Farmer Lung

Farmer lung is a form of hypersensitivity pneumonitis caused by inhalation of thermophilic actinomycetes (Saccharopolyspora rectivirgula, Thermoactinomyces vulgaris) and fungi from mouldy hay, straw and grain.

• Occurs in farmers working with stored hay in damp conditions in cold, wet climates; prevalence 1 to 3% in exposed farming populations (higher in some regions).
• Acute (4 to 8 hours after heavy exposure), subacute, and chronic fibrotic forms.
• Genetic susceptibility (HLA); non smokers more affected (smoking appears protective for onset but worsens chronic disease).
• Fibrotic disease occurs in 5 to 10% with chronic exposure, reducing survival.

• Acute: fever, chills, malaise, cough, dyspnoea and myalgia 4 to 8 hours after handling mouldy hay, resolving within 1 to 3 days after exposure ends; may recur on re-exposure.
• Subacute/chronic: progressive dyspnoea, dry cough, weight loss, fatigue, crackles, clubbing.
• Squeaks on auscultation.

• Exposure history (mouldy hay, silage, grain) with temporal pattern.
• Serum precipitins to Saccharopolyspora rectivirgula and Aspergillus species (exposure marker; present in up to 20% of exposed asymptomatic farmers).
• HRCT: ground glass, centrilobular nodules, mosaic attenuation, air trapping; fibrosis in chronic cases.
• Spirometry/DLCO: restrictive with reduced DLCO; hypoxaemia on exercise.
• Bronchoalveolar lavage lymphocytosis (over 30%), low CD4/CD8.
• Lung biopsy (if uncertain): poorly formed granulomas, cellular bronchiolitis, interstitial pneumonia.

• Avoid exposure: use dry hay, improve barn ventilation and drying, use silage or pelleted feed, wear respirators (powered air purifying respirators), change duties; complete avoidance may be needed.
• Acute episodes: usually self limited; oxygen and symptomatic therapy; prednisolone 40 to 60 mg daily for 1 to 2 weeks, tapered, in severe cases.
• Subacute/chronic: prednisolone 0.5 mg/kg for 4 to 8 weeks then taper over 3 to 6 months; steroid sparing mycophenolate or azathioprine for relapsing disease.
• Progressive fibrosis: nintedanib 150 mg twice daily.
• Supportive: oxygen, pulmonary rehabilitation, vaccinations.
• Follow up spirometry and DLCO every 3 to 6 months; early diagnosis and antigen removal results in good prognosis.
• Lung transplantation for end stage.