d1 House dust mite
House dust mites are one of the most common sources of sensitization in all parts of the world. Dermatophagoides pteronyssinus, D. farinae and D. microceras occur in the same areas, but the relative proportions of their distribution vary geographically.
Mites have a life cycle of about 2 to 3 months. The size of the mite is up to 0.3 mm. They live in house dust and thrive in warmth and high humidity. Mites’ faeces seem to be the major source of allergenic exposure. They are about the size of a pollen grain and can therefore very easily become airborne and penetrate the lung alveolus.
Dust, carpets, pillows, mattresses and upholstering furniture containing biological material, especially human dander, are reservoirs of house dust mites. Other sources of exposure are damp houses (>45% relative humidity) or dwellings at low altitudes.
Allergens from mites have both common and speciesspecific determinants. Allergenic determinants are shared with other mites belonging to the Pyroglyphidae family and are highly cross-reactive with other Dermatophagoides species. There seems to be a limited cross-reactivity with storage mites (nonpyroglyphid). Some mite allergenic proteins such as tropomyosin are widely cross-reactive among invertebrates such as shrimps, snails, cockroaches and chironomids.
Studies of house dust allergic individuals around the world have shown that house dust mites are one of the most common causes of symptoms such as perennial type asthma, rhinitis and conjunctivitis, often with nocturnal or early morning episodes.
There is evidence that reduction of mite-allergen levels can cause a major improvement in symptoms of asthma. So far the only effective way to get a permanent reduction of house-dust mite allergens seems to be lowering of the air humidity and temperature together with efficient cleaning.