The order Melanoconoiales is not of allergenic importance. Moniliales
The conidiophores are spread over the entire colony. Moniliales is by far the largest and most diverse order of the Deuteromycetes and contains most of the recognized and suspected fungus allergens. Three families account for most of the fungi that cause allergy in humans: Moniliaceae, Dematiaceae, and Tuberculariaceae.
The Moniliaceae are characterized by colorless or light-colored hyphae and conidia; the colonies are usually white, green, or yellow. The genera Aspergillus (Fig, 6,16), Penicilliumi (Fig.BJZ), Botrytis, Monilia and Trichoderma are "moniliaceous molds" associated with allergic disease.
FIG. 6.16. Aspergillus species. Average spore diameter is 4 pm. The spores are borne in chains and have connecting collars. [Courtesy of Bayer Allergy Products (formerly Hollister-Stier Labs), Spokane, WA.]
FIG. 6.17. Penicillium chrysogenum. Average spore diameter is 2.5 pm. The spores appear in unbranched chains on phialides, the terminal portions of the conidiophores. The phialides and chains of spores resemble a brush. [Courtesy of Bayer Allergy Products (formerly Hollister-Stier Labs), Spokane, WA.]
The family Dematiaceae, one of the most important from the standpoint of allergy, is characterized by the production of dark pigment in the conidia and often in the mycelia. It contains the genera Alternaria (Fig.6.18), Cladosporium (Hormodendrum) (Fig. i 6..19), Helminthosporium (Fig.. 6.20), Stemphyllium (Fig. 6.21.), Nigrosporia, Curvularia, and Aureobasidium (Pullularia). The last is morphologically similar to the yeasts, and is sometimes classified with them and called the "black" yeast. This group often is described as the "dematiaceous molds."
FIG. 6.18. Alternaria alternata. Average spore size is 12 * 33 pm. Spores are snowshoe shaped and contain transverse and longitudinal septae with pores. (Courtesy of Schering Corporation, Kenilworth, NJ.)
FIG. 6.19. Cladosporium species. Average spore size is 4 * 16 pm. Spores occur in chains and have small attaching collars at one end. The first spore buds off from the conidiophore, then the spore itself buds to form a secondary spore. [Courtesy of Bayer Allergy Products (formerly Hollister-Stier Labs), Spokane, WA.]
FIG. 6.20. Helminthosporium species. Average spore size is 15 * 75 mm. The spores, which occur in the ends of the conidiophores, are large, brownish, and have transverse septae. (Courtesy of Schering Corporation, Kenilworth, NJ.)
FIG. 6.21. Stemphyllium species. The spores superficially resemble those of Alternaria but lack the "tail" appendage. Also, they are borne singly rather than in chains. (Courtesy of Schering Corporation, Kenilworth, NJ.)
The Tuberculariaceae produce a sporodochium, a round mass of conidiospores containing macroconidia and microconidia in a slimy substrate. The genera Fusarium (Fig. 6.22) and Epicoccum (Fig.,,,,6.23) are important allergenic fungi in this family.
FIG. 6.22. Fusarium vasinfectum. Average spore size is 4 * 50 pm. The most prevalent spore type is the macrospore, which is sickle shaped and colorless, and contains transverse septae and a point of attachment at one end. [Courtesy of Bayer Allergy Products (formerly Hollister-Stier Labs), Spokane, WA.]
FIG. 6.23. Epicoccum nigrum. Average diameter is 20 pm. Large spores are borne singly on the ends of conidiophores. They are yellowish brown and rough, and develop transverse septae when old. [Courtesy of Bayer Allergy Products (formerly Hollister-Stier Labs), Spokane, WA.]
The family Cryptococcaceae contains the true yeasts, which do not produce hyphae under known cultural or natural circumstances. Allergenic genera within this family include Rhodotorula and Sporobolomyces.
This classification and list of genera are not exhaustive, but do represent most of the important allergenic fungi found in environmental surveys. The fungi listed here are a framework on which an individual allergist can build or make deletions, depending on the region or clinical judgment. Most fungal sensitivity is specific for genus, although species and strain differences have been reported. Where more than one species occurs for a genus, allergenic extracts usually are mixed together, as in "Aspergillus mixture" or "Penicillium mixture." It should be remembered that extracts prepared from fungi are extremely variable in allergenic content and composition.
