Animal Bites in Emergency Medicine 

Because many animal bites are never reported, determining the exact incidence of bite wounds in the United States, let alone the world, is difficult. An estimated 74.8 million dogs lived in the United States in 2007; these account for an estimated 5 million dog bites per year, over which 800,000 require medical attention^[1] . Substantially more dog bites occur than cat bites. These two species account for the majority of (non-human) mammalian bite wounds encountered in the emergency department (ED).

Dog bites typically cause a crushing-type wound because of their rounded teeth and strong jaws. An adult dog can exert 200 pounds per square inch (psi) of pressure, with some large dogs able to exert 450 psi.^[2] Such extreme pressure may damage deeper structures such as bones, vessels, tendons, muscle, and nerves.

A bite from a pit bull is shown below.

The sharp pointed teeth of cats usually cause puncture wounds and lacerations that may inoculate bacteria into deep tissues. Infections caused by cat bites generally develop faster than those of dogs.^{[3, 4]}

Limited literature is available on other mammalian bites. Monkey bites have a notorious reputation based largely on anecdotal reports. Several cases of unprovoked attacks on young children and infants by domesticated ferrets have been documented. The bites of foxes, raccoons, skunks, bats, dogs, and cats have been clearly linked to rabies exposure. Bites from large herbivores generally have a significant crush element because of the force involved.

Bites of the hand generally have a high risk for infection because of the relatively poor blood supply of many structures in the hand and anatomic considerations that make adequate cleansing of the wound difficult. In general, the better the vascular supply and the easier the wound is to clean (ie, laceration vs puncture), the lower the risk of infection.

A major concern in all bite wounds is subsequent infection. Infections can be caused by nearly any group of pathogens (bacteria, viruses, rickettsia, spirochetes, fungi). At least 64 species of bacteria are found in the canine mouth, causing nearly all infections to be mixed.^{[5, 6, 7]} Common bacteria involved in bite wound infections include the following:

• Dog bites

  • Staphylococcus species
  • Streptococcus species
  • Eikenella species
  • Pasteurella species
  • Proteus species
  • Klebsiella species
  • Haemophilus species
  • Enterobacter species
  • DF-2 or Capnocytophaga canimorsus
  • Bacteroides species
  • Moraxella species
  • Corynebacterium species
  • Neisseria species
  • Fusobacterium species
  • Prevotella species
  • Porphyromonas species
• Cat bites

  • Pasteurella species
  • Actinomyces species
  • Propionibacterium species
  • Bacteroides species
  • Fusobacterium species
  • Clostridium species
  • Wolinella species
  • Peptostreptococcus species
  • Staphylococcus species
  • Streptococcus species
• Herbivore bites

  • Actinobacillus lignieresii
  • Actinobacillus suis
  • Pasteurella multocida
  • Pasteurella caballi
  • Staphylococcus hyicus subsp hyicus
• Swine bites

  • Pasteurella aerogenes
  • Pasteurella multocida
  • Bacteroides species
  • Proteus species
  • Actinobacillus suis
  • Streptococcus species
  • Flavobacterium species
  • Mycoplasma species
• Rodent bites - Rat-bite fever

  • Streptobacillus moniliformis
  • Spirillum minus
• Primates

  • Bacteroides species
  • Fusobacterium species
  • Eikenella corrodens
  • Streptococcus species
  • Enterococcus species
  • Staphylococcus species
  • Enterobacteriaceae
  • Simian herpes virus
• Large reptiles (crocodiles, alligators)

  • Aeromonas hydrophila
  • Pseudomonas pseudomallei
  • Pseudomonas aeruginosa
  • Proteus species
  • Enterococcus species
  • Clostridium species

Frequency

United States

Of an estimated 3-6 million animal bites per year in the United States,^[8] approximately 80-90% are from dogs, 5-15% are from cats, and 2-5% are from rodents, with the balance from other small animals (eg, rabbits, ferrets), farm animals, monkeys, reptiles, and others. Some estimate that 1% of emergency visits are for dog bite wounds. Approximately 1% of dog bite wounds and 6% of cat bite wounds require hospitalization.^{[1, 9]}

International

The lack of standard reporting in many countries makes accurate estimates of mammalian bite incidence difficult to determine. Depending on locale, the range of animals inflicting bites is wide and includes large cats (tigers, lions, leopards), wild dogs, hyenas, wolves (Eurasia), crocodiles, and other reptiles. As in the United States, most bites, however, are from domestic dogs. In developing countries, mammalian bites (especially bites by dogs, cats, foxes, skunks, and raccoons) carry a high risk of rabies infection.

Mortality/Morbidity

Dog attacks kill approximately 20-35 people annually in the United States.^{[8, 10, 11]} Many of these fatalities, unfortunately, are young children. While local infection and cellulitis are the leading causes of morbidity, sepsis is a potential complication of bite wounds, particularly C canimorsus (DF-2) sepsis in immunocompromised individuals. Pasteurella multocida infection (the most common pathogen contracted from cat bites) also may be complicated by sepsis. Meningitis, osteomyelitis, tenosynovitis, abscesses, pneumonia, endocarditis, and septic arthritis are additional concerns in bite wounds. When rabies occurs, it is almost uniformly fatal (Rabies).

Sex

Women are more frequently bitten by cats, whereas men are more often bitten by dogs (despite being man's best friend).^[12]

Age

Peak incidence of animal bites occurs among children aged 5-9 years.^{[9, 8, 10]}