When mite allergy mimics helminth sensitization: cross-reactive IgG to Ascaris lumbricoides in a highly atopic child

Sensitization to helminth antigens detected by specific IgE assays may occasionally reflect immunological cross-reactivity rather than true parasitic infection, particularly in highly atopic individuals. A 5-year-old boy was hospitalized for the fourth time because of severe bronchial obstruction and recurrent wheezing. Laboratory findings showed mildly elevated leukocyte count without eosinophilia. Specific IgE testing revealed strong sensitization to house dust mites (Dermatophagoides pteronyssinus and D. farinae, both class 6) and elevated Ascaris lumbricoides–specific IgE (class 4). Stool examination for intestinal parasites was negative. A previous Enterobius vermicularis infestation treated months earlier was reported, with no clinical or laboratory evidence of current or past Ascaris infection. Given the strong dust mite sensitization and absence of evidence for ascariasis, the detected Ascaris-specific IgE was interpreted as a result of IgE cross-reactivity, most likely mediated by shared pan-allergens such as tropomyosin. Prior Enterobius infestation was considered an unlikely contributor to the observed IgE profile. This case highlights the risk of overinterpreting helminth-specific IgE results in highly atopic children and underscores the importance of clinical correlation. In the context of severe house dust mite sensitization, Ascaris lumbricoides–specific IgE positivity most likely reflected allergen cross-reactivity rather than true parasitic infection. This case highlights the importance of interpreting helminth-specific IgE results within the clinical context to avoid diagnostic error and inappropriate management.