Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
studies collect vacuum samples using a protocol that, at least
internally, standardizes equipment, area, duration and location. Mites
are typically found in higher concentration in bedding. Typical areas
would include mattresses, pillows, blankets and bedroom floors.
Because of spatial variability, mixed floor samples can be used. Other
areas of high use include living room, upholstered chairs and couches,
and covered floors. Bischoff et al. (1992) describes an approach used
to avoid depletion of the dust reservoir during routine and repeated
sampling.
Mite-antigen levels have been shown to vary with season,
reflecting the moisture and temperature dependency controlling mite
development stages. Garrett (1996) conducted a yearlong study in 80
homes in eastern Australia. Fig. 26 reveals the temporal variation in
Der p I, the prominent allergen. The allergen levels in dust collected
from the bedroom and living room are higher during the warmer and more
humid months of the year. Garrett (1996) has shown that the allergen
level for Der p I is consistently higher in dust collected directly
from the bedding. The between-home variation is quite apparent,
ranging over almost two orders of magnitude. Examining Fig. 27 offers
an explanation for the higher levels of greater variability in the
allergen levels recovered from the bedding dust. Mites survive better
in mattresses with spring cones than in foam rubber. Presumably, less
moisture is retained in the hydrophobic foam material. Also, wool
sheets and blankets favour the growth and retention of mite antigens
more than alternative bedding material. Other studies on mites in wool
rugs suggest that the thermal properties of wool help mites to survive
fluctuations in temperature and moisture and, perhaps, inhibit their
removal.
9.3 Allergens from pets and cockroaches
For estimating the exposure to allergens derived from pets (e.g.,
cats and dogs), and cockroaches, the same approaches are available as
for house dust mites and their allergens (i.e., the sampling of air
and dust). The major allergens of the cat (Fel d I), dog (Can f I),
the German cockroach (Bla g I, Bla g II), and the American cockroach
(Per a I), have been characterized and purified (Chapman et al., 1988;
Pollart et al., 1991a; Schou et al., 1991, 1992). Research is still in
progress to further unravel the structure of the allergens derived
from pets and roaches (and house dust mites) using techniques for
allergen cloning and sequencing.
9.3.1 Air sampling for allergens from pets and cockroaches
Cockroaches are year-round inhabitants of homes. They need access
to both food and water, so they are often found in kitchens and
bathrooms. Unlike mites, where the antigen source is in faecal matter,
cockroaches are thought to secrete their allergen on to their bodies
and on to surfaces (Vailes et al., 1990). This means that body parts,
egg shells, faecal particles and saliva might contain allergens
(Lehrer et al., 1991).
Similarly, a wide range of materials derived from mammals contain
potentially allergenic material, including hair, dander, serum,
saliva, urine and faecal matter. Direct contact as well as inhalation
and ingestion can cause allergic reactions (Burge, 1995). Because of
the popularity of cats and dogs as domestic pets, they have been the
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