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What is A 33-year-old farmer complains of recurrent episodes of wheezing after working in a barn where hay is stored. On auscultation, there are bibasilar crackles and heart sounds are normal. His laboratory work is normal with no increase in eosinophils and the chest x-ray (CXR) reveals patchy lower lobe infiltrates. Which of the following is the most likely diagnosis? and explain in detail?
Hypersensitivity pneumonitis is an inflammatory disorder of the lungs involving alveolar walls and terminal airways that is caused by repeated exposure to organic agents. In this example of "farmer's lung," the inhalation of antigens present in moldy hay such as thermophilic actinomyces or Aspergillus species are the causative agents. When exposure to moldy hay is stopped, symptoms and signs of farmer's lung all tend to abate and complete recovery usually follows. In acute syndromes, the presentation is 4-8 hours after exposure. Symptoms include fever, chills, malaise, cough, and dyspnea without wheezing. The rate of disease depends on rainfall (which promotes fungal growth) and agricultural practices related to turning and stacking hay. In acute and subacute presentations, removing exposure to the antigen will result in complete recovery.