• Who it affects: Primarily adults who work in close, daily contact with animals—zookeepers, veterinary staff, laboratory animal caretakers, pet shop employees, and wildlife rehabilitators. Cases have also been reported in hobbyist bird‑keepers and people who keep exotic pets at home.
• Prevalence: Exact global numbers are unclear because HP is often under‑diagnosed. In the United States, occupational HP accounts for roughly 1–2 % of all respiratory diseases in animal‑handling professions. A European survey of zoo staff found a serologic sensitization prevalence of 8–12 % and a symptomatic disease prevalence of 1–3 % (Fujita et al., 2021).
• Age & gender: Most cases occur between 30‑60 years of age; slight male predominance mirrors the gender distribution of zoo‑care occupations.

Symptoms

HP can present in three patterns: an acute “flu‑like” reaction after heavy exposure, a sub‑acute phase with ongoing low‑grade exposure, or a chronic fibrotic stage after years of untreated inflammation. Symptoms may overlap with asthma, bronchitis, or viral infections, which contributes to delayed diagnosis.

Acute (hours–days after exposure)

• Fever & chills – often low‑grade (37.5‑38.5 °C).
• Dry cough – sudden onset, non‑productive.
• Shortness of breath – may feel like “tight chest” after cleaning an animal enclosure.
• Body aches & fatigue – similar to viral illness.
• Chest tightness or pleuritic pain – rarely sharp.

Sub‑acute (weeks–months of intermittent exposure)

• Persistent dry cough.
• Gradual dyspnea on exertion (e.g., climbing a flight of stairs).
• Low‑grade fever or nocturnal sweats.
• Weight loss & reduced appetite.
• Fine crackles heard on lung auscultation (“Velcro” sounds).

Chronic (months–years of untreated disease)

• Progressive dyspnea at rest.
• Chronic dry cough.
• Fatigue & loss of stamina.
• Finger clubbing (in advanced fibrosis).
• Signs of pulmonary hypertension (swelling of ankles, rapid heartbeat).

Because symptoms are non‑specific, any zoo employee who develops new or worsening respiratory complaints should consider HP, especially if symptoms improve when away from work.

Causes and Risk Factors

HP results from an abnormal immune response to inhaled antigens. In the zoo setting, the most common culprits are:

• Bird proteins – feathers, droppings, and serum from parrots, pigeons, waterfowl, and raptors.
• Rodent proteins – mouse, rat, guinea‑pig urine and dander.
• Exotic mammals – primates, marsupials, and carnivores can shed dander and saliva containing high‑molecular weight proteins.
• Mold & fungi – grow on hay, bedding, or moist enclosure surfaces.

Risk Factors

• Occupational exposure – daily cleaning of cages, feeding, handling or necropsy work without adequate ventilation.
• Enclosure design – poorly aerated indoor habitats, high humidity, and accumulation of bedding material.
• Personal susceptibility – previous atopy (asthma, allergic rhinitis), smoking, or existing lung disease.
• Genetic predisposition – certain HLA‑DR alleles have been linked to heightened HP risk (Davis et al., 2020).
• Duration & intensity of exposure – risk rises sharply after 5–10 years of continuous work in high‑antigen environments.

Diagnosis

Diagnosing zookeepers’ lung requires a combination of clinical suspicion, exposure history, and objective testing. No single test is definitive.

1. Detailed History & Physical Examination

• Document specific animal contact, duration, and protective measures used.
• Listen for inspiratory crackles and assess oxygen saturation.

2. Pulmonary Function Tests (PFTs)

Typical pattern: a restrictive defect with reduced total lung capacity (TLC) and a decreased diffusing capacity for carbon monoxide (DLCO). Obstructive changes may coexist if asthma is present.

3. Imaging

• Chest X‑ray: May be normal early; later shows diffuse haziness.
• High‑Resolution CT (HRCT): Gold standard. Findings include ground‑glass opacities, centrilobular nodules, and, in chronic disease, reticulation or honey‑comb fibrosis.

4. Laboratory Tests

• Complete blood count – often shows mild leukocytosis.
• Serum precipitating antibodies (IgG) against specific animal antigens. Positive results support exposure but are not diagnostic alone.

5. Bronchoscopy with Bronchoalveolar Lavage (BAL)

Typical BAL fluid shows a lymphocytosis > 20 % (often 40–60 %). This helps differentiate HP from other interstitial lung diseases.

6. Lung Biopsy (Surgical or Transbronchial)

Reserved for uncertain cases. Histology reveals a combination of cellular bronchiolitis, poorly formed granulomas, and interstitial inflammation.

