Pasteurellosis (Soft Tissue Infections) (Pasteurella multocida)
Overview
Plain-Language Overview
Pasteurellosis (Soft Tissue Infections) (Pasteurella multocida) is an infection that usually occurs after an animal bite or scratch, commonly from cats or dogs. It affects the skin and soft tissues, causing redness, swelling, and pain around the wound. This infection can spread quickly and may lead to more serious problems if not treated. The bacteria involved, Pasteurella multocida, are part of the normal flora in many animals but can cause illness in humans. Symptoms often develop within hours to a day after the injury. The infection mainly impacts the immune system’s ability to control bacterial growth in the affected area. Early recognition of the infection is important to prevent complications.
Clinical Definition
Pasteurellosis (Soft Tissue Infections) (Pasteurella multocida) is a bacterial infection characterized by acute soft tissue inflammation following animal bites or scratches, primarily from cats and dogs. The core pathology involves rapid bacterial proliferation in the subcutaneous tissues, leading to cellulitis, abscess formation, and sometimes septic arthritis or osteomyelitis. The causative agent, Pasteurella multocida, is a gram-negative coccobacillus that is part of the normal oral flora of many animals. The infection is clinically significant due to its rapid onset, potential for systemic spread, and risk of complications such as sepsis or chronic infection if untreated. Patients typically present with painful erythema, swelling, and purulent discharge at the site of injury within 24 hours. Immunocompromised individuals and those with prosthetic devices are at higher risk for severe disease. Prompt diagnosis and management are critical to prevent morbidity.
Inciting Event
Cat or dog bite or scratch is the primary trigger for Pasteurella multocida soft tissue infection.
Direct inoculation of bacteria into skin or subcutaneous tissue through animal-inflicted trauma initiates disease.
Handling or close contact with animals without visible trauma can occasionally lead to infection via minor unnoticed skin breaks.
Latency Period
Symptoms typically develop within 24 hours after animal bite or scratch.
Rapid onset of cellulitis usually occurs within 12 to 24 hours post-exposure.
Delayed presentation beyond 48 hours is less common but may occur in immunocompromised patients.
Diagnostic Delay
Failure to elicit history of animal bite or scratch often leads to missed diagnosis.
Misattribution to common cellulitis pathogens such as Staphylococcus aureus delays targeted therapy.
Lack of awareness of Pasteurella multocida as a cause of soft tissue infection contributes to diagnostic delay.
Initial empirical treatment without coverage for Pasteurella may result in poor clinical response and delayed recognition.
Clinical Presentation
Signs & Symptoms
Rapid onset of pain, swelling, and redness within 24 hours after animal bite or scratch.
Fever and malaise may accompany localized infection.
Purulent drainage or serosanguinous fluid from the wound.
Tender regional lymphadenopathy and lymphangitic streaking may occur.
Severe infections can cause systemic signs such as hypotension and tachycardia.
History of Present Illness
Acute onset of localized pain, swelling, and erythema at the site of animal bite or scratch.
Rapid progression of cellulitis with possible purulent discharge within 24 hours of injury.
Fever and regional lymphadenopathy may accompany local signs of infection.
In severe cases, development of abscess or necrotizing infection can occur if untreated.
Past Medical History
History of diabetes mellitus or immunosuppression increases risk of severe infection.
Previous animal bites or soft tissue infections may predispose to recurrent Pasteurella infections.
Chronic skin conditions or ulcers provide portals of entry for bacteria.
Prior antibiotic use may alter clinical presentation and complicate diagnosis.
Family History
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Physical Exam Findings
Localized erythema, swelling, and tenderness at the site of animal bite or scratch.
Warmth and induration over the affected soft tissue indicating inflammation.
Possible purulent discharge or abscess formation in advanced infections.
Lymphangitis or regional lymphadenopathy may be present in spreading infection.
In severe cases, signs of cellulitis or necrotizing fasciitis can be observed.
Diagnostic Workup
Diagnostic Criteria
Diagnosis of soft tissue infection caused by Pasteurella multocida is established by clinical history of recent animal bite or scratch combined with rapid onset of localized cellulitis or abscess. Definitive diagnosis requires isolation of Pasteurella multocida from wound cultures or aspirated pus, which shows characteristic gram-negative coccobacilli on Gram stain. Blood cultures may be positive in systemic infection. Imaging such as X-ray or MRI can be used to assess for deeper involvement like osteomyelitis. The diagnosis is confirmed by microbiological identification using culture and biochemical testing or molecular methods.
Pathophysiology
Key Mechanisms
Inoculation of Pasteurella multocida into soft tissue via animal bites or scratches initiates infection.
Bacterial virulence factors including a polysaccharide capsule and endotoxins promote local tissue inflammation and abscess formation.
Rapid bacterial proliferation leads to acute cellulitis characterized by erythema, swelling, and pain.
Host immune response with neutrophil infiltration causes pus formation and tissue necrosis in severe cases.
