Microbial agents, allergens and atopic diseases - contributions to the PARSIFAL study

Over the past decades, the prevalence of allergic diseases in childhood has increased considerably, especially in many western industrialized countries. The rising prevalence might be due to changes in allergen exposure, early infections and/or lifestyle factors. The PARSIFAL (Prevention of Allergy - Risk factors for Sensitization In children related to Farming and Anthroposophic Lifestyle) project focused on two groups of children who have shown a relatively low prevalence of atopic diseases and sensitization: farm children and children of families with an anthroposophic lifestyle. Contact with farm animals has been associated with a decrease in the risk of atopic disease, which might be due to exposure to microbial compounds. The anthroposophic way of life involves several characteristics, such as restrictive use of antibiotics, antipyretics and vaccinations, as well as certain dietary habits, which might be negatively associated with atopic diseases. Main objectives of the PARSIFAL study were 1) to investigate whether differences in atopic disease prevalences between farm children or children from anthroposophic families and respective references, as observed previously, could be confirmed in a large population of children from 5 European countries and 2) to explore factors which might explain the lower prevalence of atopic diseases in these children. The work in this thesis specifically focused on the role of allergens and microbial agents in house dust. Taking together the results of this thesis, it can be concluded that microbial agent levels in house dust may partly account for the protective effect of living on a farm to atopy and/or wheeze. The protective effect of an anthroposophic lifestyle, as observed in some countries but not in others, could not be explained by microbial agent levels. The relatively low prevalence of atopic diseases in these groups of children could not be attributed to lower pet or mite allergen levels. Higher pet allergen levels, as observed in the homes of these children, could be related to the lower prevalence of atopic diseases, but this seems unlikely in view of conflicting literature on this topic