Farmer's lung disease is the main form of occupational hypersensitivity pneumonitis (see this term), caused by chronic inhalation of microorganisms, often thermophilic actinomycetes and less commonly saccharopolyspora rectivirgula, living in mouldy hay, straw, or grain. It is characterized by variable degrees of dyspnea, cough, tiredness, headaches and occasional fever/night sweats, with acute, sub-acute or chronic clinical course