What are the determinants of mold allergy?

Updated: Dec 02, 2020
  • Author: Shih-Wen Huang, MD; Chief Editor: Harumi Jyonouchi, MD  more...
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The cross-reactivity (shared epitopes) of allergens derived from common airborne fungus spores remains controversial. Allergenic cross-reactivity such as observed between Phoma and Alternaria extracts more likely reflect the presence of shared epitopes in the species' reproductive stages. Establishing biologic or allergenic properties among molds is difficult, especially imperfect fungi. Therefore, defining Ag determinants is important when a mold allergen extract is prepared.

Total airborne fungi in North America range from extremely low levels during periods of below-freezing temperature to peak levels that usually occur in late summer and early autumn. This pattern parallels variations in dominant Cladosporium and Alternaria species in many areas. Penicillium species most often lack a defined annual pattern; A fumigatus may be more prominent from December-April in some areas but can be unpredictable in other regions. Mold allergy may account for persistent respiratory symptoms in individuals during nonpollen seasons.

Fungi readily invade indoor environments, and indoor growth can cause perennial allergic symptoms. Penicillium and Aspergillus species are commonly found in enclosed spaces, followed by Rhizopus and Mucor species. Soiled upholstery and garbage containers are favored sites of indoor fungal growth. The porosity of rubber and synthetic foams and their tendency to remain moist favor fungalgrowth.Basements, window molding, shower curtains, and plumbing fixtures are common sites for indoor fungal growth (see the image below).

Bathrooms are favorite habitats for mold. Bathrooms are favorite habitats for mold.

Poorly maintained cold-mist vaporizers and some console humidifiers can emit dense microbial aerosols during operation. If high relative humidity and condensation persist in indoor environments, mold is likely to recur after decontamination.

The clinical relevance of cross-reactivity among the different fungal species has been largely unknown. However, progress in molecular cloning of fungal allergens and the availability of more than 40 completely sequenced fungal genomes facilitates characterization, cloning, and production of highly pure recombinant allergens; identification of homologous and orthologous allergens; in silico prediction; and experimental in vitro and in vivo verification of cross-reactivity between homologous panallergens. [8] These studies indicate that cross-reactivity is an important component of fungal sensitization.

However, a new study among Swedish children indicated that no association was found between the spore concentration and signs of dampness and moldy odor reported by parents or by professional inspectors. No association was found between the indoor spore concentration and asthma or allergy among children. Thus, one-time air sampling of mold CFU in indoor air is not indicated to identify risk factors for asthma or allergy in children living in Scandinavian countries.

Contradictory to the above study, a population-based study in Montreal children suggests home environmental factors associated with poor asthma control. [4] Of 980 children with active asthma, 36% met criteria of poor control of their diseases. The population's characteristics were related with lack of asthma control, after adjustment, and included children living along high-traffic density streets (PR, 1.35; 95% CI, 1-1.81) and those with their bedroom or residence at the basement level (PR, 1.30; 95% CI, 1.01-1.66). The study concluded suboptimal asthma control appears to be associated with traffic, along with mold and moisture conditions; the latter is a more frequent exposure and, therefore, has a greater public health impact.

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