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Updated: May 16 2021

Dog and Cat Bites

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  • summary
    • Dog and Cat Bites to the hand are common and are associated with secondary infections due to a large number of animal oral flora pathogens.
    • Diagnosis is often delayed and is confirmed with a careful history and physical examination.
    • Treatment is generally oral antibiotics but presence of soft tissue infection, abscess or tenosynovitis requires urgent irrigation and debridement. 
  • 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
    • Anatomic Location
      • upper extremity > lower extremity
  • Etiology
    • 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
      • 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
    • 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
      • rabies
        • caused by a rhabdovirus
        • common animal carriers include dogs, raccoons, bats, foxes
        • increased risk with open wounds, scratches/abrasions, mucous membranes
  • Presentation
    • 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
  • Imaging
    • Radiographs
      • indications to obtain
        • crush injuries
        • suspected fracture
        • suspected foreign body
  • Studies
    • Culture
      • indications
        • if signs of infection are present
        • routine culture not indicated
      • technique
        • deep aerobic and anaerobic culture
  • Diagnosis
    • Clinical
      • diagnosis is made with careful history and physical examination
  • Treatment
    • Nonperative
      • 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
  • Prognosis
    • Serious and fatal bites include
      • large, aggressive dogs
      • small children
      • head and neck bites
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