. Alternaria, Cladosporium, Aspergillus, Penicillium, Helminthosporium, Epicoccum, Fusarium, Mucor, Rhizopus and Aureobasidium are the major culprits. Some common mold spores can be identified easily in a laboratory when viewed under a microscope.

Mold spores Release

The spores can be actively released or passively released depending on the type of mold. The release of spores is also influenced by environmental conditions. Some spores are released in dry, windy weather. Others are released with the fog or dew when humidity is high.

Air Sampling For Mold Spores

Indoor air sampling for mold is important for several reasons. Mold spores are not visible to the naked eye and the only way to determine whether the air is contaminated and the types of mold present is through laboratory analysis of the air samples. Having air samples analyzed can also help provide evidence of the scope and severity of a mold problem, as well as aid in assessing human exposure to mold. After mold removal, new samples are typically taken to help ensure that the amount of airborne mold spores has been successfully reduced.

Air samples can be used to gather data about mold present in the interior of a house. Samples are taken using a pump that forces air through a collection device which catches mold spores. The sample is then sent off to a laboratory to be analyzed.

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