subjects exposed to rust and dark-spored imperfecti fungi was described more tha

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Mold Allergy

Last Updated: October 11, 2004 Rate this Article

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http://www.emedicine.com/ped/topic1471.htm

Synonyms and related keywords: fungal allergy, fungi, Oomycetes,

Zygomycetes, Ascomycetes, Basidiomycetes, Deuteromycetes, allergic

rhinitis, allergic conjunctivitis, allergic asthma, immunoglobulin E–

mediated asthma, IgE-mediated asthma, AFS, allergic fungal

sinusitis, ABPA, allergic bronchopulmonary aspergillosis, ABPM, non-

Aspergillus allergic bronchopulmonary mycosis, non-Aspergillus ABPM,

EAA, extrinsic allergic alveolitis, wood pulp worker's lung, malt

worker's lung, farmer's lung , maple bark stripper's lung, sewage

worker's lung, paprika splitter's lung, humidifier lung, ventilation

pneumonitis

Author: Shih-Wen Huang, MD, Medical Director of Allergy Service,

Professor, Department of Pediatrics, Division of Immunology and

Infectious Diseases, University of Florida College of Medicine

Shih-Wen Huang, MD, is a member of the following medical societies:

American Academy of Allergy Asthma and Immunology

Editor(s): C Lucy Park, MD, Director, Allergy and Asthma Center,

Associate Professor, Department of Pediatrics, University of

Illinois at Chicago; L Windle, PharmD, Adjunct Assistant

Professor, University of Nebraska Medical Center College of

Pharmacy, Pharmacy Editor, eMedicine.com, Inc; J Valacer, MD,

Consulting Staff, Hoffman La Roche Pharmaceuticals; Pallares,

MD, Clinical Assistant Professor, Department of Pediatrics, Division

of Allergy and Immunology, University of Louisville; and Mark

Ballow, MD, Chief, Division of Allergy and Immunology, Buffalo

Children's Hospital; Professor, Department of Pediatrics, State

University of New York at Buffalo

Disclosure INTRODUCTION Section 2 of 10

Author Information Introduction Clinical Differentials Workup

Treatment Medication Follow-up Miscellaneous Bibliography

Background: 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 can occur in

persons of various ages.

Fungi as aeroallergens

Airborne spores and other fungi particles are ubiquitous in nonpolar

landscapes, especially among field crops, and often form the bulk of

suspended biogenic debris. The term mold is often 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 sensitization to diverse fungi is now recognized. Since

fungus particles are commonly derived from wholly microscopic

sources, exposure hazards are assessed largely through direct

sampling of a suspect atmosphere. Because of small size, fungal

emanations present special collection requirements to ensure

particle viability for culture-based studies.

Functional biology of fungi

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.

In considering known and potential allergens, 5 major classes of

fungi have particular clinical significance: Oomycetes, Zygomycetes,

Ascomycetes, Basidiomycetes, and Deuteromycetes.

Most molds require elemental oxygen during growth. Traces of formed

carbohydrate are also essential. Vegetative hyphae of most fungi

grow best between 18° and 32°C, and, although most become dormant at

subfreezing temperatures, a few may sporulate below 0°C. At the

other extreme, although 71°C is generally lethal for molds, certain

types thrive at slightly cooler temperatures. Aspergillus fumigatus

and Aspergillus niger tolerate a wide range of temperatures.

Atmospheric moisture not only affects the growth and fruiting of

fungi but also spore dispersion and resultant prevalence. Spore

counts typically rise with rainfall, fog, and damp, nocturnal

conditions. Rain and dew splash also foster dispersion of slime

spores. As a result, atmospheric recoveries of Fusarium, Phoma,

Cephalosporium, and Trichoderma species peak with rainfall.

The reproductive units of many fungi are detached by direct wind

scouring or wind-induced substrate motion. Such dry spore dispersal

increases as airspeed rises and relative humidity falls, peaking

often during summer afternoons. At such time, typical spores of

Cladosporium, Alternaria, Epicoccum, Helminthosporium, Rhizopus,

Aspergillus, and Penicillium species also may peak. The circadian

trends in changes of temperature, humidity, airspeed, and light

intensity frequently interact to promote diurnal airborne spore

levels. All data emphasize that regional vegetation strongly affects

the local airborne spore levels.

Assessing the prevalence of fungi in air

Studies of airborne fungi provide prevalence data that are important

to estimate patients' exposures to molds. A common method of

sampling molds is to use an air sample volumetric

collector. The collector machine is allowed to sample the designated

space for 5 minutes, trapping air particles in the filter. The

filter then is placed on a Petri dish with media containing

Sabouraud glucose, potato dextrose, and malt extract agar. Colonies

grow on the agar plate, where an experienced mycologist often can

identify the species based on gross appearance. Spore counts may be

expressed as the number of colonies from a cubic meter of air. If

the counts are higher than 200 spores in a cubic meter of air,

allergic patients are more likely to manifest symptoms.

Clinical relevance of allergenic fungi

Several fungal species (usually molds) have been shown to cause

allergic reactions. The most common and best-described mold allergen

sources belong to the taxonomic group Fungi Imperfecti (usually

asexual stages of Ascomycetes) with Alternaria, Cephalosporium, and

Aspergillus species. Species of Basidiomycetes and yeast such as

Candida 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 due to the degradation of leaves and

other biomaterial. In indoor environments, Aspergillus and

Penicillium species predominate with less characteristic seasonal

changes; this fact has become more apparent since the early 1970s as

the housing industry has installed more energy-saving insulation in

homes.

Allergen similarities 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. Mold cultures (whether

mycelium with spores or pure spores), low amounts of protein, high

amounts of carbohydrate, and active proteolytic enzymes make the

preparation of allergen extracts from cultured mold difficult.

Pathophysiology:

Immunologic evolution of allergy

Allergic diseases are mediated by antigen-specific immunoglobulin E

(IgE) produced by host B lymphocytes. The allergic immune response

begins with the processing of mold antigens by host dendritic cells.

The helper-cell subset of T lymphocytes (TH2) interacts with

dendritic cells and results in excessive production of interleukin

(IL)–4. B cells respond by producing IgE. When IgE binds to IgE-

specific cell surface receptors on mast cells in tissue, mast cells

are activated and release a variety of preformed and newly produced

mediators including histamine, leukotrienes, and prostaglandins.

Simultaneously, a variety of chemotactic factors, such as

leukotriene B4, platelet activating factor, and eosinophil

chemotactic factor, induce an influx of eosinophils, neutrophils,

and mononuclear cells into the site of mast cell activation.

The eosinophil population increases by clonal expansion caused by IL-

3 and IL-5. Thus, IgE-mediated reactions result in inflammatory

diseases. The initial inflammatory process initiated by mold allergy

may be further compounded by the waves of inflammatory cell

infiltration producing different clinical disorders in the upper or

lower respiratory tract that can vary in persons of different ages.

Allergic disorders are driven primarily by the TH2 response, but a

TH1 response characterized by cell-mediated immunity may also

contribute to adverse reactions to mold. The known clinical

disorders related to adverse immune reactions to molds are listed in

Clinical forms of mold allergy.

Mold-induced respiratory symptoms may be notably delayed and may be

associated with bacterial superinfection. This may reflect the

concomitant microbial agents (and endotoxin) present in wild sources

of mold growth, such as dusts from decomposing plant material, which

may compound clinical manifestations.............

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