People are exposed to aeroallergens in a variety of settings, both at home and at work. Fungi are ubiquitous airborne allergens and are important causes of human diseases, especially in the upper and lower respiratory tracts. These diseases occur in persons of various ages.
Airborne spores and other fungi particles are ubiquitous in nonpolar landscapes, especially amongst field crops, and often form the bulk of suspended biogenic debris. The term mold often is used synonymously with the term fungi. A more precise definition would specify that molds lack macroscopic reproductive structures but may produce visible colonies. Respiratory illness in subjects exposed to rust and dark-spored imperfecti fungi was described more than 60 years ago, and physicians worldwide now recognize a sensitization to diverse fungi.
Since fungus particles commonly are derived from wholly microscopic sources, exposure hazards are assessed largely through direct sampling of a suspect atmosphere. Because of their small size, fungal emanations present special collection requirements to ensure particle viability for culture-based studies.
Fungi have two basic structures. Yeast grows as single cells by central division of eccentric budding to form daughter units. Most other familiar fungi are composed of branching threads, 3-10 mcm in width, termed hyphae. A mycelium is an aggregate of hyphae. Hyphae are modified to bear the simple reproductive parts of many microfungi and form the structural tissue of fleshy fungi (eg, mushrooms, puff balls).
In general, familiar allergenic molds reproduce asexually. However, two large and distinctive classes, Ascomycetes and Basidiomycetes, also produce innumerable sexual spores for atmospheric dispersion. In its life cycle, a single fungus organism produces both sexual and asexual spores from morphologically different structures, respectively termed perfect and imperfect stages.
Statistics of Occurrence
There are 35 million persons with sinus problems and 15 million persons with asthma reported in the United States alone. Clinically, physicians know that a sinus infection can contribute significantly to the frequency and severity of asthma attacks.
Toxicity of Mold and Physiology of Affectation
The physiology of mucus in individuals with asthma is similar to that of nasal mucus. Mucociliary clearance (MCC) involves cilia and the layers of mucus on the ciliated epithelium and refers to the movement of particles along a desired path for maximum health. In the upper respiratory tract, cilia propel the mucus and its trapped bacteria and particles to the nasopharynx, where it drops to the hypopharynx and is swallowed. The stomach acid then disposes of the unwanted invaders.
In the lower respiratory tract, the cilia that line the trachea and bronchial tree similarly move the mucus blanket up the trachea and into the hypopharynx for swallowing.
The science of rheology investigates the makeup of this liquid and studies its viscosity and elasticity. Two layers of mucus are present over the ciliated cell; an outer, thick, viscoelastic, semisolid mucus layer, which the cilia do not strike directly, is found over a layer of watery serous fluid. Due to the lowered viscosity of the layer of watery serous fluid, the cilia are able to beat normally and to move the watery lower layer, thereby, affecting movement of the upper thick layer. Changes in these properties affect movement of the mucus blanket and play a major role in pulmonary and sinus disease. If the movement of the blanket is slowed, bacteria are able to multiply as the mucus thickens and stagnates.
Mold Infectious Processes
Fungal exposure can also come from a volatile compound (VOC) that a fungi or mold creates through primary or secondary metabolism that then becomes airborne. Note that primary metabolic processes are those necessary to sustain the life of an organism. These volatile compounds may be constantly created as the fungus consumes its food source during the primary metabolic process. VOCs can irritate the mucous membranes of the eyes and respiratory system.
Fungi that consume certain organic sources can release highly toxic gases. For example, a fungus that grows on wallpaper often releases toxic gas arsine directly from the wallpaper that contains arsenic pigments. Thus, fungi and molds can release dangerous materials when they break down the host material. This can cause mucous membrane irritation in sensitized individuals.
Research is demonstrating that fungal-volatile compounds may impact the "common chemical sense" which senses pungency and responds to it. This sense is primarily associated with the trigeminal nerve. The sensory and motor nerves respond to pungency by trying to hold the breath, discomfort, or through sensations such as itching, burning, and skin crawling. Changes in sensation, swelling of mucous membranes, constriction of the respiratory smooth muscle, or dilation of surface blood vessels may be part of fight or flight reactions in response to trigeminal nerve stimulation.
