Etiology
As the primary purposes of teeth and the jaw are the killing of prey, mastication of food, and defense, bite injuries are particularly efficient at causing tissue injury.
The bacteriology of infected animal wounds has been well studied. Pasteurella species such as P multocida and P canis are the most commonly isolated.[14][15] The next most commonly identified bacteria are Streptococcus, Staphylococcus, Moraxella, Corynebacterium, and Neisseria species.[14] Less common but potentially invasive organisms include Bergeyella zoohelcum, Capnocytophagacanimorsus, Blastomyces dermatitidis, and Bartonella hensalae.[14][16]
The most common organisms found in infected human bites are Streptococcus anginosis, Staphylococcus aureus, Eikenella corrodens, Fusobacterium, and Prevotella species.[14][17] Beta-lactamase-producing bacteria may be detected from human bite infections.[17]
Other diseases transmissible to humans by bites include rabies and animal-specific diseases such as hepatitis B and HIV from humans, herpes B virus from nonhuman primates, and rat bite fever (Streptobacillus or Streptococcus mitis).[18] In addition, bite wounds are prone to tetanus infection, and tetanus is a well-recognized complication. See Tetanus.
Pathophysiology
The pathophysiology is related to the animal type, specific microorganisms deposited in the wound, and anatomic location. In addition to the microbial flora resident in the mouth of the biting animal, pathogens may also originate from the skin of the victim, or the environment.
Dogs can exert >450 pounds per square inch of pressure with their jaws, causing significant crush injury and tissue devitalization, in addition to laceration, puncture, and avulsion (tearing away of tissue) injury.[19][20] Cats have weaker biting force than dogs. They have thin, sharp teeth; 85% of cat bite wounds are puncture wounds, which inoculate organisms deep into the tissue.[15] Injuries to the clenched fist can be particularly serious. Due to the high forces involved and thin skin, bites to the fist can lead to tendon tear, joint disruption, or fracture. Mortality from mammal attacks is uncommon.[4][9] The major cause of death from a dog attack is exsanguination following carotid trauma, in children <10 years old.[21]
Human bite injuries typically involve wounds from fist fights, where the fist engages the teeth and mouth. Occlusional bites are another common type. These injuries typically occur in abusive and/or drug- or alcohol-laden environments, but some bites relate to sports and sexual activity. Fist fight injuries are often small, but may be quite deep over the metacarpophalangeal joints of the dominant hand. Occlusional bites are found anywhere on the body, but females often are more likely bitten on the breast, genitalia, leg, and arm, whereas men tend to receive bite injuries on the hand, arm, or shoulder.[22]
Many wounds become infected. The majority of these infections are polymicrobial with a median of 5 isolates per wound. Over 50% of cat and dog bites involve mixed aerobic and anaerobic bacteria.[23] An estimated 3% to 18% of dog bites become infected, and the median time from bite to infection is 24 hours.[6][15] Due to the high rate of puncture wounds, infection rates after cat bites may be as high as 50%, with a median time of 12 hours before first signs of infection.[15][24] Human bites have an overall infection rate ranging from 10% to 50%.[22]
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