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]

  There are acute attacks of fever, nausea, breathlessness and cough a few hours after exposure. [medical-dictionary.thefreedictionary.com]

• 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]

  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]

  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]

  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]

  As the exposure to this moldy hay becomes chronic, symptoms of respiratory illness start to surface. [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]

• 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]

• Severe Clinical Course

  On the basis of several factors (severity of exposure, duration, etc.), three distinct clinical courses have been described: Acute - After severe exposure to very large quantities of microorganisms, respiratory symptoms in the form of rapidly progressing [symptoma.com]

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].

• 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]

• Saccharopolyspora Rectivirgula

  BACKGROUND: Recent studies in France have shown that Absidia corymbifera and, to a lesser degree Eurotium amstelodami and Wallemia sebi, play a role in farmer's lung disease (FLD), but that Saccharopolyspora rectivirgula, classically incriminated, does [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]

  This may include exposure to Saccharopolyspora rectivirgula, Thermoactinomyces vulgaris, Thermoactinomyces viridis, or Thermoactinomyces sacchari. These species are usually found in decaying organic matter, such as compost, hay or sugar cane. [news-medical.net]

• Decreased Lung Compliance

  [7, 8] If the acute exposure is large, a dramatic increase in inflammation leads to increased vascular permeability, which can alter the alveolar capillary units, thus promoting hypoxemia and decreased lung compliance. [emedicine.com]

Twenty patients were given prednisolone treatment for 8 wk. Sixteen patients received an 8-wk placebo treatment. One patient was withdrawn from the analysis when she terminated corticosteroid treatment because of side effects. [ncbi.nlm.nih.gov]

Medical treatments DO NOT "cure" Farmer's Lung disease. Medical treatments at best manage the severity of the symptoms but offer no hope of reversing the effects of mold on the lungs and body. [selfgrowth.com]

We compared the clinical findings and the prognosis between 12 smokers (SM-FLD) and 31 non-smokers with FLD (NS-FLD). [ncbi.nlm.nih.gov]

[…] dust from feathers and faeces mushroom worker's lung is an allergic response to thermophilic actinomycetes spores in mould maltworker's lung - Aspergillus clavatus spores Links: pathology aetiology clinical features investigations diagnosis management prognosis [gpnotebook.co.uk]

Prognosis 38. The natural history of the disease is variable and probably depends on the type and duration of antigen exposure and the host immune response. [slideshare.net]

Abstract To confirm the main etiological antigen of farmer's lung in Dafeng County, Jiangsu Province, People's Republic of China, precipitins in serum from 30 patients with farmer's lung were tested with several strains of antigens. [ncbi.nlm.nih.gov]

Sheer speculations about the cause of these syndromes have given way to specific disease causes and genetic mapping of the etiologic agents of Farmer’s Lung. [oatext.com]

Abstract We performed a nationwide epidemiologic study of hypersensitivity pneumonitis (HP) in Japan by questionnaire and found that 835 cases of HP were recognized during the 1980s; 74.4% were summer-type HP, 8.1% farmer's lung, 4.3% ventilation pneumonitis [ncbi.nlm.nih.gov]

Epidemiology Frequency United States Farmer's lung is one of the most frequent types of hypersensitivity pneumonitis. [emedicine.com]

[…] alveolitis” describes the cause and nature of the disease, as follows: Extrinsic refers to an external cause Allergic refers to the hypersensitivity reaction that is characteristic of the disease Alveolitis refers to inflammation of the alveoli in the lungs Epidemiology [news-medical.net]

The aim of this study was to gain new insights into the pathophysiology of acute farmer's lung using cardiopulmonary exercise testing. [ncbi.nlm.nih.gov]

Extrinsic Allergic Alveolitis - Pathology mini tutorial Pathophysiology Extrinsic allergic alveolitis is caused by inhalation of antigens that cause a hypersensitivity reaction in the respiratory system. [news-medical.net]

•Introduction •Definition •Aetiology •Pathophysiology •Clinical picture •Smoking •Investigations •Diagnostic criteria •Differential diagnosis •Treatment •Prognosis 3. Introduction 4. [slideshare.net]

Clearly, the risks of ignoring these preventive measures are not worth taking. [nasdonline.org]

The main treatment is avoidance of the antigen, so it is essential to educate patients on preventive measures. To date, no controlled studies have assessed the role of immunosuppressive therapy in this disease. [ncbi.nlm.nih.gov]

• Wear a mask or respirator that prevents dust inhalation. [ohiofarmer.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.