- Löffler syndrome in ascariasis is primarily caused by the migration of Ascaris larvae through the pulmonary tissue.
- As these larvae pass through the lungs during their life cycle, they induce a transient eosinophilic pneumonitis, resulting in symptoms like cough, wheezing, and eosinophilia.
- This is a hypersensitivity-like reaction to the mechanical and antigenic irritation caused by the larvae themselves, not the adult worms or their enzymes.
- Secondary infections or toxic enzyme effects are not the main contributors.

Thus, the key factor is the larval migration through lung tissue, which leads to the characteristic clinical and radiologic findings of Löffler syndrome.

Reference: Robbins Basic Pathology, 10th Edition, Chapter 9: Pulmonary Infections and Lung Pathology