The Biodiversity Hypothesis and Allergic Disease
Biodiversity loss and climate change secondary to human activities are increasingly being associated with adverse health effects. A recent position statement of the World Allergy Organization discusses the effects of biodiversity loss on environmental and commensal (indigenous) microbiotas. (1) The authors describe, that metagenomic and other studies of healthy and diseased individuals reveal that reduced biodiversity and alterations in the composition of the gut and skin microbiota are associated with various inflammatory conditions, including asthma, allergic and inflammatory bowel diseases (IBD), type-1 diabetes, and obesity. Altered indigenous microbiota and the general microbial deprivation characterizing the lifestyle of urban people in affluent countries appear to be risk factors for immune dysregulation and impaired tolerance. The risk is further enhanced by physical inactivity and a western diet poor in fresh fruit and vegetables, which may act in synergy with dysbiosis of the gut flora. Studies of immigrants moving from non-affluent to affluent regions indicate that tolerance mechanisms can rapidly become impaired in microbe-poor environments. The authors evaluate the data on microbial deprivation and immune dysfunction as they relate to biodiversity loss and propose that biodiversity, the variability among living organisms from all sources are closely related, at both the macro- and micro-levels. Loss of the macrodiversity is associated with shrinking of the microdiversity, which is associated with alterations of the indigenous microbiota. Data on behavioural means to induce tolerance are outlined and a proposal made for a Global Allergy Plan to prevent and reduce the global allergy burden for affected individuals and the societies in which they live.
A second, more clinical review paper provides suggestions to help the physicians integrate recommendations about improvements in outdoor and indoor air quality and the likely response to predicted alterations in the earth's environment into their patient's treatment plan. (3) Examples of responses to climate change including energy reduction retrofits in homes that could potentially affect exposure to allergens and irritants, more hot sunny days that increase ozone-related difficulties, and rises in sea level or altered rainfall patterns that increase exposure to damp indoor environments are reviewed. Climate changes can also affect ecosystems, manifested as the appearance of stinging and biting arthropods in new areas. Higher ambient carbon dioxide concentrations, warmer temperatures, and changes in floristic zones could potentially increase exposure to ragweed and other outdoor allergens, whereas green practices such as composting can increase allergen and irritant exposure. Finally, increased energy costs may result in urban crowding and human source pollution, leading to changes in patterns of infectious respiratory illnesses. Improved governmental controls on airborne pollutants could lead to cleaner air and reduced respiratory diseases but will meet strong opposition because of their effect on business productivity. The authors conclude that the allergy community must therefore adapt to these changes.
1.Haahtela T, Holgate S, Pawankar R, Akdis CA, Benjaponpitak S, Caraballo L, Demain J, Portnoy J, von Hertzen L; WAO Special Committee on Climate Change and Biodiversity. The biodiversity hypothesis and allergic disease: world allergy organization position statement.World Allergy Organ J. 2013 Jan 31;6(1):3. doi: 10.1186/1939-4551-6-3.
2.Hanski I, von Hertzen L, Fyhrquist N, Koskinen K, Torppa K, Laatikainen T, Karisola P, Auvinen P, Paulin L, Mäkelä MJ, Vartiainen E, Kosunen TU, Alenius H, Haahtela T. Environmental biodiversity, human microbiota, and allergy are interrelated. Proc Natl Acad Sci U S A. 2012 May 22;109(21):8334-9. doi: 10.1073/pnas.1205624109. Epub 2012 May 7.
3.Barnes CS, Alexis NE, Bernstein JA, Cohn JR, Demain JG, Horner E, Levetin E, Nel A, Phipatanakul W. Climate Change and Our Environment: The Effect on Respiratory and Allergic Disease. J Allergy Clin Immunol Pract. 2013 Mar;1(2):137-141.