Bird dander lung disease, also known as bird fancier’s lung (BFL), is a type of hypersensitivity pneumonitis caused by exposure to avian proteins found in bird excreta, feathers and serum. It is an occupational lung disease most commonly seen in bird breeders, pet shop workers and pigeon fanciers. BFL causes inflammation of the lung parenchyma and airways resulting in cough, dyspnea and impaired pulmonary function. This article will provide an overview of bird dander lung disease including the epidemiology, pathophysiology, clinical features, diagnostic workup, treatment and prevention.
Epidemiology
BFL is the most common type of hypersensitivity pneumonitis, accounting for about 15-30% of cases. The prevalence ranges from 0.5-22% among pigeon breeders, and 2.5-21% among bird fanciers in general. It occurs most frequently in middle-aged Caucasian men due to their predominance in the poultry business. The time of exposure to avian antigens before onset of symptoms ranges from months to years. Genetic factors likely play a role as disease risk is higher among siblings and other family members of affected individuals. Cigarette smoking and atopy do not appear to predispose people to BFL.
Pathophysiology
BFL is caused by an immune response to repeated inhalation of avian proteins found in bird droppings, feathers, serum and egg products. These proteins include immunoglobulins, intestinal mucin and serum albumin. In susceptible individuals, exposure triggers production of antibodies against the avian antigens. Subsequent inhalation of the antigens leads to formation of antibody-antigen complexes in the distal bronchioles and alveoli resulting in a localized type III hypersensitivity reaction. This stimulates recruitment of lymphocytes, macrophages and neutrophils, causing parenchymal inflammation and damage. The lung reaction is concentrated in the lower lobes due to the preferential deposition of avian proteins in those areas. With repeated exposure, fibrosis may develop due to collagen deposition by fibroblasts.
Clinical Features
BFL typically develops insidiously over months to years of exposure to birds. Symptoms include:
– Exertional dyspnea
– Non-productive cough
– Fever, chills
– Fatigue, malaise
– Loss of appetite and weight loss
On physical exam, expiratory wheezes and crackles may be appreciated on lung auscultation. Finger clubbing can sometimes occur in chronic cases. Most patients develop symptoms 4-8 hours following heavy exposure due to the delayed hypersensitivity reaction. Wheezing may be more prominent after 12 hours. Constitutional symptoms resolve within 24 hours if the antigen exposure stops.
Acute Form
A small subset of individuals develop acute, influenza-like BFL after intense exposure to birds. This consists of abrupt onset fever, chills, dyspnea, headache and body aches beginning 2-9 hours after exposure. It may be accompanied by visible shivers and cyanosis. Symptoms resolve by 24-48 hours after the exposure ends. Recurrence is common with repeated exposure. The acute form appears to result from massive release of cytokines in the lungs in response to high levels of avian antigens.
Subacute Form
In the subacute form, symptoms gradually worsen over several weeks. Dry cough is often the initial complaint followed by exertional dyspnea and fatigue. Systemic symptoms like fever and chills may be absent. Onset is usually rapid after heavy exposure such as cleaning an aviary. Findings on lung exam and chest imaging reflect interstitial inflammation. The subacute form likely represents partially developed hypersensitivity to the avian antigens.
Chronic Form
The chronic form of BFL develops after months to years of moderate but persistent antigen exposure. Exertional dyspnea and cough predominate. Constitutional symptoms are minimal. Clubbing of the fingers can sometimes be seen. Pulmonary function tests show a restrictive pattern with reduced diffusing capacity. Chest CT reveals fibrosis, predominately in the lower lobes. The chronic form is due to recurrent lung injury leading to parenchymal fibrosis.
Diagnosis
BFL is often challenging to diagnose given the nonspecific nature of symptoms. There are no definitive diagnostic tests. It is diagnosed based on a combination of exposures, clinical findings and supportive tests. These include:
Exposure History
A detailed exposure history is key in identifying at-risk patients. Quantity and timing of avian antigen exposure should be characterized. Those with heavy, consistent exposure (e.g. pigeon breeders) are more likely to be affected versus those with sporadic, low-level exposure. Jobs and hobbies involving birds should be documented. Exposure to bird antigens in the 24-48 hours prior to symptom onset strongly supports the diagnosis.
Physical Exam
Lung auscultation may reveal end-expiratory crackles and/or wheezing, particularly in subacute and chronic BFL. Finger clubbing can sometimes be seen in chronic cases. Hypoxemia may be present in more advanced disease. Physical exam is otherwise unremarkable in mild BFL.
Pulmonary Function Tests
Spirometry often shows a restrictive pattern with reduced forced vital capacity (FVC). Forced expiratory volume in 1 second (FEV1) is generally preserved, so ratio of FEV1/FVC is normal or increased. Lung volumes reveal decreased total lung capacity and functional residual capacity. Diffusing capacity of the lungs for carbon monoxide (DLCO) can be moderately to severely reduced. Reduction in DLCO correlates with disease severity better than spirometry.
Chest Imaging
Chest x-ray may be normal early in the disease. With progression, diffuse reticulonodular opacities are seen primarily in the lower lobes. Advanced BFL can demonstrate extensive lung fibrosis. High resolution chest CT is more sensitive, showing ground glass opacities and interlobular septal thickening. Mosaic attenuation and air trapping result from airflow obstruction. Upper lobes are typically spared.
