Letter: IgE, parasites, and allergy

No association found between Strongyloides infestation and asthma

It has been postulated that infestation with Strongyloides stercoralis is associated with asthma. We conducted a case-control study to determine whether the presence of parasites is associated with asthma. We undertook a retrospective analysis of 15,856 stool specimens received by our Parasitology Laboratory from January 1989 to December 1992. The diagnosis of asthma was secured by a chart review or a review of the computer diagnosis coding system. An association between asthma and Strongyloides was tested by calculating an odds ratio, as well as a Fisher's Exact Test to estimate the strength of the relationship. We also prospectively collected stool specimens for Strongyloides in asthmatics hospitalized for acute exacerbations of asthma from January 1992 to January 1993. Of 60 subjects with evidence of Strongyloides in a stool specimen, 6 were asthmatic. Of 203 stool-negative controls matched for age, sex, and ethnicity, 13 were asthmatic (odds ratio, 1:62; 95% confidence interval, 0.6-4.4; Fisher's Exact two-tailed, p = 0.39). Of 443 subjects admitted for acute exacerbations of asthma, stool specimens were analyzed for the presence of Strongyloides from 161, of which two were parasitized. These data suggest no statistically significant difference in prevalence of asthma among patients with Strongyloides infestation compared to those without parasitic infection. These results do not support the hypothesis that there is an association, either causal or protective, between Strongyloides infestation and asthma.

IgE, parasites and asthma in Tanzanian children

Two rural Tanzanian primary schools were surveyed to test the hypothesis that parasitic infestation prevents the development of asthma. 242 pupils were interviewed to determine the prevalence of pupils with recurrent episodes of wheezing. The nineteen pupils so discovered had more exercise-induced bronchial lability than equivalently exercised controls. More girls (12.8%) than boys (3.3%) had asthma. In one school, 77% of the controls had faecal parasites, mainly Ascaris spp., and in the other school 55% of the controls had Schistosoma haematobium in their urine. Parasites were found in similar proportions in the asthmatics. The mean serum IgE for the whole population was 3174 u/ml with no demonstrable difference between the asthmatics and controls. There was no difference in immediate cutaneous hypersensitivity to twenty-two allergens between the asthmatics and controls. These findings suggest that parasitic infestation does not prevent the development of asthma.