Animal Bites

Animal bites are common, potentially limb-threatening injuries that combine mechanical tissue damage with bacterial inoculation. They account for up to 1% of emergency presentations worldwide, with dogs responsible for the large majority and cats for a smaller but disproportionately infective share. School-age children are bitten most often, frequently by a familiar animal.

• Dogs (around 80-90%): Powerful jaws produce crush, tear and avulsion injuries; deep structural damage and paediatric facial fractures are possible, but infection rates are comparatively low.
• Cats (around 5-15%): Fine sharp teeth inoculate bacteria deep into closed spaces; despite small entry wounds, infection rates reach 30-50%.
• High-risk hosts: Asplenic, cirrhotic, diabetic and immunocompromised patients face disproportionately severe infections regardless of wound size.

Bite infections are driven by the oral flora of the biting animal inoculated directly into tissue. Infected wounds are typically polymicrobial, with a median of around 5 organisms per culture (Talan, NEJM 1999).

• Pasteurella species are the hallmark: P. canis predominates in dogs and P. multocida in cats. Pasteurella produces a characteristically rapid (often under 24 hours) cellulitis with intense pain and serosanguinous discharge.
• Aerobic co-pathogens: streptococci, staphylococci, Moraxella, Neisseria.
• Anaerobes: Fusobacterium, Bacteroides, Porphyromonas, Prevotella - common in deep wounds.
• Capnocytophaga canimorsus: a fastidious Gram-negative rod from dog/cat saliva that causes fulminant sepsis (DIC, shock, purpura) in asplenic and immunocompromised hosts, with around 30% mortality.
• Mechanical factor: cat punctures seal bacteria within closed tissue planes (flexor sheath, joint), converting a tiny wound into a deep-space infection.

• History: Animal type and provocation, time since injury, tetanus and rabies risk (region, vaccination), and host factors (asplenia, immunosuppression, diabetes, cirrhosis).
• Inspection: Wound type and depth, devitalised tissue, contamination, proximity to joints/tendons.
• Neurovascular and tendon exam: Document distal sensation, perfusion and active tendon function before and after exploration.
• Signs of established infection: Spreading erythema, lymphangitis, abscess, fever; in the digit look for the four Kanavel signs of flexor tenosynovitis (fusiform swelling, semi-flexed posture, tenderness along the sheath, pain on passive extension).

• Prophylaxis: Indicated for all cat bites, deep dog bites, hand bites, and immunocompromised hosts. Duration: 3-5 days.
• Treatment: Indicated for established infection. Duration: 7-14 days. IV if systemic signs.

• Septic Arthritis: From direct inoculation. Destroys cartilage rapidly (chondrolysis). requiring serial washouts.
• Osteomyelitis: If bone is bitten.
• Tenosynovitis: Pyogenic flexor tenosynovitis requires urgent drainage.
• Rabies: Almost universally fatal once symptomatic. Globally over 99% of human rabies is dog-transmitted; bat lyssaviruses (for example Australian and European Bat Lyssavirus) require the same post-exposure protocol.
• Post-Traumatic Stress Disorder (PTSD): Common after dog attacks.

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Acute Phase (Days 1-7)

• Splinting: Position of safety (Intrinsic plus) for hand bites to prevent contracture
  • MCP joints flexed 70-90°
  • IP joints extended
  • Wrist in neutral to slight extension
• Edema Control: Elevation above heart level is critical
  • Compressive dressing (non-circumferential)
  • Active finger pumping exercises when permitted
• Wound Care: Daily dressing changes to monitor for spreading infection

Subacute Phase (Weeks 1-4)

• Mobilization: Early controlled mobilization once infection cleared
  • Active range of motion within splint
  • Passive range if tendon repair performed (modified Duran protocol)
• Scar Management: Silicone sheets, massage once epithelialized
• Strengthening: Gradual isometric then isotonic exercises

Late Phase (Weeks 4-12)

• Return to Function: Occupation-specific rehabilitation
• Desensitization: For painful scars or hypersensitivity
• Contracture Prevention: Night splinting if MCP or PIP stiffness developing

• Infection Rate: With proper debridement and antibiotics, infection rate is low (less than 5% for dogs).
• Function: Depends on structural injury. Nerve repairs in dirty wounds have poorer outcomes.
• Cosmesis: Scar revision may be needed later.

