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Psittacosis / Ornithosis in Animals


Introduction

Psittacosis (in psittacine birds) or Ornithosis (in non-psittacine birds) is a contagious zoonotic disease caused by Chlamydia psittaci. It affects a wide range of avian species and can also infect mammals, including humans. The disease is characterized by respiratory, gastrointestinal, and systemic signs, and is of significant veterinary and public health importance.

Etiology
Causative Agent

The disease is caused by Chlamydia psittaci, an obligate intracellular bacterium.

Organism Characteristics
  • Gram-negative-like bacterium
  • Obligate intracellular lifecycle
  • Two forms: elementary body (infectious) and reticulate body (replicative)
  • Can persist in birds as a latent infection
Epidemiology
Species Affected
  • Psittacine birds (parrots, parakeets, macaws)
  • Poultry (chickens, turkeys, ducks)
  • Pigeons and other wild birds
  • Occasionally mammals (including humans)
Transmission
  • Inhalation of aerosolized contaminated dust (primary route)
  • Ingestion of contaminated feed or water
  • Direct contact with infected birds or secretions
Sources of Infection
  • Feces
  • Respiratory secretions
  • Feather dust
Risk Factors
  • Stress (transport, overcrowding)
  • Poor ventilation
  • Mixing of birds from different sources
  • Carrier birds shedding intermittently
Pathogenesis
Entry and Initial Infection

The organism enters primarily via the respiratory tract and infects epithelial cells and macrophages.

Systemic Spread
  • Dissemination via bloodstream (bacteremia)
  • Infection of multiple organs (liver, spleen, lungs)
Cellular Effects
  • Intracellular replication leads to cell damage and inflammation
  • Granulomatous lesions in affected organs
Clinical Signs
General Signs
  • Depression
  • Anorexia
  • Weight loss
Respiratory Signs
  • Nasal discharge
  • Dyspnea
  • Sneezing
Gastrointestinal Signs
  • Diarrhea (often greenish due to bile pigments)
  • Dehydration
Other Signs
  • Conjunctivitis
  • Reduced egg production in poultry
Subclinical Infection
  • Many birds remain asymptomatic carriers
  • Shedding may increase during stress
Summary for Practitioners

Psittacosis should be suspected in birds with respiratory and systemic illness, especially when zoonotic risk is a concern or when birds are from mixed or stressed populations.

Postmortem Findings
Gross Lesions
  • Hepatomegaly (enlarged liver)
  • Splenomegaly (enlarged spleen)
  • Airsacculitis
  • Fibrinous exudates in body cavities
Microscopic Lesions
  • Necrosis and inflammation in liver and spleen
  • Intracellular inclusions in infected cells
  • Granulomatous inflammation
Diagnosis
Clinical Diagnosis

Based on clinical signs, species affected, and history of exposure.

Laboratory Diagnosis
  • PCR for detection of Chlamydia psittaci DNA
  • Serology (ELISA, complement fixation)
  • Cytology demonstrating intracellular inclusions
Differential Diagnosis
  • Avian influenza
  • Newcastle disease
  • Mycoplasmosis
  • Bacterial respiratory infections
Summary for Practitioners

Laboratory confirmation is essential due to zoonotic risk and similarity to other avian respiratory diseases.

Treatment
Antibiotic Therapy
  • Tetracyclines (e.g., doxycycline) are the treatment of choice
  • Prolonged treatment (often 2–4 weeks) is required
Supportive Care
  • Fluid therapy
  • Improved nutrition
  • Reduction of stress
Summary for Practitioners

Treatment must be prolonged and carefully managed. Infected birds should be isolated to prevent spread.

Control and Prevention
Biosecurity
  • Quarantine new birds
  • Maintain good hygiene and ventilation
  • Avoid overcrowding
Management Practices
  • Regular health monitoring
  • Minimize stress factors
  • Proper cleaning and disinfection of cages and equipment
Public Health Measures
  • Use protective equipment when handling birds
  • Educate handlers about zoonotic risks
Summary for Practitioners

Control focuses on biosecurity, proper management, and minimizing zoonotic transmission risks.

Zoonotic Importance

Chlamydia psittaci is highly zoonotic and can cause psittacosis in humans, characterized by flu-like illness and pneumonia. Occupational exposure (veterinarians, bird handlers) is a major risk.

Economic Importance

Psittacosis leads to economic losses due to decreased productivity, treatment costs, trade restrictions, and public health implications.

Summary

Psittacosis/Ornithosis is a zoonotic disease of birds caused by Chlamydia psittaci, characterized by respiratory and systemic illness. Effective management requires prompt diagnosis, antibiotic treatment, and strict biosecurity measures.