Animal Bites
Toni Gross
INTRODUCTION
Humans have contact with animals in a variety of occupational and recreational settings, and over half of households in the United States have at least one pet. Animal and human bite wounds are frequent in the pediatric population and are treated in primary care offices and emergency departments. As a result, all pediatric practitioners should be familiar with evaluation and management of the most common animal bite wounds. The complex microbiology of animal bite wounds makes management a challenging clinical problem, and therapy is often empiric.
DIFFERENTIAL DIAGNOSIS LIST
Lacerations, fractures, crush injuries, and tendon and nerve injuries
Local bacterial wound infection—mouth flora vary by species (Table 14-1)
Rabies—many animals, especially dogs, cats, bats, foxes, raccoons, and skunks
Tularemia—many animals, especially rabbits, cats, squirrels, pigs, sheep, coyotes, and ticks
Rat-bite fever
Cat-scratch disease (CSD)
Crotalinae envenomation
DIFFERENTIAL DIAGNOSIS DISCUSSION
Dog and Cat Bites
Dog and cat bites make up the majority of bite wounds, accounting for 85% and 10%, respectively. Because of their inquisitive nature and decreased protective mechanisms, children are bitten by dogs and cats three times more frequently than adults, with most bites occurring in the 5- to 9-year-old age group. Their size relative to an animal causes children to sustain more facial bites, resulting in greater severity of laceration, infection, disability, and death, especially when large dogs are involved. Cat bite wounds are typically puncture wounds that involve the hand or extremity. The sharp and slender nature of cat’s teeth can penetrate bones, which may lead to greater morbidity from complicated wounds.
TABLE 14-1 Organisms Commonly Associated with Bite Wounds | ||||||||||||||||||||||||||||||||||||||||||
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Dog bites have an infection rate of approximately 5% to 15%, the lowest of all mammalian bites. Cat bites become infected more frequently (˜50%). Wound characteristics and initial wound care determine the risk of infection. Puncture wounds, wounds on the hands or feet, those involving joints, tendons, or other deep structures and those in hosts with comorbid illness or immunosuppression are at higher risk for infection. Wounds treated more than 12 hours after the injury and those not properly irrigated and debrided are more likely to become infected. The microbiology of infected dog and cat bite wounds has been well studied (see Table 14-1). Most bite wound infections are polymicrobial and include anaerobic organisms.
Human Bites
Following dog and cat bites, human bites are the next most common type of mammalian bite injuries. Human bites are most commonly seen in teenage or young adult males and are often related to aggressive behavior, sports, and sexual activity. Wound infections occur in about 15% to 50% of human bites.
Delays in care, which are common as a result of the circumstances of injury, have a direct effect on infection rates and prognosis. Simple bites that occur from occlusion of the teeth on skin, such as bites occurring in daycare, rarely become infected. Human bite infections are polymicrobial with a mixture of anaerobes and aerobes (see Table 14-1). Eikenella corrodens deserves special mention, as it is present in 25% of isolates from clenched fist injuries. It has also exhibited synergistic growth with other aerobic organisms.
HINT: When a bite occurs as the result of a direct blow of the victim’s hand into the biter’s mouth, there is typically a puncture wound overlying one of the metacarpal-phalangeal joints on the dorsum of the hand (clenched-fist syndrome). Penetration of the joint capsule may occur with tendon, nerve, or bone damage. These wounds may appear mild at first, but are deceiving and can result in extensive infection that requires surgical exploration, debridement, and intravenous antibiotics.Other significant infectious diseases like Herpes virus, syphilis, tuberculosis, actinomycosis, tetanus, and hepatitis B and C have also been documented as occurring through human bites. Although there have been no definitive cases of HIV transmission from this route, detection of HIV in saliva makes this an unlikely but possible way to acquire HIV infection.
Complications
Local Wound Infection
Characteristics of infected bite wounds include erythema, warmth, fluctuance, purulent drainage, and/or tenderness at the site, and can include surrounding edema and regional adenitis. Local wound infections can also be accompanied by mild systemic symptoms, such as fever, chills, and malaise, and may be associated with serum leukocytosis.
Various clinical syndromes may help differentiate the type of organism that predominates in a bite-wound infection. Infection caused by Pasteurella species may evolve rapidly with intense cellulitis and lymphangitis within 24 hours. Cellulitis caused by Staphylococcus or Streptococcus species usually evolves more slowly and may be associated with abscess formation. More serious infections, such as osteomyelitis or septic arthritis, may present with increased pain and decreased movement of the affected part. Deep infections may occur after direct inoculation into deeper tissues or by localized extension of cellulitis. Immunocompromised hosts can present with local or systemic infections and are at higher risk for invasive disease, specifically with Capnocytophaga canimorsus, which is associated with a 25% mortality rate.
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