Reactions often include a reduced attention level, general disorientation, lowered reflex time, dizziness, headache, burning sensation in the mucosa, and so on.
Volatile compounds found in or around homes can be responsible for mucous membrane irritants. It is now believed that fungi can add to the already existing compounds when breaking down certain organic substances. A mold-contaminated building may have a significant contribution from fungal contaminants that are added to common VOCs (e.g., building materials, paints, plastics, and cleaning chemicals).
VOCs in general can result in symptoms that include lowered attention span, headaches, lack of concentration, and dizziness.
Reaction to Mold Odors
Some individuals have very strong reactions to the smells given off by molds. Among humans, there is a high degree of variation in ability to detect these odors. Certain individuals can detect low levels of VOCs, while others can only detect relatively high levels. Those individuals who are particularly susceptible to mold odors may react with headache, nasal stuffiness, nausea, or even vomiting.
Asthmatics often exhibit extreme symptoms when exposed to certain mold-induced odors.
Molds also produce secondary metabolites such as antibiotics and poisonous substances produced by a fungus known as mycotoxins. Sometimes it is possible to isolate antibiotics from the molds themselves in order to utilize some of their properties in fighting infections.
Secondary metabolisms are not necessary for maintaining the existence of a mold - either by creating energy or synthesizing structural components, informational molecules, or enzymes. They do, however, function to provide molds with advantages over other mold and bacteria and are toxic to certain plant and human cells.
Toxic conditions exist when a human is exposured to these mycotoxins - either through ingesting mycotoxin-containing mold spores or with skin contact to toxic mold itself.
Mycotoxins are nearly all cytotoxic (substances produced by microorganisms that are toxic to individual cells), which disrupt various cellular structures such as membranes, and interrupt important processes, including protein, RNA, and DNA synthesis.
Mycotoxins vary in the danger they pose for humans. Mycotoxins pose a threat to larger organisms, not because they are specifically targeting them, but rather because these large organisms inadvertently come across the byproduct of the competing molds all battling for the same ecological niche.
Numerous mold types produce mycotoxins, including some found indoors in contaminated homes and office buildings. Another factor that determines the mycotoxins that are produced by specific molds usually depends on the materials or organisms that they grow on.
It used to be thought that dangerous molds were primarily contaminants in foods. This notion is quickly changing. Recently, researchers have become more concerned with multiple mycotoxins that develop from many types of mold spores growing in moist indoor environments.
Health effects from exposures to such mold mixtures can differ from those related to single mycotoxins in controlled laboratory exposures. Although it is difficult to predict how exposure to multiple toxigenic molds can affect an individual - a synergetic effect can occur - the following table provides possible poor health effects from mycotoxin exposure to multiple molds indoors.
Increased vascular fragility, the possibility of hemorrhaging into body tissues.
Possible molds include: aflatoxin, satratoxin, and roridins
Respiratory distress, hemorrhaging from the lungs and surrounding lung tissues
Rash, burning sensations, sloughing of skin
Painful and burning urination, increase in infections of the urethra, bladder, and kidneys
Infertility and changes in the reproductive cycles, menses, and sperm motility
Many mycotoxins can produce changes or weakenings of the immune system and can shorten the life span of those with compromised immunity systems (i.e, HIV / AIDS).
Table 1.1. Mycotoxins and their effects on human physiology
Unfortunately, not all types or species of molds have been tested for the presence of mycotoxins. The production of toxins varies according to the type of mold, the substrate on which it grows, and seasons of the year.
National Allergy Bureau
This agency considers mold counts in the air 0-900 as low, 2500 as moderate, 25,000 as high, and above 25,000 as very high. At "high" levels most individuals with any sensitivity will experience symptoms. Acceptable levels for individual species vary since species toxicity varies widely as does spore size, weight,…