Bronchoalveolar Lavage
Analysis of bronchoalveolar lavage fluid shows increased lymphocytes, with a predominance of CD8+ T-cells. CD4/CD8 ratio is usually less than 1.0. Neutrophils may also be elevated. Lavage fluid can be sent for stains and cultures to rule out infection.
Serum Precipitins
Testing acute and/or convalescent serum for precipitating antibodies to avian serum proteins can help establish the diagnosis. Titers are often elevated, but can be normal in mild or early disease. Serum precipitins have low sensitivity (60%) but high specificity (95%) for BFL.
Inhalation Challenge
Inhalation challenge involves controlled exposure to avian antigens with monitoring for reproduction of symptoms and pulmonary function decline. This can help confirm BFL in ambiguous cases. However, it carries risks and is rarely performed. Safer alternatives include nasal challenge and skin testing.
Lung Biopsy
Surgical lung biopsy shows chronic interstitial inflammation centered on the distal bronchioles. Noncaseating granulomas are sometimes seen. finding giant cells. Advanced cases reveal pulmonary fibrosis. Lung biopsy provides a definitive diagnosis but is invasive. It should be reserved for cases where less invasive methods are inconclusive.
Differential Diagnosis
The differential diagnosis for BFL includes:
– Hypersensitivity pneumonitis from other organic antigens
– Sarcoidosis
– Silicosis
– Chronic beryllium disease
– Respiratory bronchiolitis-associated interstitial lung disease
– Smoking-related interstitial lung disease
– Idiopathic pulmonary fibrosis
Careful exposure history and ancillary testing help distinguish BFL from its mimics. The upper lung predominance on imaging favors HP from non-avian organic antigens. Pulmonary function testing and serum studies help differentiate BFL from the other interstitial lung diseases.
Treatment
The cornerstone of BFL treatment is eliminating further exposure to avian antigens. Medications aim to reduce inflammation and prevent progression to fibrosis. Supportive care optimizes respiratory status. Options include:
Antigen Avoidance
Complete avoidance of bird contact at home and work is essential. This may require transitioning to jobs and hobbies that do not involve birds. Even minimal exposure can trigger recurrence of symptoms and lung inflammation. Strict antigen avoidance results in disease remission in most individuals if implemented early.
Corticosteroids
Oral corticosteroids such as prednisone 0.5 mg/kg/day tapered over 1-3 months helps resolve symptoms and lung inflammation in acute BFL. Low dose maintenance therapy may be required in severe or chronic cases to prevent progression. Inhaled steroids can also be beneficial for airway inflammation. Systemic side effects limit long-term steroid use.
Cytotoxic Agents
Medications that suppress the immune system may be added if steroids alone are inadequate. These include cyclophosphamide, azathioprine and methotrexate. They may allow lower steroid dosing. Clinical response is variable and side effects can be significant.
Supplemental Oxygen
Low dose supplemental oxygen administered by nasal cannula helps correct hypoxemia. This improves dyspnea and exercise tolerance. Pulmonary rehabilitation programs also increase exercise capacity through strength training and desensitization.
Lung Transplant
In advanced BFL with end-stage lung fibrosis, transplantation may be an option in appropriate surgical candidates. Single or double lung transplantation can be considered for those with progressive disease despite optimal medical therapy.
Prognosis
Most patients with BFL improve clinically and functionally with early diagnosis and strict antigen avoidance. Pulmonary function may take months to fully recover. About one-third have complete remission of lung impairment. The remainder have residual lung dysfunction, particularly with late diagnosis and irreversible fibrosis. With ongoing antigen exposure, BFL can result in end-stage lung disease over a period of years. Less than 5% of patients die from BFL, usually from secondary complications like respiratory failure. Cigarette smoking is associated with worse long-term outlook.
Prevention
Preventing the onset of BFL relies on limiting exposure to avian proteins:
– Use personal protective equipment like respirator masks when working with birds
– Perform dust-producing tasks with birds in well-ventilated areas
– Clean up bird droppings and cages frequently using wet mops
– Install exhaust ventilation and HEPA filters in indoor aviaries
– Regularly bathe and groom birds to reduce dander
– Avoid bringing birds into the home
– Cover bird cages when not handling birds
– Promptly wash hands after touching birds
– Wear long sleeves and change clothes after bird contact
At-risk individuals should consider transitioning to jobs and hobbies that do not involve heavy bird exposure. Early diagnosis through screenings for common symptoms can prevent disease progression. Annual evaluations of lung function and symptoms are recommended for bird fanciers despite protective measures.
Conclusion
Bird dander lung disease is a form of hypersensitivity pneumonitis caused by repeated inhalation of avian proteins. It occurs most often in those who work with or keep birds. Symptoms result from lung inflammation and fibrosis triggered by an immune reaction to the antigens. Early diagnosis based on exposures, clinical features and lung function testing is key. Complete avoidance of further antigen exposure is critical to allow the lungs to heal and prevent irreversible damage. Corticosteroids and other immunosuppressants may be warranted in some cases. With proper prevention and treatment, the majority of patients achieve remission of this occupational lung disease. However, advanced cases can lead to chronic respiratory impairment. Increased awareness among those who handle birds is important to allow early recognition and intervention.