Pasteurellosis in Animals
Introduction
Pasteurellosis is a group of infectious diseases in animals caused by bacteria of the genus Pasteurella and closely related organisms such as Mannheimia and Bibersteinia. It commonly affects the respiratory system, leading to pneumonia, but may also cause septicemia and other systemic infections. The disease is of major importance in livestock production, particularly in cattle, sheep, goats, and poultry.
Etiology
Causative Agents
- Pasteurella multocida
- Mannheimia haemolytica (formerly Pasteurella haemolytica)
- Bibersteinia trehalosi
Characteristics
- Gram-negative, non-spore forming coccobacilli
- Often part of normal flora of the upper respiratory tract
- Opportunistic pathogens that cause disease under stress conditions
Epidemiology
Distribution
Pasteurellosis occurs worldwide and is commonly associated with intensive livestock production systems.
Species Affected
- Cattle (shipping fever complex)
- Sheep and goats
- Poultry (fowl cholera)
- Pigs and companion animals
Transmission
- Direct contact with infected animals
- Aerosol transmission via respiratory secretions
- Stress-induced proliferation of resident bacteria
Risk Factors
- Transport stress ("shipping fever")
- Overcrowding
- Poor ventilation
- Concurrent viral infections (e.g., respiratory viruses)
Pathogenesis
Mechanism of Disease
Under stress or immunosuppression, bacteria multiply in the upper respiratory tract and invade the lungs. Toxins and inflammatory responses lead to lung damage.
Virulence Factors
- Leukotoxins (especially in Mannheimia haemolytica)
- Capsule that resists phagocytosis
- Endotoxins that trigger inflammation
Clinical Signs
Respiratory Form
- Fever
- Coughing
- Nasal discharge
- Difficulty breathing (dyspnea)
- Depression and reduced appetite
Septicemic Form
- Sudden onset
- High fever
- Rapid death (especially in young animals)
Species-Specific Manifestations
- Cattle: shipping fever pneumonia
- Sheep/goats: pneumonia and septicemia
- Poultry: fowl cholera (acute septicemia)
Postmortem Findings
Gross Lesions
- Consolidated lungs (firm, dark red areas)
- Fibrinous pneumonia and pleuritis
- Fluid in thoracic cavity
- Hemorrhages in severe cases
Microscopic Lesions
- Inflammation of lung tissue
- Necrosis and infiltration of inflammatory cells
Diagnosis
Clinical Diagnosis
Based on respiratory signs, herd history, and stress-related outbreaks.
Laboratory Diagnosis
- Bacterial culture from nasal swabs or lung tissue
- PCR for identification of specific pathogens
- Serological testing
Differential Diagnosis
- Viral respiratory diseases (e.g., IBR, BRSV)
- Mycoplasma infections
- Tuberculosis
Treatment
Antibiotic Therapy
- Broad-spectrum antibiotics (e.g., tetracyclines, macrolides)
- Selection based on sensitivity testing
Supportive Care
- Anti-inflammatory drugs
- Fluid therapy
- Improved ventilation and reduced stress
Control and Prevention
Management Practices
- Reduce stress during transport and handling
- Ensure proper ventilation
- Avoid overcrowding
Vaccination
- Vaccines available against Mannheimia haemolytica and Pasteurella multocida
- Used in high-risk populations
Biosecurity
- Isolate affected animals
- Control introduction of new animals
Zoonotic Importance
Some species of Pasteurella, particularly Pasteurella multocida, can infect humans through animal bites or scratches, causing localized infections.
Economic Importance
Pasteurellosis leads to significant economic losses due to reduced growth, treatment costs, and mortality, especially in feedlot and intensive production systems.
Summary
Pasteurellosis is a common bacterial disease associated with respiratory infections in animals, often triggered by stress and environmental factors. Effective control relies on good management, vaccination, and early treatment.
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