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🦠 Pasteurella multocida - Complete Veterinary Science Guide

1. Overview & Classification

Species & Subspecies of Veterinary Importance

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2. Microbiology & Morphology

• Type A - Most common; respiratory disease in cattle, pigs, rabbits, cats, dogs
• Type B - Hemorrhagic septicemia in cattle and buffalo (major disease in Asia/Africa)
• Type D - Atrophic rhinitis in pigs; pneumonia
• Type E - Hemorrhagic septicemia in Africa
• Type F - Poultry, turkeys

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3. Virulence Factors

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4. Disease Syndromes in Animals (Veterinary Importance)

A. Hemorrhagic Septicemia (Cattle & Buffalo)

• Caused by capsular type B (Asia) and type E (Africa)
• Peracute to acute disease
• Signs: sudden high fever (41-42°C), salivation, lacrimation, submandibular edema, respiratory distress, death within 24 hours
• Economically the most devastating Pasteurella disease worldwide

B. Fowl Cholera (Poultry)

• Caused by type A strains
• Affects chickens, turkeys, ducks, geese
• Forms: peracute (sudden death), acute (septicemia, green diarrhea, cyanotic wattles), chronic (swollen wattles, sinuses, joints)

C. Pneumonic Pasteurellosis (Cattle, Sheep, Goats) - "Shipping Fever"

• Part of the Bovine Respiratory Disease (BRD) complex
• P. multocida type A acts as a secondary pathogen after viral infections (IBR, BVD, PI-3) or stress
• Co-pathogens: Mannheimia haemolytica, Bibersteinia trehalosi
• Signs: fever, dyspnea, coughing, nasal discharge, depression, anorexia, abnormal lung sounds
• Gross lesions: cranioventral fibrinopurulent bronchopneumonia, coagulative necrosis, fibrinous pleuritis

D. Atrophic Rhinitis (Pigs)

• Caused by toxigenic type D strains (dermonecrotoxin)
• Progressive destruction of nasal turbinate bones leading to snout deviation
• Secondary infection alongside Bordetella bronchiseptica

E. Snuffles (Rabbits)

• Chronic upper respiratory infection (rhinitis, sinusitis)
• Carrier state common; spreads through direct contact
• Can progress to pneumonia, otitis media, conjunctivitis

F. Wound Infections (Cats & Dogs)

• Normal oral flora in 70-90% of cats and 25-50% of dogs
• Transmitted through bites, scratches, or licking of open wounds
• Rapid onset (within hours): redness, swelling, pain at wound site
• Can progress to cellulitis, septic arthritis, osteomyelitis, bacteremia

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5. Pathogenesis (Step by Step)

1. COLONIZATION
   Bacteria reside as commensals in upper respiratory tract or oral cavity of carrier animals

2. STRESS / PREDISPOSING FACTORS
   Transport stress, overcrowding, viral infections, immunosuppression, malnutrition
   → Impairs mucociliary clearance and immune response

3. MUCOSAL INVASION
   Adhesins (fimbriae, OMPs, filamentous hemagglutinin) bind to respiratory epithelial cells
   Neuraminidase cleaves protective sialic acid layer

4. EVASION OF HOST DEFENSES
   Capsule blocks phagocytosis and complement attack
   Iron-acquisition proteins sustain growth in iron-limited host environment

5. LOCAL TISSUE DAMAGE
   LPS triggers cytokine storm → inflammation, fibrin deposition
   Dermonecrotoxin (type D) causes turbinate bone necrosis

6. SYSTEMIC SPREAD
   Bacteremia → septicemia → multiorgan failure (hemorrhagic septicemia in cattle/buffalo)

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6. Diagnosis

Clinical Diagnosis

• History of animal bite, stress event, or herd outbreak
• Clinical signs appropriate to the syndrome (respiratory, septicemia, wound)
• Preliminary diagnosis based on history + signs + gross necropsy findings

Laboratory Diagnosis

A. Sample Collection

B. Bacteriological Culture

• Blood agar (5% sheep blood): Smooth, greyish, non-hemolytic colonies at 24-48h
• Chocolate agar: Good growth
• MacConkey agar: No growth (important negative)
• Characteristic smell: Distinctive musty/indole-like odor

C. Key Biochemical Tests (Rapid Identification)

D. Serotyping

• Capsular typing (Carter/Rimler-Rhoades method): Hyaluronidase test for type A; acriflavine agglutination; PCR-based capsular typing
• LPS (somatic) typing (Heddleston): Gel diffusion precipitation test

E. Molecular Methods (Gold Standard for Typing)

• PCR targeting the kmt1 gene (species-specific confirmatory test)
• Multiplex PCR for capsular typing (identifies types A, B, D, E, F simultaneously)
• 16S rRNA gene sequencing for definitive species identification
• MALDI-TOF mass spectrometry - highly accurate, rapid identification increasingly used in modern diagnostic labs

F. Animal Inoculation (Pathogenicity Test)

• White mice inoculated intraperitoneally with isolated culture
• Virulent strains cause death within 24-48 hours
• Postmortem: petechial hemorrhages on serosal surfaces, congested organs

G. Serology

• ELISA: Detects antibodies in serum; useful for herd-level surveillance and vaccine efficacy studies
• Passive hemagglutination test (PHT)
• Note: Serology alone is not sufficient for definitive diagnosis

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7. Differential Diagnosis

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8. Treatment

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9. Prevention & Control

• Vaccination:
  • Hemorrhagic septicemia: Oil-adjuvanted or aluminum hydroxide-adsorbed bacterins; protective for 6-12 months
  • Fowl cholera: Live attenuated (P. multocida M-9) and killed bacterin vaccines available
  • Bovine shipping fever: Multivalent vaccines (combined with Mannheimia haemolytica)
  • No commercially available vaccine for small ruminant pasteurellosis in the US
• Management: Reduce stressors (transport, mixing animals, overcrowding, weaning)
• Metaphylaxis: Prophylactic antimicrobials in high-risk cattle at feedlot entry
• Biosecurity: Quarantine new animals; control rodents and wild birds (vectors for fowl cholera)
• Wound care: Prompt cleansing and antimicrobial treatment after animal bites

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10. Zoonotic Importance

• Cat or dog bites (cats involved in 60-80% of human cases)
• Scratches or licking of open wounds
• Rarely, respiratory transmission from heavily colonized animals

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Quick Memory Summary (MNEMONICS)

• P - Pleomorphic coccobacillus, bipolar staining
• A - Animal commensal (cats, dogs, cattle)
• S - Safety-pin appearance on Giemsa stain
• T - Types A, B, D, E, F (Carter capsular typing)
• C - Capsule = main virulence factor
• U - Urease negative (unlike Brucella)
• R - Respiratory + wound infections primary diseases
• E - Endotoxin causes hemorrhagic septicemia

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