Avaliação da associação entre respostas alérgicas e infecção por Schistosoma mansoni em indivíduos com baixa carga parasitária residentes no Distrito Rural de Brejo do Amparo, em Januária MG

Abstract

Allergic diseases and infections caused by helminth induces an immune response predominantly Type 2, stimulating the increase and activation of eosinophils, basophils, mast cells and high levels of IgE circulating. In the case of schistosomiasis, the Th2 response is stimulated with the beginning of oviposition and is usually followed by an increase in IL-10, resulting in a modulated chronic infection that persists for years. Some epidemiological studies have reported inverse associations between allergy and helminths, suggesting that frequent exposure of the immune system to infection can lead to development of a modulated immune response, avoiding, in part, development of inflammatory diseases. However, most studies have been conducted in areas with high parasitic load, a situation that has been changed in many Brazilian endemic areas in recent years due to the impact of control programs. In order to clarify some of these aspects, the present cross-sectional study aims to establish possible relationship between helminth infections and allergic reactions in 257 residents in the rural district of Brejo do Amparo, Januária city, State of Minas Gerais. The volunteers of the study answered a socioeconomic questionnaire and other specific questionnaire for identification of allergic diseases (ISAAC), and also provided stool and blood samples to perform the parasitological, immunologic and molecular tests and hemogram. The results showed that the study population have low education and income, and are frequent exposure to sources of parasitic infection. The ISAAC questionnaire identified 38 (17%) individuals with declared and frequent symptoms of asthma, 134 (59%) with rhinitis and 32 (14%) with Eczema. Complementary tests revealed that 23.8% of volunteers had high serum levels of IgE reactive to common allergens in house dust. To ensure the diagnosis of infection in individuals with very low parasitic load, stool samples were examined by several parasitologic techniques (Kato-Katz, Helmintex® and saline gradient) and by PCR-ELISA, showing a prevalence of 54.4% and a median of 4 eggs/g faeces. Serum from each subject was used to determine the total IgE concentration and IL-10 by ELISA. The serum levels of total IgE and number of circulating eosinophils were similar among infected and uninfected subjects, while only 14% presented detectable levels of IL-10 in serum. Multivariate linear regression analysis revealed that S. mansoni-infected individuals with more than 12 OPG had 5 times less chance to develop IgE reactivity against allergen of domestic dust. As established by ISSAC questionnaire in the study population, Asthma was 7 times more frequent in children under 10 years and there was no association between Asthma and IgE reactivity (Atopy), suggesting that the Asthma symptoms was related to viral infections in childhood. Interestingly, Schistosma-infected individuals with more than 12 OPG had 3 times less chance to have Asthma