It can cause shortness of breath, fever, dry cough, chest pain, anorexia and weight loss, fatigue, and progressive pulmonary fibrosis (the most serious complication).

It is triggered by exposure to avian proteins present in the dry dust of droppings or feathers of a variety of birds.

BFL may be treated with steroids such as prednisone to reduce inflammation, and removal of exposure to avian proteins.

[1] These may be worse after sudden exertion or when exposed to temperature change, which can resemble asthma, hyperventilation syndrome or pulmonary embolism.

[3] In chronic BFL, symptoms may include anorexia,[3] weight loss,[3] extreme fatigue, and progressive pulmonary fibrosis.

Pulmonary fibrosis is generally the most serious consequence of the disease, as it progressively and irreversibly diminishes the lungs' efficiency over time.

Avian proteins include mucins and antibodies, which stimulate a significant immune response from the body.

[2] Extensive exposure to birds, combined with reduced diffusing capacity, are strongly suggestive of BFL.

[3] X-ray or CT scans usually show physical changes to the lung structure (a "ground glass" appearance or a "mosaic" pattern) as the disease progresses.

[1] Precise distribution and types of tissue damage differ among similar diseases, as does response to treatment with prednisone.

[3] Standard bronchoscopy usually shows chronic inflammation of lung tissue, and granulomas with poorly-defined margins.

[7] It is advisable to remove all birds, and bedding and pillows containing feathers, from the patient's home, as well as any down-filled outerwear and sleeping bags.

In extreme cases, patients may be advised to evacuate their homes permanently and to dispose of all possessions that have been exposed to avian proteins if they cannot be cleaned thoroughly inside and out.

Depending on the extent of fibrosis at the time of their diagnosis and how well they follow recommended treatment protocols (especially avoidance of allergens), many BFL patients make a full recovery.