mammal bite

Epidemiology

• dog bites account for 70-90% of animal bites
• more than 1/2 of victims are children
• cat bites account for 5-20% of bites
  • higher incidence of infection than dog bites
  • more common in women
• human & rodent bites comprise majority of other animal bites

Pathology

• bite wounds usually result in polymicrobial infections
  • aerobic & anaerobic bacteria originate from animal's oral flora, victim's skin & surrounding environment
• cat bites are more likely to become infected than dog bites

History

• regarding the animal
  • type of animal
  • relationship of animal to victim
  • circumstance of bite (provoked vs unprovoked)
  • time & location of incidence
  • vaccination & health status of animal
  • current location of the animal
• regarding the victim
  • tetanus immunization status
  • first aid measures
  • history of immunocompromise, splenectomy
  • symptoms of musculoskeletal, neurologic, lymphatic or vascular compromise

Clinical manifestations

• extremities involved in 75% of cases
• head & neck injuries are next most common
• key signs
  • hematoma
  • motor weakness
  • decreased capillary refill
  • decreased sensation
  • diminished range of motion
  • edema
  • evidence of crush injury or devitalized tissue
  • cellulitis or purulent wound drainage
  • loss of function
• complications may arise from
  • skull penetration following a bite to the cranium in a small child
  • bites over a joint
  • puncture wounds
  • lip & face bites in children
• high risk bites indicating antibiotic therapy
  • all human bites (highest risk of infection)
  • all cat bites
  • hand & foot wounds
  • wound surgically debrided
  • puncture wounds
  • wounds involving joints, ligaments, tendons or bones
  • bites in immunocompromised individuals
    • primary immunologic disorder
    • HIV
    • chronic alcoholism
    • asplenism
    • diabetes mellitus
    • prosthetic valves or joints
    • immunosuppressive therapy
• low risk wounds include lacerations of the face, extremities & body

Laboratory

• generally laboratory testing is not indicated
• wound & blood cultures in immunocompromised host, evidence of abscess, severe cellulitis, devitalized tissue, sepsis, or failure of empiric antibiotics
• gram stain on fresh uninfected wounds correlated poorly with subsequent infections

Radiology

• plain radiographs
  • bony penetration suspected
  • deep bites
  • puncture wounds
  • human bites
• MRI or CT may also be indicated

Complications

• neurovascular damage
• infection
  • bony or joint penetration with infection
    • osteomyelitis
    • septic bursitis
  • cellulitis
  • septic shock
  • meningitis & cerebral abscess
  • prosthetic valve & joint infection
  • organisms secondary to human bites
    • Staphylococcal species
    • Streptococcal species
    • Eikenella corrodens
    • Haemophilus species
    • oral anaerobes
      • Prevotella species
      • Porphyromonas species
  • organisms secondary to other animal bites
    • Staphylococcal species, including MRSA
    • Streptococcal species
    • Pasteurella canis & Pasteurella multocida
    • Capnocytophaga canimorsus
    • other aerobic & anaerobic bacteria
      • Bacteroides, Porphyromonas, Fusobacterium
• compartment syndrome
• musculotendinous injury
• severe crush injury
• fistulous tracts
• scarring & disfiguration

