Farmer's lung: symptoms, causes, diagnosis and prevention

Farmer's lung is the best-known example of hypersensitivity pneumonitis, a condition in which the lungs develop an immune response (hypersensitivity) to something, often breathed in, which causes inflammation of the lung (pneumonitis). North Bristol NHS Trust says farmer's lung is caused by breathing in mould that grows on hay, straw and grain. Other forms include bird fancier's lung, caused by feather or bird dropping particles, and disease linked to fungus in humidifiers, heating systems and air conditioners that are not well maintained.

In Farmer's Weekly, a doctor explains that the spores do not cause an infection. Instead they trigger an allergic reaction and irritation in the small air sacs of the lungs. The trigger particles are called allergens. Symptoms may develop after a sudden, large exposure (acute farmer's lung) or after lots of smaller exposures (chronic farmer's lung).

Farmers are at risk because of working in environments such as grain stores and poultry sheds, where dust and spores in the air are common. The same article notes that people often do not link their breathing problems with their working environment, which can delay diagnosis.

The trust describes two patterns. In the acute form, cough, shortness of breath and sometimes fever or flu-like symptoms occur suddenly after exposure. This can go away without lasting damage if the cause can be permanently avoided. In other cases cough and breathlessness come on gradually, perhaps over months or years, following repeated exposure. This can cause permanent scarring (fibrosis) of the lungs.

Farmer's Weekly gives more detail. After a large exposure, symptoms may appear four to six hours later, including a dry cough, shortness of breath, chest tightness and, more rarely, fever and chills, usually resolving within days. In chronic disease the symptoms include increasing breathlessness on moving around and an ongoing dry cough, and the fingertips may become swollen or rounded with changed nail shape, known as clubbing.

• Sudden attack: dry cough, breathlessness, chest tightness, sometimes fever or chills hours after exposure.

• Gradual disease: persistent dry cough and increasing breathlessness on activity.

• Long-term signs: scarring of the lungs and, in some people, clubbing of the fingertips.

Farmer's Weekly says a GP will generally diagnose farmer's lung by asking about symptoms and occupational history, listening to the lungs with a stethoscope and ordering tests of how well the lungs are working and whether there is scarring. A blood test may be ordered if there is a history of exposure.

North Bristol NHS Trust describes the specialist assessment: a detailed history and physical examination; lung function tests, which show how well the lungs work and can be used to monitor disease and response to treatment; a CT scan of the chest, whose patterns can help show whether the disease is active or quiet and whether there is scarring or inflammation; and blood tests that detect proteins to moulds in farmer's lung. Some people have a bronchoscopy, and if the diagnosis is still unclear a lung biopsy may be discussed.

North Bristol NHS Trust says that if a specific cause can be identified, the most important part of treatment is to avoid it. This may mean changing job or using a special mask when exposed. If exposure cannot be stopped, the chance of progression to irreversible scarring increases.

Medicines may be advised to slow or stop the disease getting worse. The trust lists steroids such as prednisolone to reduce inflammation, immunosuppressive medicines, which are sometimes called steroid-sparing agents and need regular blood tests, and antifibrotic medicines if the condition worsens despite other treatment. Asthma and Lung UK, quoted in Farmer's Weekly, says treatments may include steroids over a few weeks or months to ease the inflammation, and that with swift diagnosis and avoidance of the cause a full recovery is likely.

Other measures include pulmonary rehabilitation, an exercise and education programme to manage breathlessness, supplemental oxygen when scarring reduces oxygen reaching the blood, clinical trials, and, for a small minority, assessment for lung transplantation. The trust also advises having seasonal COVID-19 and flu vaccinations and the pneumonia vaccination.

Farmer's Weekly says the most important part of preventing or managing farmer's lung is to reduce exposure to trigger particles. For farmers this means drying crops adequately before storage and ensuring good ventilation. Respiratory protection should be worn by farmers and farm workers when handling stored crops, particularly if they have been stored damp or are likely to be mouldy. The same advice on ventilation and respiratory protection applies to people working with birds.

Because early disease is reversible if the trigger is removed, anyone who develops recurring cough or breathlessness linked to work should mention their occupation to their GP rather than waiting. The trust notes that symptoms will often return if exposed again.

Where scarring has occurred, it cannot be reversed, and Farmer's Weekly says treatment focuses on managing symptoms or slowing further scarring. Pulmonary rehabilitation is designed to support and reassure as well as help with the condition.

North Bristol NHS Trust says keeping active and doing what you enjoy helps, and that people who need help with personal care or getting about may be eligible for benefits such as Personal Independence Payment (PIP). Charities such as Action for Pulmonary Fibrosis and Asthma and Lung UK provide support and information.

On the NHS, farmer's lung is investigated by a GP and, where chronic or unclear, by a respiratory or interstitial lung disease service with lung function tests and CT scanning. Treatment, rehabilitation and oxygen assessment are provided free at the point of use.

Some people seek a private respiratory opinion for quicker CT scanning or specialist review. It is helpful to bring a clear description of work exposures, because identifying the trigger drives both diagnosis and treatment.