Schistosoma mansoni infection is associated with a reduced course of asthma

Background: Helminthic infections decrease skin reactivity to indoor allergens, but data on whether they influence asthma severity are lacking. Objective: This study evaluated the course of asthma in patients with and without Schistosoma mansoni infection. Methods: Asthmatic subjects were enrolled from 3 low-socioeconomic areas: a rural area endemic for schistosomiasis (group 1) in addition to a rural area (group 2) and a slum area (group 3), both of which were not endemic for schistosomiasis. A questionnaire on the basis of the International Study of Asthma and Allergies in Childhood study was applied in these 3 areas, and from each area, 21 age- and sex-matched asthmatic subjects were selected for a prospective 1-year study. Pulmonary function tests, skin prick tests with indoor allergens, stool examinations, and serum evaluations were performed in these subjects. Every 3 months, the subjects were evaluated for asthma exacerbation through physical examination, and a questionnaire regarding asthma symptoms and use of antiasthma medicine was administered. Results: The prevalence of S mansoni infection was greater in group I compared with in groups 2 and 3 (P < .0001), whereas the frequency of other helminth and protozoa infections was similar among the 3 groups. The frequency of positive skin test responses to indoor allergens was less (19.0%) in group I subjects relative to those in group 2 (76.2%) and group 3 (57.1%; P < .001). The frequencies of symptoms, use of antiasthma drugs, and pulmonary abnormal findings at physical examination were less in group 1 subjects than in group 2 and 3 subjects (P = .0001). Conclusion: Our results suggest that S mansoni infection is associated with a milder course of asthma.