Management

• wound care
  • inspect for neurovascular & muscle integrity
  • debride & irrigate
    • normal saline
    • 1% povidone-iodine
    • 20% soap & water or ethyl alcohol for at least 10 minutes followed by 1% benalkonium chloride if rabies is suspected, rinse with normal saline
  • generally delayed closure of wound is prudent
    • especially if bite involves the head, hands, or feet, crush injury or signs of edema
    • facial wounds may be exception
  • elevation of extremity
• empiric antibiotic therapy
  • prophylactic antibiotics for
    • wounds on the hand or near a joint
    • wounds on face or genitalia
    • moderate or severe wounds, deep puncture wounds
    • crush injury
    • wounds associated with edema
    • immunocompromised patients
  • 3-5 days prophylactic antibiotics if no overt signs of infection
  • of no benefit; may reduce risk of wound infection
  • all infected bites
  • all human bites
    • ampicillin sulbactam (Unasyn)
    • amoxicillin-clavulanate (Augmentin)
    • cefoxitin or cefotetan
    • nafcillin IV followed by oral dicloxacillin
    • if allergic to penicillin
      • clindamycin & moxifloxacin or levofloxacin & metronidazole
      • tetracycline
    • also see clenched fist injury
  • cat bites
    • amoxicillin clavulanate (Augmentin) TID or ampicillin sulbactam (Unasyn)
    • nafcillin followed by dicloxacillin, then penicillin
  • dog bites
    • amoxicillin clavulanate (Augmentin) TID or ampicillin sulbactam (Unasyn)
    • nafcillin followed by dicloxacillin or cefazolin followed by cephalexin
  • if MRSA is suspected
    • amoxicillin clavulanate TID or ampicillin sulbactam plus vancomycin
  • if penicillin allergy
    • Bactrim, doxycycline, or minocycline (MRSA, Pasteurella) plus clindamycin (MRSA, Streptoccus, anaerobes)
• hospitalize if:
  • fever
  • sepsis
  • spreading cellulitis
  • severe edema
  • crush injury
  • loss of function
  • immunocompromised patient
  • likely to be non-compliant
• tetanus prophylaxis
  • tetanus toxoid 0.5 cc IM
    • high risk wound, no booster within 5 years
    • low risk wound, no booster within 10 years
    • no prior immunization or immunization status unknown
  • tetanus immune globulin
    • high risk wound no booster within 10 years
    • no prior immunization or immunization status unknown
• rabies post exposure prophylaxis guidelines
  • wild animals
    • prophylaxis for bites from rabies-endemic species
      • bats anywhere is USA
      • skunks, foxes, raccoons based upon local public health recommendations
    • prophylaxis for bites from wild carnivores (coyotes & bobcats) & groundhogs in rabies-endemic area
    • no treatment necessary for provoked bite from animal where rabies is not endemic in species involved
  • domestic animals
    • no treatment indicated if animal is immunized or healthy & available for 10 days of observation
    • treatment indicated for
      • dogs in most developing countries & in USA along the Mexican border
      • animal rabid or suspected rabid
  • if uncertain, consult local health department
  • specific treatment recommendations
    • previously vaccinated with documented antibody response
      • 2 doses of human diploid cell vaccine (HDCV) or rabies vaccine adsorbed (RVA) 1 mL IM (deltoid) on days 1 & 3
      • do not give rabies immune globulin (RIG)
    • unvaccinated individuals
      • rabies immune globulin (RIG), 20 IU/kg
        • 1/2 infiltrated into the wound the
        • other 1/2 IM (gluteal)
      • 5 doses of HDCV or RVA 1.0 mL IM (deltoid) on days 1, 2, 7, 14, 28
• evaluation of exposure to viral & other pathogens
  • hepatitis B, hepatitis C, HIV1 (human bites)
  • hepatitis B prophylaxis as indicated
    • hepatitis B immune globulin 0.06 mL/kg IM on days 1 & 30
• established wound infections
  • treat aggressively
  • adequate surgical debridement & drainage
  • hospitalize for severe blood loss, sepsis, open fracture, osteomyelitis, severe hand injury, deep tissue injury
  • parenteral antibiotics for hospitalized patients
    • empiric coverage of gram positive, gram negative & anaerobic organisms
  • frequent follow-up
• precautions should be taken if bite is from a known carrier of HIV
• patient education
  • do not run if confronted by threatening dog
  • children should not be left alone with an animal
  • pet ferrets are particularly notorious for bites
  • virtually all animals give warning before biting

More general terms

• animal bite

Additional terms

• cat stratch
• clenched fist injury; closed fist injury; reverse bite injury; fight bite