High allergic reactivity in a tropical environment.

The prevalence of atopic disease in tropical populations is often considered to be low, and this has been attributed to an immunological modulating effect of intestinal helminthiasis. We, however, report that the frequency of positive allergic history and skin-test reactivity to groups of major environmental allergens is extremely high (43 and 63% respectively) in children in Caracas, Venezuela (Lat. 10 degrees N). These values were statistically significantly greater than in a group of children with a similar age and sex distribution studied in parallel, but having limited or no contact with a tropical environment (29 and 37% respectively). The two groups differed with respect to the sporadic and light intestinal helminthic infections (such as ascariasis) experienced by the Venezuelans, compared to rare contact in the 'non-tropical' group. This was probably the cause of the increased total serum IgE levels of the former children (369 vs 68 iu/ml), and possibly, therefore, their higher allergic reactivity.