Farmer's lung, as a separate clinical entity, is one of the subtypes of hypersensitivity pneumonitis (HP), an autoimmune-mediated disorder of the lung parenchyma [1] [2]. The pathogenesis starts with inhalation of dust from hay or grain containing thermophilic microorganisms (temperatures between 40-60 degrees celsius are optimal for their growth), most commonly occurring under two circumstances - in late winter months when farmers handle very large quantities of hay for feeding purposes; and in very damp and humid conditions (from heavy rain), which are favorable for thermophilic microbial growth [1] [3]. Thermoactinomyces species (T. sacchari, T. vulgaris, T. viridis) and Saccharopolyspora rectivirgula are notable bacterial pathogens, whereas several fungal species (Aspergillus and Penicillium) have been linked to farmer's lung as well [1] [4]. When these microorganisms are inhaled, a hypersensitivity reaction leads to the formation of antigen-antibody immune complexes and the appearance of symptoms [1]. On the basis of several factors (severity of exposure, duration, etc.), three distinct clinical courses have been described [1] [2] [5]:

• Acute - After severe exposure to very large quantities of microorganisms, respiratory symptoms in the form of rapidly progressing dyspnea with a cough appear within several hours and are sometimes accompanied by fever and malaise [1] [5]. Resolution of symptoms is seen after a period of several days [6]. Recurrences of the acute form of farmer's lung have been described in patients with preexisting chronic obstructive pulmonary disease (COPD) [6].
• Subacute - A somewhat less severe clinical course is encountered in the subacute form of farmer's lung, characterized by general malaise, asthenia, anorexia, dyspnea and cough [1] [5].
• Chronic - Prolonged exposure to lower concentrations results in chronic and insidious symptoms. Chronic farmer's lung, which may last for weeks or months, manifests as a slowly progressive dyspnea on exertion, a dry cough, together with weight loss, fatigue, and digital clubbing [1] [5].

• Fever

  Furthermore, his disease does not fit the entities known as grain fever and organic dust toxic syndrome. We believe that this patient presented a different entity that we coined "farmer's fever." [ncbi.nlm.nih.gov]

  Doctors diagnose patients with Farmer's lung under the following conditions: Patient exhibit a clinical history of symptoms such as cough, fever, and labored breathing when exposed to mold in work environment. [en.wikipedia.org]

  Depending on the severity of exposure, patients can suffer from acute, subacute, or chronic respiratory (dyspnea, cough) and constitutional symptoms, as well as fever. [symptoma.com]

  So tell your doctor about any symptoms like breathing problems, chills and fevers. Keep hay, grains and other organic materials dry as fungal spores can only grow in moist conditions. Last updated: 5th February, 2019 [farmerhealth.org.au]

• Fatigue

  Abstract A boy and a girl, 10 weeks and 3 years of age, respectively, were admitted to our department with low temperature, dry cough, fatigue and weight loss. [ncbi.nlm.nih.gov]

  Chronic farmer's lung, which may last for weeks or months, manifests as a slowly progressive dyspnea on exertion, a dry cough, together with weight loss, fatigue, and digital clubbing. [symptoma.com]

  The loss of energy and fatigue is due to the lack of oxygen getting to all parts of the body, as the exchange of gases in the lungs becomes less and less efficient. [ohiofarmer.com]

  Clubbing Generalized fatigue Causes of Farmer’s Lungs Farmer’s lung is not an infectious condition. Pneumonitis refers to any type of lung inflammation and includes pneumonia, a term usually reserved for a lung infection. [healthhype.com]

• Exposure to Moldy Hay

  Asymptomatic farmers (n 12) and normal volunteers with no prior exposure to moldy hay (n 15) were used as control subjects. [ncbi.nlm.nih.gov]

  To diagnose Farmer's Lung, the treating physician will first take a detailed history, especially the occupational history to look for exposure to moldy hay. [epainassist.com]

  Usually, people with Farmer's Lung do not associate their health problem with exposure to moldy hay. Instead, they go to their doctors complaining of breathing problems. [ccohs.ca]

• Constitutional Symptom

  Therapy requires removal of the patient from the offending antigens, although corticosteroids may be useful for constitutional symptoms. [ncbi.nlm.nih.gov]

  Depending on the severity of exposure, patients can suffer from acute, subacute, or chronic respiratory (dyspnea, cough) and constitutional symptoms, as well as fever. [symptoma.com]

• Pathologist

  DESIGN: Retrospective study in which a blinded analysis of 105 TBBs with adequate material from patients with parenchymal diseases (55 cases of FL matched with 50 control samples) was performed by two independent pathologists. [ncbi.nlm.nih.gov]

• Pulmonary Disorder

  Definition of farmer's lung : an acute pulmonary disorder characterized by sudden onset, fever, cough, expectoration, and breathlessness that results from the inhalation of spores in dust from moldy hay or straw First Known Use of farmer's lung 1945, [merriam-webster.com]

  Farmer’s lung, also called thresher’s lung or harvester’s lung, a pulmonary disorder that results from the development of hypersensitivity to inhaled dust from moldy hay or other fodder. [britannica.com]

