Hypersensitivity granulomatous pneumonitis caused by the inhalation of avian antigens that are present in the dust of the droppings and feathers of many species of birds. In the acute phase it manifests as fever, chills, dyspnea, cough, and chest tightness. Chronic exposure may lead to interstitial lung fibrosis. The disease is Monarch Disease Ontology entry MONDO_0005668 (bird fancier's lung). Also known as: Avian hypersensitivity pneumonitis, bird breeder's lung, bird fancier lung, bird-fancier's lung, bird-fanciers' lung, pigeon breeder's lung, pigeon-breeder lung disease, pigeon-breeder's lung.