Evidence for Asthma in the Lungs of Mice Inoculated with Different Doses of <it>Toxocara canis</it>

Toxocara canis, a common roundworm that mainly causes toxocariasis, is a zoonotic parasite found worldwide. Humans, an accidental host, can acquire T. canis infection through accidental ingestion of T. canis-embryonated egg-contaminated food, water, and soil, and by encapsulated larvae in a paratenic host's viscera or meat. Long-term residence of T. canis larvae in a paratenic host's lungs may induce pulmonary inflammation that contributes to lung injury, airway inflammatory hyperresponsiveness, and collagen deposition in mice and clinical patients. This study intended to investigate the relationship between T. canis infection and allergic asthma in BALB/c mice inoculated with high, moderate, and low doses of T. canis eggs for a 13-week investigation. The airway hyperresponsiveness (AHR) to methacholine, collagen deposition, cytokine levels, and pathological changes in lung tissues was assessed in infected mice at weeks 1, 5, and 13 postinfection. The cell composition in bronchoalveolar lavage fluid of infected mice was assessed at weeks 5 and 13 postinfection. Compared with uninfected control mice, all groups of T. canis-infected mice exhibited significant AHR, a dose-dependent increase in eosinophilic infiltration leading to multifocal interstitial and alveolar inflammation with abundant mucus secretion, and collagen deposition in which the lesion size increased with the infective dose. Infected mice groups also showed significant expressions of eotaxin and type 2 T-helper-dominant cytokines such as interleukin (IL)-4, IL-5, and IL-13. Overall, these results suggest that T. canis larval invasion of the lungs may potentially cause pulmonary inflammatory injury and could subsequently contribute to the development of allergic manifestations such as asthma.