Farmer's lung
Hypersensitivity pneumonitis from inhaled agricultural mold spores.
Farmer's lung is a respiratory condition caused by inhaling dust from moldy hay, crops, or other agricultural materials. It falls under a category of lung inflammation known as hypersensitivity pneumonitis (also called hypersensitivity alveolitis or extrinsic allergic alveolitis). The body’s reaction is a type III hypersensitivity response, and if exposure continues, the disease can become chronic and potentially life-threatening. It is distinct from silo-filler's disease.
**Signs and symptoms** Symptoms appear four to eight hours after contact with the trigger. In the acute stage, a person may experience headache, a dry cough, and shortness of breath during physical activity. If the condition progresses to the subacute stage, these symptoms persist even without further exposure and become more severe: ongoing cough, weakness, shortness of breath on exertion, occasional fever and sweating, loss of appetite, and general aches. In the chronic stage, the damage is long-term, with severe shortness of breath, chronic cough, weakness, night sweats, fever, appetite loss, and body aches. Acute episodes can resemble pneumonia or the flu, while chronic attacks may lead to shock and, in some cases, death.
**Causes** Repeated inhalation of mold spores from hay, crops, or animal feed triggers an allergic immune response. The body’s defenses produce symptoms that mimic a cold or flu. The spores prompt the creation of IgE antibodies, but the main immune reaction involves IgG antibodies, typically generated after exposure to thermophilic actinomycetes—most often *Saccharopolyspora rectivirgula*. On later exposure, these IgG antibodies combine with the inhaled allergen, forming immune complexes in the walls of the lung’s alveoli. This buildup of fluid, protein, and cells slows gas exchange and impairs lung function. After multiple exposures, smaller amounts of the antigen can trigger a reaction. Permanent lung damage can occur if the cause goes unrecognized.
**Prevention** Farmer’s lung disease is permanent and cannot be reversed. To prevent progression, farmers should inform their doctor about their occupation and any mold in their work environment. Preventive measures include ventilating work areas, drying materials thoroughly, and wearing a mask when working in confined spaces with moldy hay or crops.
**Diagnosis** Diagnosis is challenging because symptoms res
- field
- Respiratory medicine / Occupational lung disease
- known_for
- Hypersensitivity pneumonitis from agricultural mold spores
- type
- Disease
- affected_population
- Farmers exposed to moldy hay, crops, or animal feed
Lore & Background
Farmer's lung occurs because repeated exposure to antigens found in mold spores of hay, crops, and animal feed triggers an allergic reaction within the farmer's immune system. The mold spores are inhaled and provoke the creation of IgE antibodies, but the immune response is most often initiated by exposure to thermophilic actinomycetes, most commonly Saccharopolyspora rectivirgula, which generate IgG-type antibodies. Following subsequent exposure, IgG antibodies combine with the inhaled allergen to form immune complexes in the walls of the alveoli, causing fluid, protein, and cells to accumulate and compromise lung function.
Reader's Guide
Farmer's lung is significant as a preventable occupational lung disease that can cause permanent damage if unrecognized. Diagnosis is difficult due to its similarity to cold and flu symptoms, relying on clinical history, presence of diffuse lung disease in chronic cases, and antibodies to thermophilic Actinomyces. Prevention through ventilation, drying materials, and mask use is critical, as the disease cannot be reversed once hypersensitivity develops. Acute cases can be treated with rest and reduced antigen exposure, but chronic cases last a lifetime. The disease peaks in late winter and early spring, is most prevalent in damp climates, and is associated with improperly dried hay, especially at the bottom of piles.
Did You Know?
- Farmer's lung is not to be confused with silo-filler's disease.
- The mold spores that cause farmer's lung are most commonly from Saccharopolyspora rectivirgula, a thermophilic actinomycete.
- Symptoms of acute farmer's lung appear four to eight hours after exposure and mimic pneumonia or flu.
- The incidence of farmer's lung peaks during late winter and early spring, mostly after harvest season.
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