Updated: 4/7/2018

Dog and Cat Bites

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  • Bites by domestic animals are common
    • delayed presentation (>1week) is common
    • required care is often underestimated
  • Epidemiology
    • incidence (dog > cat > human)
      • dog bites are most common animal bites in the US (90%)
        • dog is known to victim in 90% of cases
      • cat bites are 2nd most common (10%)
      • human bites are 3rd most common
    • demographics
      • more common in males
      • more frequent at ages 2-19 years
    • location
      • upper extremity > lower extremity
  • Pathophysiology
    • mechanism
      • dog bites
        • cause crush, puncture, avulsion, tears and abrasions
        • large dogs' jaws exert >450lbs/ square inch  
        • more likely to cause structural damage to nerves, vessels, joints
      • cat bites
        • penetrate bones and joints, and cause septic arthritis and osteomyelitis
        • small, sharp teeth cause puncture wounds that seal immediately  
        • penetrate joints and flexor tendons
        • higher risk for infection than dog bites
  • Associated conditions
    • secondary bacterial infection
      • most bites do not become infected
      • risk factors for infection
        • bite to hand, foot, or major joint
        • puncture wounds or crush injuries
        • treatment delay >12h
        • age >50y
        • preexisting host disease
          • immune suppression (steroids, asplenism)
          • chronic alcoholism
          • diabetes mellitus
          • vascular disease
          • existing edema of extremity
      • microbiology
        • most infections are polymicrobial, with > 1 anerobe
        • most common isolate from both cats and dogs is Pasteurella sp. 
          • gram-negative, facultative, anaerobic, pleomorphic coccobacillus
          • inform lab about potential for Pasteurella 
            • cultures require appropriate growth media and take 1wk to grow
        • dog bites
          • Pasteurella (50% of dog bite infections)
            • Pasteurella canis
          • Staphylococcus aureus
          • Streptococcus alpha-hemolytic
          • Corynebacterium
          • anerobes (e.g. Bacteroides)
          • Capnocytophaga canimorsus
            • rare, potentially fatal (in splenectomy patients)
            • causes cellulitis, sepsis, endocarditis, meningitis, DIC, ARDS and death
            • highest mortality in immunocompromised (30-60%)
        • cat bites
          • Pasteurella (most common, 70-80% of cat bite infections)
            • Pasteurella multocida and Pasteurella septica               
            • causes intense pain, swelling in 48h
          • other organisms similar to dog bites
    • rabies
      • caused by a rhabdovirus
      • common animal carriers include dogs, raccoons, bats, foxes
      • increased risk with open wounds, scratches/abrasions, mucous membranes
  • Prognosis
    • serious and fatal bites include
      • large, aggressive dogs
      • small children
      • head and neck bites
  • History
    • important to determine
      • type of animal
      • time since injury
      • presence of comorbidities
  • Symptoms
    • pain and swelling
    • bleeding
    • signs of local or systemic sepsis
  • Physical Exam
    • evaluate depth of puncture wound and presence of crush injury
    • check for neurovascular status
    • look for joint penetration
    • important to photograph wounds
  • Radiographs
    • indications to obtain
      • crush injuries
      • suspected fracture
      • suspected foreign body
  • Culture
    • indications
      • if signs of infection are present
      • routine culture not indicated
    • technique
      • deep aerobic and anaerobic culture 
  • Noperative
    • copious irrigation, prophylactic antibiotics, tetanus toxoid, +/- rabies prophylaxis
      • copious irrigation in emergency room
        • saline (>150ml) irrigation with 18-19G needle or plastic catheter
        • use povidone-iodine solution if high risk of rabies
      • indications for antibiotics
        • cat bites
        • presentation >8h
        • immune compromised or diabetic
        • hand bite
        • deep bites
        • choice of antibiotics
          • amoxicillin/clavulanic acid effective against Pasteurella multocida
          • cefuroxime
          • ceftriaxone
      • rabies prophylaxis
        • indicated when any suspicion for rapid animal
          • suspect if unprovoked attack by animal with bizarre behavior
        • human diploid cell vaccine and human rabies immunoglobulin
      • immobilization
        • immobilize and elevate extremity
  • Operative
    • formal surgical debridement 
      • indications
        • crush or devitalized tissue
        • foreign body
        • bites to digital pulp space, nail bed, flexor tendon sheath, deep spaces of the palm, joint spaces
        • tenosynovitis
        • septic arthritis
        • abscess formation

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