• Primary closure of dog bites: Historically all bites were left open. Modern RCT evidence (Paschos, Injury 2013) shows that thoroughly irrigated, early-presenting, non-puncture dog-bite lacerations - especially of the face - can be closed primarily with better cosmesis and no excess infection. The hand and puncture wounds remain off-limits to primary closure.
• Routine antibiotic prophylaxis for low-risk dog bites: The Cochrane review found no proven benefit of prophylaxis for general cat or dog bites, only for hand bites and human bites. Practice nonetheless leans toward prophylaxis in many high-risk wounds and hosts because the consequences of hand-space infection are severe; this gap between trial evidence and pragmatic practice is a legitimate viva discussion point.
• Cephalosporin monotherapy: First-generation cephalosporins (cephalexin) have unreliable activity against Pasteurella multocida and are inadequate as sole therapy; this is a recurring exam trap and a real-world prescribing error.
• Irrigation pressure and additives: Extrapolating from the FLOW trial, high-pressure pulsatile lavage offers no benefit over low-pressure saline and soap additives may be harmful; copious low-pressure normal saline is preferred.
• Foreign-body imaging: Radiolucent tooth fragments and small radiolucent debris are easily missed on plain films; the role of ultrasound or CT for occult foreign bodies in persistently infected bites is evolving.

Global Epidemiology

• Burden: Mammalian bites account for up to 1% of all emergency department visits worldwide (per the Cochrane review of mammalian-bite prophylaxis).
• Species mix: Dogs cause roughly 80-90% of bites globally; cats 5-15%; humans and other species the remainder. School-age children make up nearly half of those bitten.
• Infection risk: Dog-bite lacerations have lower infection rates (commonly cited 5-20%) than cat-bite punctures (30-50%), reflecting deep inoculation in a closed space rather than wide tearing.
• Rabies: WHO estimates roughly 59,000 human rabies deaths per year, over 95% in Asia and Africa and over 99% transmitted by dogs - in stark contrast to rabies-free regions where the chief concern is wound infection.

Side-by-Side Guideline Comparison

Registry and Surveillance Notes

• Animal bites are notifiable in many jurisdictions chiefly for rabies surveillance, not for orthopaedic outcomes; there is no dedicated international bite-injury implant registry.
• Rabies-endemic regions rely on WHO and national surveillance to guide post-exposure prophylaxis supply, whereas rabies-free regions (parts of Oceania, Western Europe, the UK) focus reporting on dangerous-animal legislation.

Rabies and Bat Lyssavirus

• Rabies-free vs endemic regions: In rabies-free countries the dominant risk from a domestic dog or cat bite is bacterial infection, not rabies; in endemic regions every unprovoked bite should trigger a WHO category-based PEP assessment.
• Lyssaviruses in bats: Several regions harbour rabies-related lyssaviruses in bats (for example Australian Bat Lyssavirus, European Bat Lyssavirus). Any bat bite, scratch or mucous-membrane exposure should be managed as a potential rabies exposure regardless of the local terrestrial-rabies status.
• PEP principles (WHO): Immediate copious wound washing, rabies vaccine series, and rabies immunoglobulin infiltrated at the wound for category III exposures or immunocompromised hosts. Symptomatic rabies is almost universally fatal.

Tetanus Prophylaxis (Global Principle)

High- vs Limited-Resource Practice Variation

• High-resource settings: Ready access to co-amoxiclav, theatre time for washout, microbiology with anaerobic culture, and reliable rabies vaccine/immunoglobulin stocks.
• Limited-resource settings: Rabies-endemic with potential vaccine/immunoglobulin shortages; the WHO emphasises immediate, thorough wound washing with soap and water as the single most cost-effective intervention to reduce rabies and bacterial infection where definitive prophylaxis is constrained.