Abstract

House dust mites can be found in beds, carpets and soft furnishings. They primarily feed on human skin scales and are normally invisible to the naked eye due to their size (less than 1 mm) and their translucency. Since HDM thrive in warm and humid environments, their infestations are linked to climatic characteristics and indoor conditions. Exposure to HDM allergens can lead to allergic sensitization and to exacerbation of rhinitis, eczema and asthma symptoms. Noticeable differences have been found in the prevalences of allergic sensitization and asthma symptoms worldwide, with the UK having some of the highest values (ISAAC Steering Committee, 1998). Several epidemiological studies have reported an increase in the occurrence of allergies and asthma over the past 30-40 years, particularly in affluent countries. Some authors even refer to an “epidemic” of allergy and asthma (Holgate, 2004), although there is some evidence that this “epidemic” may have reached a plateau in certain countries, including the UK (Anderson et al, 2004). Some authors have also that the rise in asthma levels in Westernized countries may be due to recent changes in the building stock, whereby energy efficiency concerns may have contributed to excessively low ventilation rates in housing, resulting in favourable conditions for HDM infestations because of high moisture levels (Howieson et al, 2003). However, most existing data is inadequate for definitive conclusions to be drawn on whether low ventilation rates directly cause ill-health (Davies et al, 2004). Although it is unlikely that increased exposure to perennial allergens (such as dust mite allergens) is the sole cause of the allergy and asthma “epidemic”, these allergens do play a role in explaining, for example, the worldwide variations in allergies and asthma – which partly reflect differences in exposure to HDM allergens due to geographic variations in climatic conditions.