Bioaerosols - Aerosols: Measurement, Dosimetry, and Health Effects - page 310

Cladosporium herbarum , A. alternata , and Aspergillus fumigatus have been shown to produce a
variety of allergens including several major allergens, that is, Cla h I, Alt a I and II, and Asp f I and
III. Allergens can be found in spores, hyphae, and fungal fragments. At high concentrations fungi
also may be involved in Type III and IV allergic reactions including HP (Section 12.2.2.4). Due to
dificulties with the manufacture and standardization of fungal allergen extracts, commercial assays
are available for only a limited number of indoor fungal allergens (including Alternaria species
allergens) (Section 12.6.4.4). Therefore, exposure data on indoor fungal allergens (as opposed to
fungal spores) are scarce (Section 12.6.2). Other species have been suggested to be related to asthma
in the general population and in workers, but these fungi are not commonly included in allergy tests
and their contribution to fungal allergy is not known. Some studies have shown a higher prevalence
of fungal sensitization in subjects living in damp buildings and in severe asthmatics. Also, in a
large European multi-center study, an association between mold sensitization ( A. alternata and C.
herbarum ) and asthma severity was demonstrated, 232 and allergic responses to molds have been
shown in relation to outdoor exposures to Alternaria species in desert environments. Thus, exposure
to fungal allergens may be related to asthma; however, the evidence that allergic responses play a
major role in asthma development is limited. 78 This may be because mold allergens and IgE directed
against these allergens are very dificult to measure because the natural production of mold allergen
is highly variable. Another possible explanation is that resting spores are less allergenic than spores
that have germinated. 198 Few studies have examined fungal allergy in highly exposed occupational
populations, but speciic IgE to the prevalent species is remarkably absent in some of the studies. 233
The major allergens produced by the house dust mite, Dermatophagoides pteronyssinus (called
Der p 1 and Der p 2) are proteases present in high amounts in fecal pellets, which contain digestive
enzymes and partially digested food (primarily human skin lakes). 77,234 Another house dust mite
species, Dermatophagoides farinae produces Der f 1 as its major allergen. Elevated levels of these
allergens have been detected in house dust, mattress dust, and bedding collected in damp homes.
The major cat ( Felis domesticus ) and dog ( Canis familiaris ) allergens are proteins called Fel d 1 and
Can f 1, respectively. These allergens are present in cat and dog dander, saliva, and urine, and can
be found in house dust, dust in other buildings and transportation vehicles, and on clothes of people
that keep pets or are regularly exposed to them. Two major cockroach ( Blatella germanica ) aller-
gens have been identiied called Bla g 1 and Bla g 2, suggested to come from feces or body parts. 77
Indoor allergens such as pet and house dust mite allergens can exacerbate pre-existing asthma
in sensitized subjects, 77 and epidemiological studies have shown an association between indoor
allergen exposure and speciic atopic sensitization (Sections 12.2.2 and 12.2.3). 235 For example,
many studies have shown an association between dust mite allergen levels in house dust and dust
mite speciic sensitization. There also is a strong association between house dust mite sensitiza-
tion and asthma. Moreover, several challenge studies have demonstrated that dust mite allergen
inhalation in allergic asthmatics could produce a strong asthmatic response, and asthma in mite
allergic subjects has been shown to signiicantly improve when they move from high to low expo-
sure areas.
However, few studies have shown a clear association between allergen exposure and new-onset
asthma. 235 From cross-sectional studies, weighted averages of the population attributable risks for
new onset asthma in children has been estimated to be 11% for Fel d 1, 6% for Can f 1, 4% for Der
p 1, and −4% for Bla g 2. 67 Nor have intervention studies minimizing exposure to indoor allergens in
early life proven effective in preventing asthma, 67 and international patterns of asthma prevalence
do not “it” the international patterns of allergen exposure (Sections 12.2.2.1). 98
These observations suggest that different factors may be important in allergy exacerbation than
are involved in new-onset asthma development. Aside from the possibility that indoor allergen
exposure per se is not a major cause of asthma, 67 studies might have suffered from unmeasured or
unknown confounding from other indoor inhalation exposures such as ine particles, ozone, or pro-
inlammatory compounds such as endotoxin or glucan.