"Look What the Cat Dragged In": Delayed-Onset Hypersensitivity Pneumonitis Due to Pregnancy

Hypersensitivity pneumonitis (HP) is an immune-mediated inflammatory lung disease triggered by the inhalation of environmental antigens. Bird fancier's lung is a common subtype, whereby the hypersensitivity reaction is triggered by exposure to avian proteins from bird feathers and droppings. This case describes a woman in her 20s, presenting at 16 weeks postpartum, with progressive dyspnoea, dry cough, and hypoxia. A thorough social history revealed significant exposure to a pigeon after the woman had rescued a pigeon from her cat and nursed it back to health during her third trimester. Computed tomography (CT) imaging revealed diffuse pulmonary nodules and air trapping, and subsequent serology confirmed elevated IgG to avian proteins. The patient was diagnosed with bird fancier's lung and managed with corticosteroids. The pigeon was relocated to avoid further exposure. It is proposed that the Th2-dominant immune profile during pregnancy leads to an anti-inflammatory state, suppressing Th1-driven conditions such as HP and delaying symptom onset until the postpartum immune rebound. Recognition of this immunological shift is critical in postpartum patients with atypical respiratory symptoms. Timely history-taking, specialist input, and consideration of environmental triggers were key to swift diagnosis and management in this case.