Farmer's lung

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Shaik Aisha sultana, [2]

Farmer’s lung is an allergy related disease usually caused by breathing in the dust from moldy hay. However, dust from any moldy crop – straw, corn, silage, grain, or even tobacco – can also cause Farmer’s Lung. Other potential sources of dust particles include, grain handling, feed handling and processing, and livestock confinement systems.

The disease causes shortness of breath and a feeling of general illness, either in a sudden attack or as a slow, progressive disease. When people with Farmer’s Lung can avoid breathing in dust from moldy crops or feed, they seldom have further problems. On the other hand, lengthy exposure can cause permanent lung damage, physical disability, or even death.

Usually, people with Farmer’s Lung do not associate their health problem with exposure to moldy hay. Instead, they go to their doctor complaining of breathing problems. It is important to recognize the danger of working with moldy crops and to be able to recognize the signs and symptoms of Farmer’s Lung. This enables people with symptoms to get medical help before it becomes a serious illness.

Farmer’s lung disease is a hypersensitivity reaction to organic antigens inhaled from moldy hay. It was the first hypersensitivity pneumonia described. It is the most prevalent and best studied hypersensitivity pneumonia today. If unrecognized, it can cause severe disability and death.

Farmer’s lung was discovered as early as 1713.

• The effect of the Aspergillus and Actinomyces antigens in farmers was described in 1713.

• In 1932, in britain, Campbell described about disorder of the lung caused by inhalation of dust from mold hay.
• In 1964, Ramazzini and Wright described workers getting disease of the chest.^[1]

Farmer’s lung disease is classified into 3 types based on the frequency and intensity of the exposure to the offending agent.

It is classified into acute, sub acute and chronic.

Farmer’s Lung Disease may be classified according to frequency and intensity of exposure into 3 types:

• Acute-symptoms appear 3-4 hours after exposure.
• Sub acute-temporal relation is lost.
• Chronic-temporal relation is lost, slowly progressive dyspnea.^[1]

The pathogenesis of the Farmer’s lung disease is type 3 or type 4 hypersensitivity reaction.

Hypersensitivity reaction because of the many immunologic phenomenon present and antibodies of organism invasion into tissues.

• Type 3 hypersensitivity
• When moldy hay antigens complex with antibodies, to bind complements and attract neutrophils, causing inflammation by release of their toxic enzymes and radicals.^[1]

• Type 4 hypersensitivity
• mononuclear cell inflammation and granuloma.

Sensitized pulmonary alveolar macrophages activated by antigen attract neutrophils and also modulate T cell activity leading to appearance of mononuclear cells and granuloma.^[2]

There are no established genetic predispositions.

There are no associated conditions.

• Pulmonary alveolar wall and interstitial accumulation of neutrophils, mononuclear cells and edema.
• Obstructive bronchiolitis and capillary inflammation is present.

• mononuclear cell predominant
• presence of noncaseating granuloma

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Shaik Aisha sultana, [2]

Farmer’s lung disease is caused by inhaling the spores of the fungus from stored food grains or moldy hay.

• Mold spores which are produced by micro organisms which grow in baled hay, stored grain, or silage with a high moisture content (30 percent) are main causes of Farmer’s Lung. They become active when temperatures reach 70 degrees Fahrenheit in poorly ventilated areas.
• Farmer’s Lung is also more common on dairy farms, especially those not equipped with automated equipment for handling hay or feed.
• Heavy concentrations of mold spores appear as a dry, white or gray powder in grain or forage. When the feed is moved, billions of these microscopic sized particles become airborne and attach themselves to dust.
• These particles pass through the nose, hair, and throat, mucous and accumulate in the lungs where they can cause an allergic type of pneumonia.
• Organic antigens-thermophilic actinomycetes^[1]
• Inorganic substances- isocyanate

Farmer’s lung disease must be differentiated from other diseases that cause cough, dyspnea such as Interstitial lung disease, sarcoidosis and asthma.

Farmer’s lung disease should be differentiated from other occupational lung diseases and diseases causing cough and dyspnea, like:

• Interstitial Lung disease
• Sarcoidosis
• Idiopathic pulmonary fibrosis
• Lung disease in collagen vascular disease
• Pulmonary mycotoxicosis
• Asthma^[1]

Farmer’s lung disease is more prevalent in damper climates and after wet harvest season. It is more commonly observed in men as they are more exposed to the offending agent. Peak incidence of cases is from late winter to early spring.

• Farmer’s lung disease is more prevalent in damper climates, especially after wet harvest season.
• In USA, rates vary from 0.42% in Wisconsin to 3% in Wyoming.
• In Scotland- rates vary from 2.3%-8.6% in farmers of varying regions.^[1]

• If not properly diagnosed or recognized, with Farmer’s lung disease or antigen exposure, about 50% will be disabled with in 5 years, and about 10% will die.

• Patients of all age groups may develop Farmer’s lung disease.
• Farmer’s lung disease is observed to be less prevalent in children.

• There is no racial predilection to Farmer’s lung disease noted.

• Farmer’s lung disease is more prevalent in men as they are often exposed to the offending agent.
• Women and children have less observed prevalence rates.

• Farmer’s lung disease is more prevalent in damper climates.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Shaik Aisha sultana, [2]

The risk factors for Farmer’s lung include excessive exposure to moldy hay or any other offending agent.If patient is having underlying lung pathology, he will be at more risk of developing the cough or breathlessness.

• Farmer’s Lung is a risk for adults who breathe dust from moldy hay or other moldy crops.

• The degree of risk depends on the amount of dust that has collected in the person’s lungs. There is little danger working with loose hay in an open field. The risk increases when farmers or farm workers are breaking open bales of moldy hay or straw inside closed barns or cow sheds. A person can inhale an extremely large amount of dust within a very short time while working indoors.

• Other people exposed to dust from moldy hay; straw or grain include grain handlers, stable employees, poultry workers, and pet shop workers.

• Smokers have risk of developing insidious, worsening dyspnea due to chronic Farmer’s lung disease.^[1]

If left untreated and unrecognized, about 50% of the patients will be disabled with in 5 years, and about 10% will die.Most of the patients with acute disease will have complete resolution of symptoms when they are moved away from the exposure(offending agent). Patients who have multiple exposures to the offending agent are at risk of pulmonary fibrosis.

• Farmer’s lung disease if left untreated, 50% of the patients will be disabled with in 5 years and about 10% will die.^[1]
• About 70-90% Farmer’s lung disease cases have antibodies, 6-20% healthy farmers have antibodies and about 5% office workers have them.

• Common complications of Farmer’s lung disease include Pulmonary fibrosis, some may go on to have chronic lung disease.

• Prognosis is generally excellent in acute disease. There will be complete resolution if the patient is moved away from exposure.
• Multiple attacks can lead to pulmonary fibrosis.
• Patients who are exposed to the offending agent chronically, may develop insidious and worsening breathlessness leading to chronic Farmer’s lung disease.
• In advanced disease, a small proportion will continue to deteriorate inspite of the inciting factor being removed.