Potential hematogenous spread can result in systemic infection or septic arthritis in immunocompromised hosts.
| Involvement | Details |
|---|---|
| Organs | Skin is the primary organ affected in Pasteurellosis, presenting with erythema, swelling, and pain at the infection site. |
Lymph nodes may become enlarged and tender due to regional lymphadenitis secondary to bacterial spread. | |
| Tissues | Subcutaneous tissue is commonly involved in soft tissue infections caused by Pasteurella multocida, leading to cellulitis and abscess formation. |
Skin serves as the initial barrier breached by animal bites or scratches that introduce the pathogen. | |
| Cells | Neutrophils are the primary immune cells that phagocytose and kill Pasteurella multocida during soft tissue infection. |
Macrophages contribute to bacterial clearance and release pro-inflammatory cytokines that mediate tissue inflammation. | |
| Chemical Mediators | Interleukin-1 (IL-1) and Tumor Necrosis Factor-alpha (TNF-α) are key cytokines driving local inflammation and systemic symptoms in infection. |
Reactive oxygen species (ROS) produced by activated neutrophils contribute to bacterial killing and tissue damage. |
Treatments
Pharmacological Treatments
Amoxicillin-clavulanate
- Mechanism:
Inhibits bacterial cell wall synthesis and beta-lactamase enzymes, effective against Pasteurella multocida
- Side effects:
Allergic reactions
Gastrointestinal upset
Rash
- Clinical role:
First-line
Doxycycline
- Mechanism:
Inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit
- Side effects:
Photosensitivity
Gastrointestinal upset
Tooth discoloration in children
- Clinical role:
Second-line
Ciprofloxacin
- Mechanism:
Inhibits bacterial DNA gyrase and topoisomerase IV, preventing DNA replication
- Side effects:
Tendonitis
Gastrointestinal upset
QT prolongation
- Clinical role:
Second-line
Non-pharmacological Treatments
Prompt wound cleaning and irrigation to reduce bacterial load and prevent infection progression.
Surgical debridement of necrotic tissue in severe or deep soft tissue infections.
Tetanus prophylaxis as indicated based on immunization status and wound characteristics.
Prevention
Pharmacological Prevention
Prophylactic amoxicillin-clavulanate after high-risk animal bites to prevent infection.
Tetanus toxoid booster if indicated based on immunization status.
Rabies post-exposure prophylaxis when animal bite risk is present.
Non-pharmacological Prevention
Immediate and thorough wound cleansing with soap and water after animal bites or scratches.
Avoidance of contact with stray or wild animals to reduce exposure risk.
Proper animal vaccination and control to prevent transmission of Pasteurella multocida.
Use of protective gloves when handling animals or cleaning wounds.
Outcome & Complications
Complications
Abscess formation requiring surgical drainage.
Sepsis and systemic inflammatory response syndrome from bacteremia.
Osteomyelitis if infection spreads to underlying bone.
Septic arthritis if joint involvement occurs.
Necrotizing fasciitis as a rare but life-threatening complication.
| Short-term Sequelae | Long-term Sequelae |
|---|---|
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Differential Diagnoses
Pasteurellosis (Soft Tissue Infections) (Pasteurella multocida) versus Staphylococcal Soft Tissue Infection
Pasteurellosis (Soft Tissue Infections) (Pasteurella multocida) | Staphylococcal Soft Tissue Infection |
|---|---|
Infection caused by Pasteurella multocida | Infection caused by Staphylococcus aureus |
Typically follows animal bite or scratch, especially cats or dogs | Often occurs without animal bite or scratch history |
Requires penicillin or amoxicillin-clavulanate due to beta-lactamase production | Responds well to anti-staphylococcal agents like nafcillin |
Pasteurellosis (Soft Tissue Infections) (Pasteurella multocida) versus Eikenella corrodens Soft Tissue Infection
Pasteurellosis (Soft Tissue Infections) (Pasteurella multocida) | Eikenella corrodens Soft Tissue Infection |
|---|---|
Infection caused by Pasteurella multocida, a facultative anaerobic gram-negative coccobacillus | Infection caused by Eikenella corrodens, a facultative anaerobe |
Associated with animal bites or scratches | Associated with human bite wounds or fist fights |
Sensitive to penicillin and amoxicillin-clavulanate | Resistant to clindamycin and metronidazole |
Pasteurellosis (Soft Tissue Infections) (Pasteurella multocida) versus Capnocytophaga canimorsus Infection
Pasteurellosis (Soft Tissue Infections) (Pasteurella multocida) | Capnocytophaga canimorsus Infection |
|---|---|
Infection caused by Pasteurella multocida, a gram-negative coccobacillus | Infection caused by Capnocytophaga canimorsus, a gram-negative rod |
Follows cat or dog bites, often in immunocompetent hosts | Typically follows dog bites, especially in immunocompromised hosts |
Usually causes localized soft tissue infection with cellulitis and abscess | Can cause fulminant sepsis and disseminated intravascular coagulation |
Pasteurellosis (Soft Tissue Infections) (Pasteurella multocida) versus Anaerobic Soft Tissue Infection (e.g., Bacteroides fragilis)
Pasteurellosis (Soft Tissue Infections) (Pasteurella multocida) | Anaerobic Soft Tissue Infection (e.g., Bacteroides fragilis) |
|---|---|
Infection caused by facultative anaerobic Pasteurella multocida | Infection caused by anaerobic gram-negative rods like Bacteroides fragilis |
Associated with animal bite or scratch wounds | Often associated with deep puncture wounds or ischemic tissue |
Responds to penicillin or amoxicillin-clavulanate | Requires metronidazole or beta-lactam/beta-lactamase inhibitor combinations |