7. Provocative Antigen Challenge (Optional)

Re‑exposure in a controlled setting (e.g., short‑duration inhalation of the suspected antigen) may reproduce symptoms and physiologic changes, confirming diagnosis. Should only be performed in a specialized center.

Reference: American Thoracic Society & European Respiratory Society guidelines for hypersensitivity pneumonitis, 2021.

Treatment Options

Management focuses on removing the inciting antigen, controlling inflammation, and preventing progression to fibrosis.

1. Antigen Avoidance

• Environmental control: Relocate to a low‑exposure area, improve ventilation, use high‑efficiency particulate air (HEPA) filtration, and replace soiled bedding regularly.
• Personal protective equipment (PPE): N‑95 or higher respirators, protective clothing, and gloves during cleaning or necropsy.
• Document a “work‑free” period of 2–4 weeks; symptom improvement during this time solidifies the diagnosis.

2. Pharmacologic Therapy

• Corticosteroids: First‑line for acute and sub‑acute HP.
  • Prednisone 0.5 mg/kg/day for 2–4 weeks, then taper over 3–6 months based on response.
  • Monitor blood glucose, blood pressure, and bone density during prolonged courses.
• Immunomodulators (for steroid‑dependent or refractory disease):
  • Azathioprine 1.5–2 mg/kg/day.
  • Mycophenolate mofetil 1–2 g/day.
  • These agents have shown benefit in small case series (Kreuter et al., 2022).
• Antifibrotic agents: Nintedanib has been approved for progressive fibrotic ILD and may be considered when HP has advanced to fibrosis (INBUILD trial, 2020).

3. Supportive Care

• Supplemental oxygen for resting hypoxemia.
• Pulmonary rehabilitation to improve aerobic capacity.
• Vaccinations – annual influenza and COVID‑19 vaccines, pneumococcal immunization per CDC guidelines.

4. Follow‑up

Regular monitoring with PFTs every 3–6 months during the first year, then annually if stable. HRCT is repeated if there is clinical worsening.

Living with Zookeepers' Lung (Hypersensitivity Pneumonitis)

While the disease can be serious, many individuals maintain active careers and quality of life with proper management.

• Workplace modifications: Request rotating duties, use enclosed cages with negative pressure, and schedule cleaning tasks when fewer staff are present.
• Personal hygiene: Shower and change out of work clothes before entering home spaces; wash bedding and soft furnishings frequently.
• Medication adherence: Keep a medication calendar; set smartphone reminders for tapering steroids.
• Monitor symptoms: Use a simple diary (peak cough frequency, dyspnea score) to spot early relapse.
• Physical activity: Low‑impact exercise (walking, stationary cycling) 3–5 times weekly improves lung capacity.
• Support networks: Join occupational health programs or online communities (e.g., American Association of Zoo Veterinarians) for shared coping strategies.

Prevention

Because HP is fundamentally an exposure disease, prevention revolves around minimizing inhalation of animal antigens.

• Engineering controls: Install local exhaust ventilation at cage cleaning stations, maintain humidity < 60 %, and use dust‑free bedding materials.
• PPE protocol: Fit‑test respirators annually; train staff on correct donning/doffing.
• Routine environmental monitoring: Periodic air sampling for avian proteins or mold spores; act on positive findings promptly.
• Health surveillance: Baseline and annual PFTs for high‑risk staff; early detection enables prompt intervention.
• Education: Conduct quarterly training on HP signs, proper cleaning techniques, and the importance of reporting symptoms.

Complications

If the inciting antigen is not removed or inflammation is inadequately treated, HP can progress to irreversible lung damage.

• Fibrotic lung disease: Leads to permanent restriction, reduced DLCO, and eventual respiratory failure.
• Pulmonary hypertension: Develops in 5–10 % of chronic HP patients and worsens prognosis.
• Exacerbations: Acute worsening can mimic pneumonia and may require hospitalization.
• Secondary infections: Chronic steroid use raises risk for bacterial, fungal, or viral lung infections.
• Reduced work capacity: Advanced disease may necessitate job reassignment or early retirement.

When to Seek Emergency Care

Sources: Mayo Clinic. “Hypersensitivity Pneumonitis.” 2023; CDC. “Occupational Respiratory Diseases.” 2022; American Thoracic Society & European Respiratory Society. “Guidelines for Diagnosis and Management of HP.” 2021; Fujita et al., “Serologic Sensitization in Zoo Workers.” Occup Environ Med, 2021; Davis et al., “HLA‑DR Alleles and HP Susceptibility.” Chest, 2020; Kreuter et al., “Azathioprine in Chronic HP.” Respir Med, 2022; INBUILD Trial, Nintedanib in Progressive Fibrosing ILD, 2020.