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What is Farmers lung and explain in detail?
Farmers lung (not to be confused with silo-fillers disease) is a hypersensitivity pneumonitis induced by the inhalation of biologic dusts coming from hay dust or mold spores or any other agricultural products. It results in a type III hypersensitivity inflammatory response and can progress to become a chronic condition which is considered potentially dangerous.

Signs and symptoms
Acute Stage: Appears four to eight hours after exposure.  Symptoms such as headache, irritating cough, and shortness of breath upon physical exertion.
Subacute Stage: Symptoms persist without further exposure, and increase in severity. Symptoms include: shortness of breath upon exertion, chronic coughing, physical weakness, occasional fever and sweating, decrease in appetite, aches and pains.
Chronic Stage: Debilitating effects are now considered long-term. Symptoms include: severe shortness of breath, chronic coughing, physical weakness, occasional fever and sweating at night, decrease in appetite, and general aches and pains.These symptoms develop between four and eight hours after exposure to the antigens.  In acute attacks, the symptoms mimic pneumonia or flu.  In chronic attacks, there is a possibility of the victim going into shock and dying from the attack.

Causes
Permanent lung damage can arise due to ones inability to recognize the cause of symptoms. Farmers lung occurs because repeated exposure to antigens, found in the mold spores of hay, crops, and animal feed, triggers an allergic reaction within the farmers immune system. The defense mechanisms of the body present as cold and flu-like symptoms that occur in individuals who experience either acute or chronic reactions.The mold spores are inhaled and provoke the creation of IgE antibodies that circulate in the bloodstream, these types of immune response are most often initiated by exposure to thermophilic actinomycetes (most commonly Saccharopolyspora rectivirgula), which generate IgG-type antibodies. Following a subsequent exposure, IgG antibodies combined with the inhaled allergen to form immune complexes in the walls of the alveoli in the lungs. This causes fluid, protein, and cells to accumulate in the alveolar wall which slows blood-gas interchange and compromises the function of the lung.  After multiple exposures, it takes less and less of the antigens to set off the reaction in the lung.

Prevention
Farmers lung disease (FLD) is permanent and cannot be reversed, therefore in order to prevent the onset of further stages, farmers should inform their doctor of their occupation and if they have mold in their work environment. Prevention of this respiratory illness can be facilitated through the ventilation of work areas, drying of materials, and the use of a mask when working in confined areas with moldy hay or crops.

Diagnosis
Diagnoses of Farmers lung is difficult due to its similarity to cold and flu-like symptoms