Interactions among climate change, air pollutants, and aeroallergens

Introduction Although both genetic and environmental factors are important in explaining the large variations in asthma within and between populations (Asher et al., 1995), environmental factors are likely to offer the greatest opportunities for change. We have learned from past and ongoing studies of exposures in the urban environment (and more recently the suburban and rural environments) that environmental factors are inextricably combined with social factors (e.g., poverty, substandard housing) which we do not completely understand (Chew et al., 2006a; Gold and Acevedo-Garcia, 2005; Gruchalla et al., 2005; Kitch et al., 2000; Lin et al., 2012; Matsui et al., 2003, 2004; Perry et al., 2012; Phipatanakul et al., 2005). As such, it is difficult to definitively attribute an increased burden of allergy to climate change. However, it appears that climate change-related factors (both direct and indirect) could be associated with a changing profile of indoor allergens and in some cases either an increase or a decrease in indoor allergen concentrations in buildings, most notably the home environment. Dust Mite Allergens Dust mite allergen is one of the most ubiquitous indoor allergens known (Platts-Mills et al., 1997). Much of the allergenicity attributed to dust mites is due to their faecal pellets, measuring from 10-40 µm in diameter (Tovey et al., 1981). Dust mites are microscopic and feed on human skin scales, fungi, and other forms of organic matter (Colloff, 2009; Gravesen, 1978). Dust mites are very sensitive to relative humidity (RH), with greatest survival between 70% and 85% RH (Arlian, 1975; Colloff, 2009). When humidity falls below ~50%, dust mites die because their only mechanism for water intake is via their exoskeleton, so they become severely dehydrated. Temperate and tropical areas differ in the distribution of dust mite taxonomic groups (i.e., taxa), and there can also be differences in patterns of sensitisation to their allergens among allergic individuals living in those areas. For example, the most abundant mite species recovered in house dust from Puerto Rico in studies to date has been Dermatophagoides pteronyssinus, followed by Blomia tropicalis and D. farinae, among other taxa (Montealegre et al., 1997a). These findings contrast with those from more temperate climates, where allergens from D. farinae are more frequently recovered (Chew et al., 1998; Rose et al., 1996; Wood et al., 1988).