Which fungal species cause allergies in humans?

Updated: Dec 02, 2020
  • Author: Shih-Wen Huang, MD; Chief Editor: Harumi Jyonouchi, MD  more...
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Several fungal species (usually molds) cause allergic reactions in humans. The most common and best described mold allergen sources belong to the taxonomic group fungi imperfecti (usually asexual stages of Ascomycetes), which includes Alternaria, Cephalosporium, and Aspergillus species. Species of Basidiomycetes and yeast, such as Candidiasis albicans, are also important allergen sources.

Alternaria and Cladosporium species are common in outdoor environments worldwide. Airborne spores and mycelium debris of Cladosporium and Alternaria species are present during spring, summer, and especially autumn because of the degradation of leaves and other biomaterial. In indoor environments, Aspergillus and Penicillium species predominate with relatively few characteristic seasonal changes.

In early 1970, the United States faced an unexpected energy crisis because of the political climate in the world. The heavy dependence on foreign oil suddenly became a national issue. In responding to the call for conservation, the housing industry used more energy-saving insulation in buildings. However, the heavy insulation unexpectedly resulted in an excessive increase of humidity inside those buildings. This led to increase in mold-related health issues because the increased humidity led to higher mold counts within the buildings.

Similarities of allergen epitopes (antigenic [Ag] determinants) have been reported among some mold species, as observed in the closely related genera Alternaria and Stemphyllium. Otherwise, no immunochemical similarities have been detected among the major allergens of these species. The preparation of allergen extracts from cultured mold is very difficult secondary to low protein and high carbohydrate contents and the presence of potent proteolytic enzymes.

The Pollution and the Young (PATY) study included more than 58,000 children. [1] The study was conducted in Russia, North America, and 10 countries in Western Europe. The children were aged 6-12 years. The investigators studied the association between visible molds reported in the household and a spectrum of 8 respiratory and allergic symptoms within each study. Positive association between exposure to mold and children's respiratory symptoms were consistently noted across studies and across outcomes. For instance odds ratios ranged from 1.3 (95% confidence interval [CI], 1.22-1.39) for nocturnal cough to 1.5 (95% CI, 1.31-1.73) for morning cough.

A study in Finland showed the most common mold to induce occupational rhinitis was A fumigatus. [2] Association between the immunoglobulin E (IgE) sensitization and exposure level was statistically significant. The mold that grew in conjunction with moisture damage was the leading cause of occupational rhinitis.

A study indicated that IgE sensitization of fungi mirrors fungal phylogenetic systematics. [3] A database was compiled from recorded serum IgE antibody levels in response to 17 different fungal species from 668 individuals sensitized to at least one of the 17 species. By applying a cluster method to this data set, the fungal species were grouped into a hierarchical organization. The resulting organization was compared with published fungi findings. The results of this study showed that the hierarchical structure of fungi based in IgE antibodies in sensitized individuals reflected the phylogenetic relationship. Examples include the distinct separation of basal fungi from the subkingdom Dikarya, as well as individual cluster formations of fungi belonging to the subphylum Saccharomycotina and order Pleosporales.

This is the first study that demonstrates a close relationship between molecular fungal systematics and IgE sensitization to fungal species. Because close evolutionary organisms typically have a higher degree of protein similarity, IgE cross reactivity is likely the main reason for obtained organization.

Culturable molds in indoor air and the association with moisture-related problems and asthma and allergy among Swedish children has been reported. [3] Although mold spore exposure indoors has been suggested as a possible explanation for airway problems such as asthma and allergy among people living in buildings with moisture-related problems, this study could not find any associations between the spore concentrations in indoor air and signs of dampness and moldy odor reported by parents or observed by professional inspectors.

No association between the indoor spore concentration and asthma or allergy among children was noted. With these results, the authors concluded that one-time air sampling of mold colony-forming unit (CFU) in indoor air was not indicated to identify risk factors for asthma or allergy in children living in Scandinavian countries.

In contrast, in a study of environmental factors associated with poor asthma control in Montreal, suboptimal asthma appeared to be mostly associated with traffic, along with mold and moisture conditions. [4] The mold and moisture control thus have a greater public health impact.

In another European study, authors reviewed the projection of the effects of climate change on allergic asthma, in particular the contribution of aerobiology. [5] The authors believe climate change is unequivocal and reprensts a possible threat for patients affected by allergic conditions. However, they acknowledged numerous limitations that make prediction uncertain. More stress on pollen and spore exposure in the diagnosis and treatment guidelines of respiratory and allergic diseases are recommended. Collection of aerobiological data in a structured way at the European level and support of multidisciplinary research teams in this area was highly emphasized.

In one study in the United Kingdom in the asthmatic patients, it was shown that Aspergillus fumigates detection in sputum is associated with A fumigates -IgE sensitization, neutrophilic airway inflammation, and reduced lung function compared to asthmatics with IgG sensitization or asthmatics without sensitization to A fumigatus. This supports the concept that allergic inflammation could significantly lead to fixed airway obstruction in asthma, as illustrated with effect of airway colonization and sensitivity with A fumigatus. [6]

One of the problems with mold exposure estimates is the lack of quantitative, standardized methods for describing the residential mold burden. A metric called the Environmental Relative Moldiness Index (ERMI) has recently been developed and validated in a national survey of homes. [7] . A DNA-based, mold-specific quantitative polymerase chain reaction of 26 species formed the basis of the ERMI. The ERMI scale usually ranges from approximately -10 to 20 and is divided into quartiles, with the highest-quartile homes (ERMI value >5) having the highest mold burden. [7]  

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