What is the definition or description of: hypersensitivity pneumonitis?

Extrinsic alveolitis: A non-ige mediated, immunologically mediated lung disease with generalized symptoms due to sensitization of a wide variety of inhaled organic dusts. These include molds, birds and other antigens found especially in workplaces and hobbies. It affects lung alveoli and can have acute (appears like viral pneumonia), subacute and chronic forms. No one test confirms the disease.

Pneumonia from dusts: Hypersensitivity pneumonitis is a special form of lung irritation/inflammation caused by the body's response when certain kinds of dusts are inhaled. The dusts are organic, meaning they come from animals or plants. People who work where they are exposed to dried material from plants (such as "silo fillers' lung") or animals (such as "bird fancier's lung") are at risk. Diagnosis can be a challenge.