The association between helminth infections and atopic diseases

Abstract

Worldwide, allergies are increasingly becoming a public health problem. Several studies have indicated a relation between allergies and a “western” lifestyle. These observations have contributed to the formulation of the hygiene hypothesis, which suggests that low levels of exposure to infections in early childhood increase the risk of developing allergic diseases, which is mainly due to insufficient stimulation of the Th1 immune response. This is in favor of the Th2 response and results in a higher frequency of chronic diseases like allergies, which are characterized by a specific hyperactive Th2 immune response. Helminth infections and allergens both have similar Th2 immune responses. However, it has been noticed that helminth endemic areas are often associated with a lower prevalence of allergic diseases. Therefore, helminth infections are thought to play an important role in the process of allergic disorders, and indicate a relation between helminth infections and allergens. However, studies showed controversial results with both positive and negative associations between helminths and allergens. This indicates a dual or controversial influence of helminth infections on the immune system. Different studies indicate that helminth infections interfere with the predictive value of diagnostic tests for atopy. Generally, atopy is defined by measuring the total level of IgE by the presence of specific IgE for allergens or by the evidence of hypersensitivity by skin prick test (SPT). However, in developing countries, high serum IgE could also indicate chronic helminth infections. Therefore, the use of serum IgE might lead to conflicting results in atopic diagnostics, especially in areas where helminth infections are endemic. In this chapter, the controversial effects of helminth infections on the occurrence of allergies and on the related consequences for atopy diagnostics will be elaborated, with an emphasis on the situations in countries at different stages of economic development.