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Updated: Dec 22 2021

Animal and Human Bites

  • Snapshot
    • A 29-year-old man presents to the emergency department 1 day after being in a fist fight at a bar. He punched his opponent in the mouth after having an argument, which resulted in a laceration of his dorsal hand. When he went home, he attempted to wash the laceration with soap and water and applied antibiotic cream. One day later, he developed swelling of the hand and pus was draining. Physical examination is notable for marked swelling in the ulnar aspect of the hand and severe tenderness over the fourth metacarpal joint, and pus is noted to be draining from the joint. Sensory examination is normal, and strength examination is limited by pain. In the emergency department, he obtained a radiograph of the hand, which did not demonstrate any acute fractures or foreign bodies. He immediately received a tetanus booster, and orthopedics was consulted for possible irrigation and drainage of the joint. Given the clinical extent of the infection, he is started on intravenous ampicillin-sulbactam.
  • Introduction
    • Definition
      • bites caused by an animal or human
        • human bites can also result from a fist hitting the person's mouth
    • Microbiology
      • general principle
        • oral flora of the biting animal (e.g., dog and human) and skin
      • animal bites
        • Pasteurella, Staphylococcus and Streptococcus species, and anaerobic bacteria
        • Bartonella henslae (leading to cat-scratch disease)
      • human bites
        • Eikenella corrodens
        • aerobic gram-positive cocci (e.g., group A Streptococcus)
        • anaerobes
  • Epidemiology
    • incidence
      • dog bites are the most common cause of an animal bite
      • cat bites are the second most common cause of an animal bite
      • human bites (e.g., an actual human bite or a clenched fist injury to a human's mouth) are considered the third leading cause of bites
    • Pathogenesis
      • Dog bites
        • crushing-type wound that can damage skin and deeper structures (e.g., muscle, tendon, bone, nerves, and vessels)
      • Human bites
        • clenched-fist injuries are most common
          • closed fist will collide the other person's teeth, which will typically affect the dorsal surface of the third and fourth metacarpophalangeal or proximal interphalangeal joint
            • this can result in joint penetration (leading to a septic joint), metacarpal fracture, and extensor tendon laceration
  • Presentation
    • Symptoms/physical exam
      • dog bites
        • range from
          • minor wounds (e.g., scratches and abrasions)
          • major wounds (e.g., deep open lacerations, deep puncture wounds, tissue avulsions, and crush injuries)
      • cat bites
        • typically affecting the upper extremities and face (especially cat scratches)
      • human clenched-fist injury
        • skin breaks over the knuckles
      • general
        • fever
        • erythema and swelling
        • tenderness
        • purulent drainage
        • lymphangitis
  • Imaging
    • Radiography of the involved body part (e.g., hand)
      • indication
        • in wounds near joints to evaluate for fractures and foreign bodies (e.g., embedded teeth)
  • Studies
    • Wound and blood cultures (aerobic and anaerobic)
      • indication
        • prior to antibiotic treatment in patients with an infected wound and signs of systemic infection
  • Treatment
    • Conservative
      • wound cleaning (e.g., wound irrigation and debridement of devitalized tissue)
        • indication
          • the initial step in managing an animal or human bite
    • Medical
      • empiric antibiotic treatment
        • indication
          • deep puncture wounds
          • wounds associated with crush injury
          • wounds with venous and/or lymphatic impairment
          • wounds involving the hand, genitalia, face, and wounds that are close to bone or joints (e.g., such as in the hand)
          • wounds that require closure
          • wounds in patients who
            • are immunocompromised
            • impaired or have absent spleen function
            • diabetes
        • medications
          • ampicillin-sulbactam (intravenous)
          • amoxicillin-clavulanate (oral)
          • clindamycin + ciprofloxacin
          • azithromycin (cat scratch disease)
      • tetanus prophylaxis
        • indication
          • clean and minor wounds
            • if received < 3 doses
            • if unknown immunization status
            • if the last dose is given ≥ 10 years
          • all other wounds
            • if received < 3 doses
            • if unknown immunization status
            • if the last dose is given ≥ 5 years
        • comment
          • human tetanus immunoglobulin is only given if the wound is not clean or minor and
            • if received < 3 doses or
            • if unknown immunization status
      • rabies prophylaxis
        • indication
          • when an animal with rabies causes an open wound or breaks the mucous membrane of the human
        • comments
          • not always possible to determine if the animal has rabies; thus, administration of rabies prophylaxis is dependent on the likelihood that exposure occurred
    • Operative
      • primary closure
        • indication
          • in clinically uninfected, the wound is < 12 hours old (or < 24 hours old in facial wounds) and wound not located in the hand or foot
        • comments
          • can be closed in simple wounds after a dog bite
      • delayed primary closure
        • indication
          • performed in wounds that are at high risk of developing an infection, which includes
            • human and cat bites (except in the face)
              • most are left to heal by secondary intention
            • crush injuries
            • puncture wounds
            • immunocompromised (e.g., HIV, asplenia/impaired spleen function, and diabetes)
  • Complications
    • Septic arthritis
    • Osteomyelitis
    • Deep soft tissue infection
  • Prognosis
    • Excellent in patients who promptly seek medical attention
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