  Hypersensitivity pneumonitis (HP), also known as extrinsic allergic alveolitis, represents a group of pulmonary disorders mediated by an inflammatory reaction to inhalation of an allergen. [radiopaedia.org]

• Rales

  The clinical features were fatigability, weight loss, recurrent fever, dry cough, pulmonary rales, and clubbing. Serologic studies for precipitins to Micropolyspora faeni were positive. [ncbi.nlm.nih.gov]

  […] hay, an ideal growth medium for the fungi– Microspora vulgaris, Thermoactinomyces vulgaris, and Micropolyspora faeni— implicated in FL Clinical Attacks of several days duration from May to October–the growing season in the Northern Hemisphere, causing rales [medical-dictionary.thefreedictionary.com]

• Exertional Cough

  coughing up blood at an advanced stage. [health.ccm.net]

• Severe Clinical Course

  Subacute - A somewhat less severe clinical course is encountered in the subacute form of farmer's lung, characterized by general malaise, asthenia, anorexia, dyspnea and cough. [symptoma.com]

• Exertional Headache

  Typical Symptoms: severe shortness of breath with any exertion headache irritating cough Subacute State This condition is more serious because the symptoms will be more severe and will last longer even with no further exposure to mold spores. [nasdonline.org]

The diagnosis of farmer's lung can be made only if adequate clinical suspicion is raised, which should be based on information obtained from a detailed patient history and thorough physical examination. During history taking, the physician must gather data about the patient's occupancy, in order to assess potential exposure to thermophilic pathogens [1]. The physical examination may further aid in making a presumptive diagnosis by detecting dry crackles when auscultating the lungs [1]. After a careful assessment of signs and symptoms, imaging studies should be ordered. Plain radiography is usually the first radiograph employed, showing diffuse infiltrates in a ground glass pattern and patchy opacities, but high-resolution computed tomography (HRCT) is the gold standard for evaluation of the lung parenchyma in patients suffering from hypersensitivity pneumonitis [1] [5]. In addition to imaging studies, laboratory testing for precipitating immunoglobulin (Ig) G antibodies, skin prick testing, bronchial challenge testing using appropriate antigens, and spirometry are constitutive features of the workup [1] [3] [5]. Some authors advocate that a transbronchial biopsy (TBB) with subsequent histopathological examination should be obtained in order to solidify the diagnosis [1].

• Ground Glass Appearance

  The chest roentgenogram showed a ground-glass appearance with air bronchogram. The open lung biopsy material was typical for alveolitis, with minute interstitial granulomas and obliteration of lung parenchyma. [ncbi.nlm.nih.gov]

  CT scans show pulmonary cysts and a diffuse ground-glass appearance [19]. Patients who avoid contact with the antigen complex for a sustained period demonstrate relief from the disease. [oatext.com]

• Pulmonary Infiltrate

  FARMER'S lung resembles Loeffler's syndrome, for, at times, it manifests the triad of pulmonary infiltrations, eosinophilia and a benign clinical course. [nejm.org]

• Air Bronchogram

  The chest roentgenogram showed a ground-glass appearance with air bronchogram. The open lung biopsy material was typical for alveolitis, with minute interstitial granulomas and obliteration of lung parenchyma. [ncbi.nlm.nih.gov]

• Neutrophil Count Increased

  During these episodes the blood neutrophil count increases. [ncbi.nlm.nih.gov]

• Micropolyspora Faeni

  Massive amounts of mould spores were cultured from the residential areas, and, in addition, the male patient had an elevated titer to Micropolyspora faeni and the female patient, elevated titers to Thermoactinomyces vulgaris, Micropolyspora faeni, Aspergillus [ncbi.nlm.nih.gov]

• Thermoactinomyces Vulgaris

  vulgaris, in addition to spirometry, pulmonary diffusing capacity (DL(CO)), and the evaluation of chronic bronchitis. [ncbi.nlm.nih.gov]

  vulgaris ICD-9-CM Volume 2 Index entries containing back-references to 495.0 : [icd9data.com]

1. Cano-Jiménez E, Acuña A, Botana MI, et al. Farmer's Lung Disease. A Review. Arch Bronconeumol. 2016;52(6):321-328.
2. Selman M, Pardo A, King TE. Hypersensitivity pneumonitis: insights in diagnosis and pathobiology. Am J Respir Crit Care Med. 2012;15:314–324.
3. Bourke SJ, Dalphin JC, Boyd G, McSharry C, Baldwin CI, Calvert JE. Hypersensitivity pneumonitis: current concepts. Eur Respir J Suppl. 2001;32:81s–92s
4. Spagnolo P, Rossi G, Cavazza A, et al. Hypersensitivity Pneumonitis: A Comprehensive Review. J Investig Allergol Clin Immunol. 2015;25(4):237-250.
5. Lacasse Y, Cormier Y. Hypersensitivity pneumonitis. Orphanet J Rare Dis. 2006;1:25.
6. Malinen AP, Erkinjuntti-Pekkanen RA, Partanen PLK, Rytkönen HT, Vanninen RL. Long-term sequelae of farmer’s lung disease in HRCT: a 14-year followup study of 88 patients and 83 matched control farmers. Eur Radiol. 2003;13: 2212–21.