Dust mites multiply in a damp environment
From
the World Health Organization in its report WHO Guidelines for Indoor
Air Quality: Dampness and Mould, published July 16, 2009
[There is a]
close association between damp indoor environments and dust mites. The
reader is referred to the report of the Institute of Medicine (2000) on
house dampness and asthma for a more detailed overview of the literature on
the associations between indoor damp, house dust mite allergens and asthma.
House dust mites are arachnids, and many different species have
been identified; however, only a few are of
concern with respect to damp indoor environments. The natural food source of
house-dust mites includes skin scales, although many other sources may be
used.
Therefore, in most houses, dust mite nutrition is abundantly available,
particularly in mattresses and carpets or rugs. Laboratory studies have
shown that most dust mites require a relative humidity in excess of 45–50%
for survival and development, but they feed and multiply more rapidly at
higher relative humidity (Arlian, 1992). Indoor humidity is therefore the
main influence on the presence and propagation of house dust mites, as
confirmed in several field studies (van Strien et al., 1994; de Andrade et
al., 1995; Simpson et al., 2002; van Strien et al., 2004; Zock et al.,
2006). Damp houses therefore significantly increase exposure to dust-mite
allergens, at least in populations living in mild and temperate climates.
Dust mites produce the
predominant inhalation allergens in many parts of the world. The most common
mite species that produce allergens are
Dermatophagoides pteronyssinus
and
Dermatophagoides farinae.
The major allergens produced by
D. pteronyssisus
(called Der p I and Der p II) are proteases, which are present in large
amounts in faecal pellets (Institute of Medicine, 2000). The major allergen
produced by D. farinae
is Der f I. Elevated levels
of these allergens have been detected in house dust, mattress dust and
bedding in damp houses (van Strien et al., 1994; Simpson et al., 2002; van
Strien et al., 2004). As the focus of these guidelines is indoor dampness
and microorganisms, dust mite allergen levels are not discussed further.
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