Paradoxical Use of Benralizumab in Reactive Hypereosinophilia from Toxocariasis and Tuberculosis Co-Infection—Case Report and Literature Review

Tuberculosis and parasitic infections, including <i>Toxocara</i>, frequently coexist in many regions worldwide, yet their interaction remains poorly understood. Tuberculosis triggers a type 1 immune response characterized by IL-12, IFN-γ, and TNF-α production, while toxocariasis elicits a type 2 response, mediated by cytokines such as IL-4, IL-5, IL-13, and IL-33. The coexistence of these divergent immune pathways can disrupt immune regulation and impair the host's ability to control both infections, potentially leading to persistent hypereosinophilia. We illustrate this complex interplay through a real-world case involving a heavy smoker in whom <i>Toxocara</i> infection likely reactivated latent tuberculosis, resulting in severe, unexplained hypereosinophilia and late-onset asthma with recurrent exacerbations. After excluding other causes and completing full antituberculosis therapy along with three courses of antiparasitic treatment and systemic corticosteroids, hypereosinophilia persisted. The introduction of benralizumab, a biologic therapy targeting IL-5Rα, led to a rapid reduction in eosinophils to normal ranges and significant clinical improvement. This case underscores the diagnostic and therapeutic challenges posed by the intersection of common infections and highlights that even a neglected parasitic infection such as toxocariasis can underlie severe respiratory complications with eosinophilia, where paradoxically biologic therapy may ultimately provide a very effective intervention.