Independent effects of intestinal parasites infection and domestic allergen exposure on risk of wheeze in Ethiopia: a nested case-control study

Background Why asthma is rare in rural subsistence societies is not clear. We tested the hypotheses that the risk of asthma is reduced by intestinal p arasites or hepatitis A infection, and increased by exposure to dust-mite a llergen or organophosphorus insecticides in urban and rural areas of Jimma, Ethiopia. Methods From 12876 individuals who took part in a study of asthma and atopy in urban and rural Jimma in 1996, we identified all who reported wheeze in the previous 12 months, and a random subsample of controls. In 1999, we as sessed parasites in faecal samples, Der p 1 levels in bedding, hepatitis A antibodies, serum cholinesterase (a marker of organophosphorus exposure), t otal and specific serum IgE, and skin sensitisation to Dermatophagoides pte ronyssinus in 205 cases and 399 controls aged over 16 years. The effects of parasitosis, Der p 1 level, hepatitis A seropositivity, and cholinesterase concentration on risk of wheeze, and the role of IgE and skin sensitisatio n in these associations, were analysed by multiple logistic regression. Findings The risk of wheeze was independently reduced by hookworm infection by an odds ratio of 0.48 (95% CI 0.24-0.93, p=0.03), increased in relation to Der p 1 level (odds ratio per quartile 1.26 [1.00-1.59], p=0.05), and w as unrelated to hepatitis A seropositivity or cholinesterase concentration. In the urban population, D pteronyssinus skin sensitisation was more stron gly related to wheeze (9.45 [5.03-17.75]) than in the rural areas (1.95 [0. 58-6.61], p for interaction=0.017), where D pteronyssinus sensitisation was common, but unrelated to wheeze in the presence of high-intensity parasite infection. Interpretation High degrees of parasite infection might prevent asthma symp toms in atopic individuals.