Environmental and Occupational Disorders
Reduced risk of atopy among school-age children infected with geohelminth parasites in a rural area of the tropics,☆☆

https://doi.org/10.1067/mai.2003.1348Get rights and content

Abstract

Background: Childhood infections might protect against the expression of atopy. Geohelminths are among the most prevalent infections of childhood and might contribute to the low prevalence of allergic disease reported from rural areas of the tropics. Objective: We sought to establish whether geohelminth infections protect against atopy and to explore whether this protection is dependent on infection chronicity. Methods: The risk of atopy (measured by means of allergen skin test reactivity) associated with active geohelminth infections (measured by means of the presence of eggs in stool samples) or with chronic geohelminth infections (measured by means of high levels [≥3564 IU/mL] of total serum IgE or the presence of detectable anti-Ascaris lumbricoides IgG4 antibodies) was investigated in an analytic cross-sectional study conducted among school-age children attending rural schools in Pichincha Province in Ecuador. Results: A total of 2865 children aged 5 to 19 years from 55 schools was examined. Active infection with any geohelminth and infections with A lumbricoides or Ancylostoma duodenale were associated with significant protective effects against allergen skin test reactivity. Children with the highest levels of total IgE or with anti-A lumbricoides IgG4 antibodies were protected against skin test reactivity also, and the protective effects of high IgE or anti-A lumbricoides IgG4 and or active geohelminth infections were statistically independent. Conclusion: Active infections with geohelminth parasites and the presence of serologic markers of chronic infections (high levels of total serum IgE or anti-A lumbricoides IgG4) are independent protective factors against allergen skin test reactivity among school-age children living in an endemic region of the rural tropics. (J Allergy Clin Immunol 2003;111:995-1000.)

Section snippets

Study population

The study area covered schools (for children aged 5-19 years) in the Districts of Pedro Vicente Maldonado, Puerto Quito, and Los Bancos in Pichincha Province. The area is a subtropical-tropical rain forest at altitudes of 200 to 1100 meters above sea level. All 55 schools included in the study served rural communities that ranged in size from approximately 100 to 3000 individuals. All children attending the schools were eligible to participate. Informed verbal consent was obtained from the

Results

Stool and skin test examinations were performed on samples from 2865 (88.2%) subjects of a total eligible school population of 3249 attending 55 schools. The main reason for nonparticipation was failure to provide a stool sample (366 [95.3%] of 384 nonparticipants). There were only slight differences in the mean age (10.3 vs 10.6 years), sex distribution (boys 46.9% vs girls 52.5%), prevalence of recent anthelmintic treatment (63.4% vs 63.6%), and prevalence of atopy (21.9% vs 22.4%) between

Discussion

The results of our cross-sectional study indicate that current infections with geohelminths are protective against allergen skin test reactivity. To our knowledge, this is the first large study to show a protective effect among school-age children living in an endemic rural area. A strong protective effect was observed for the presence of any of the 3 locally endemic geohelminth parasites (A lumbricoides , T trichiura , and A duodenale ) after controlling for the effects of age, sex, recent

Acknowledgements

We thank David Gaus, Carlos Burneo, and Carlos Sandoval for help in choosing the field site and setting up a field laboratory, for facilitating approval of the study through local Ministry of Health offices, and for their long-term collaborative support through the foundation Salud y Desarollo Andino (SALUDESA). We also thank Martin Chapman for his helpful advice and assistance at the start of the study and Ms Brenda Rae Marshall for help in preparing this manuscript.

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Supported in part by the Wellcome Trust.

☆☆

Reprint requests: Thomas B. Nutman, MD, LPD, NIAID, 4 Center Drive, Room 4/126, NIH, Bethesda, MD 20892.

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