Toxocara seropositivity, atopy and asthma: a study in Cuban schoolchildren

Introduction: Evidence suggests that human toxocariasis (HT) could stimulate the onset of allergic diseases such as asthma. More specifically, in subjects having a hypothetical 'atopic genotype', HT could boost preexistent allergy symptoms. We tested the latter hypothesis in Cuba, a country where both asthma and HT are prevalent.

Material and methods: In a group of Cuban school-aged children (n = 958), we investigated the association of Toxocara seropositivity and atopic status with asthma. Toxocara seropositivity was diagnosed with ELISA and atopy by allergen skin prick test. Both physician-diagnosed asthma and current wheeze, as determined by International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire, were considered. Associations were assessed using multivariable logistic regression analyses, with either 'physician-diagnosed asthma' or 'current wheeze' as outcome variable.

Results: 40.1% of the children were Toxocara seropositive. Prevalences were 21.7% for current wheeze and 32.7% for physician-diagnosed asthma. The odds of having asthma were almost two times higher in atopic children, but only reached borderline significance (OR=1.90, CI 95%: 0.95-3.80 for physician-diagnosed asthma and OR=1.94, CI 95%: 0.98-3.85 for current wheeze). Toxocara seropositivity and physician-diagnosed asthma were associated (OR=1.51, CI 95%: 1.01-2.26). Moreover, in children without antibodies to Toxocara, being atopic was significantly associated with having physician-diagnosed asthma (OR=2.53, CI 95%: 1.63-3.90), while this association was not present in Toxocara positives (OR=1.38, CI 95%: 0.82-2.37).

Conclusion: Our data confirm previous observations of higher Toxocara seropositivity rates in asthmatic children. Toxocara seropositivity appeared to abrogate the apparent association between atopy and asthma in Cuban children. Although this observation was limited to physician-diagnosed asthma, it challenges the hypothesis that HT stimulates the onset of allergic diseases such as asthma in atopic individuals.