Certain data concerning the prevalence and ecology of fungi make the list less formidable in practice. With the exception of the Pacific Northwest, Alternaria and Cladosporium (Hormodendrum) are the most numerous genera encountered in most surveys of outdoor air. These fungi are "field fungi" and thrive best on plants in the field and decaying plant parts in the soil. They require a relatively high moisture content (22%-25%) in their substrate. They are mainly seasonal, from spring to late fall, and diminish markedly with the first hard frost. Their spores generally disappear from air samples during the winter months when snow cover is present. Helminthosporium and Fusarium are the other common field fungi. These and certain other fungi propagate in the soil, and their spores are released in large numbers when the soil is tilled.
Aspergillus and Penicillium,, conversely, sometimes are called "storage fungi" because they are common causes of rot in stored grain, fruits, and vegetables. Aspergillus in particular thrives on a substrate with low moisture content (12%-16%). These are the two fungi most commonly cultured from houses, especially from basements, crawl spaces, and bedding. Penicillium is the green "mildew" often seen on articles stored in basements. Rhizopus causes black moldy bread and proliferates in vegetable bins in homes, especially on onions.
The foremost allergenic fungi, based not only on their incidence in atmospheric surveys, but on allergenic skin test reactivity, are Alternaria, Aspergillus, Cladosporium, and Penicillium.. The prevalence of skin test reactivity to fungi in allergic patients is not known but may approach 25% of asthmatics in some surveys (148). Most patients allergic to fungi typically react on skin testing to one or more of these allergens. Many patients also react to other fungi, however, and some to fungi other than these four.
The designations "field" and "storage" fungi or "indoor" and "outdoor" fungi are not precise because exceptions are common in environmental surveys. Moreover, indoor colonization from molds varies with the season, particularly in homes that are not air conditioned ( 149). During the warmer months, Alternaria and Cladosporium spores are commonly found indoors, having gained entry into the home through open windows.
In contrast to field and storage fungi, yeasts require a high sugar content in their substrates, which limits their habitat. Certain leaves, pasture grasses, and flowers exude a sugary fluid that is a carbon source for the nonfermentative yeasts such as Aureobasidium (Pullularia) and Rhodotorula. Hundreds of millions of yeast colonies may be obtained per gram of leaf tissue. Berries and fruit also are commonly colonized. The soil is not a good habitat for yeasts unless it is in the vicinity of fruit trees. Yeasts are often cultured indoors, however.
The relationship of weather to spore dissemination is clinically important, because the symptoms of patients with respiratory allergy are often worse in damp or rainy weather. This has been attributed by some to an increase in the "fungal spore count." Absolute fungal spore counts decrease during and after a rainstorm because some spores, like pollen grains, are washed out or made less buoyant. Most of the common allergenic fungi, such as Aspergillus and Cladosporium, are of the dry spore type, the spores being released by the wind during dry periods. Alternatively, some so-called "wet weather spores," including certain yeasts such as Aureobasidium, Trichoderma, and Phoma and biologically dispersed ascospores, increase. Although these spores are loosened during wet periods and are dispersed by rain droplets, it is unlikely that they are responsible for the mass symptoms that occur during inclement weather. High spore counts are found in clouds and mist, and it is reasonable to attribute some of the symptoms encountered during long periods of high humidity to fungal allergy. Recall that other allergens, such as the house dust mite, also propagate in conditions of high humidity. Snow cover obliterates the outdoor fungal spore count, but the conditions subsequent to thawing predispose to fungal growth and propagation.
The relationship of house plants to indoor fungal exposure has been studied. Contrary to common belief, indoor plantings are associated with only a slight increase in the numbers of spores from such genera as Cladosporium, Penicillium, Alternaria, and Epicoccum. Greenhouses do show an increased number of spores, particularly when plants are agitated by watering or fanning (150). Similar studies in laboratory animal care units fail to show excessive numbers of fungal spores ( 151). Several reviews of fungal sensitivity and the classification of fungi are available ( 107,133,134,152).
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