Lack of association between Toxocara canis and multiple sclerosis: A population-based case–control study

According to the hygiene hypothesis, low exposure to pathogens early in life can increase the risk for autoimmune diseases. The hygiene hypothesis has been proposed as a possible explanation for the increased incidence of allergy and autoimmune diseases, including multiple sclerosis (MS), in western countries and an imbalance between Th1 and Th2 responses was proposed as an immunological explanation.1 Helminths have shown a protective effect on the development of experimental allergic encephalomyelitis (EAE) in infected mice, dampening the classical Th1 response through an immunological switch to a Th2 response.2 In order to evaluate the protective role of a Th2 response, we used exposure to Toxocara canis as a surrogate marker. Toxocariasis is one of the most prevalent helminthiases worldwide and is generally asymptomatic. The immunological response of the host is characterized by a Th2 response with the production of a broad range of Th2 cytokines such as interleukin (IL)-4, IL-5, IL-10 and IL-13 that promote the recruitment of eosinophils and the switch in antibody production towards immunoglobulin E (IgE).3 We evaluated the possible protective role of toxocariasis in the development of MS using a population-based case–control study. This study is part of a population-based case–control study conducted in the city of Catania.