Aerosolized
Aspergillus spores are found nearly everywhere so we are routinely and almost constantly exposed to them. Such exposure is a normal part of the human condition and generally poses no adverse health effects. Nevertheless,
Aspergillus can and does cause animal disease in three major ways: through the production of mycotoxins; through induction of allergenic responses; and through localized or systemic infections. With the latter two categories, the immune status of the host is pivotal. Allergies and asthma are thought to be caused by an active host immune response against the presence of fungal spores or hyphae. In contrast, with invasive aspergillosis, the immune system has collapsed and little or no defence can be mounted.
Suggested reading: Microbial Toxins: Current Research and Future TrendsAllergies and asthma
Atopy is a genetic predisposition to developing certain hypersensitivity reactions such as asthma, hay fever (allergic rhinitis), and food allergies. Allergic reactions to
Aspergillus in atopic individuals can be caused by fungal spores in the air and from fungi ingested in food. Airborne spores are readily inhaled when we breathe; they also come into contact with the eyes and other exposed parts of the body. Moulds are involved in the initiation and exacerbation of lower airway diseases such as asthma, although the specific aetiology is poorly understood.
The level of spore inhalation varies enormously with local environmental conditions. Certain environments like compost heaps and barns have unusually high concentrations. Massive exposure, even among individuals who are not allergic or asthmatic, should be avoided because repeated contact with large doses of fungal spores may induce allergic alveolitis, in which a lymphocyte-directed hypersensitivity reaction occurs. Extrinsic allergic alveolitis is not limited to
Aspergillus or even fungal spores, but is caused by the inhalation of antigenic dusts. These dusts are rarely if ever composed of one organic substance but tend to be a variable mixture of fungal and actinomycete spores, animal proteins and other organic matter. 'Occupational mycoses' are forms of extrinsic allergic alveolitis They are all inflammatory reactions caused by breathing high concentrations of mould spores and other antigenic organic matter. Some forms of these illdefined human diseases have been associated particularly with exposure to high concentrations of
Aspergillus spores, including farmer's lung, malt worker's lung, compost lung and bird fancier's lung. Malt worker's lung, one of the best known of these, is an occupational mycosis encountered during beer manufacture correlated with inhalation of high concentrations of
Aspergillus clavatus and
A. fumigatus spores from contaminated barley.
Adapted from
An Overview of the Genus Aspergillus by
Joan W. Bennett writing in
Aspergillus: Molecular Biology and GenomicsFurther readingLabels: Aspergillus Allergies, Aspergillus Asthma