Animal Bites

Etiology

Domesticated cats and dogs inflict practically all of the bites encountered in the emergency department in the United States. The most common complication is a local wound infection. Infections resulting from bites of all animal species are polymicrobial with aerobic and anaerobic bacteria; dogs and cats have an oral flora of Pasteurella, Staph, and Strep most commonly. In cat bites and scratches, Bartonella infections are an additional concern. Dog bites in immunocompromised individuals, especially asplenic patients, raise concern for Capnocytophaga sepsis.[4]      

Epidemiology

Dog bites predominate (60%-90%), followed by cat bites (5%-20%). Children are more commonly bitten on the head, face, and neck due to their proportionately larger heads and shorter stature, while adult bites are more common on the hands and arms. Dog bites happen more in men and children. The patient usually knows the dogs, and the bites are less commonly provoked. Cat bites are more common in women and adults, and the bites more often result from provocation. In less traumatic bites, especially cat bites due to the puncturing nature of cat teeth, the patient commonly only presents after the infection has become apparent, and management has become more complicated.[1][5][1]

Pathophysiology

The initial injury is the result of the physical trauma of teeth puncturing or tearing soft tissue, and in the case of some dog bites, blunt force breaking bones. Dog bites are more commonly macerated due to the ripping and tearing forces involved. Cat bites are narrow and deep as the animal rarely pulls or shakes its head, simply biting and holding. Because the cat bite wound is deep and narrow, it is much more likely to seal itself relatively quickly, providing an anaerobic environment for the inoculated bacteria and initially appearing less consequential and prolonging the time to seek medical care. 

History and Physical

Focused history and physical examination should determine the circumstances surrounding the bite, location of the bite, type of animal, time of occurrence, and whether the patient has been febrile, has local erythema, swelling, warmth, or has purulent drainage. If the patient is stable, the wound should be thoroughly explored after local or regional anesthesia to determine the potential for damage to underlying structures and foreign body inoculation. Local and distal neurovascular status should be assessed after anesthesia, as well as pain and apprehension, which may affect patient compliance with the exam. Pertinent history includes any immunosuppression, be it iatrogenic (transplant, rheumatic disease treatment) or a disease process (eg, diabetes, HIV/AIDS, sickle cell disease)

Evaluation

As with all traumas, the initial evaluation is to ensure airway, breathing, and circulation is intact. Active venous bleeding should be controlled with direct pressure, while arterial bleeding typically necessitates consult services. The examiner should explore the wounds of foreign bodies, such as broken teeth, claws, dirt, and plant material. When analyzing the wound, underlying structures also require assessment for potential damage. During exploration, the patient should range the underlying structures through a full range of motion to ensure no injuries to those underlying structures.[2]

Treatment / Management

All wounds require extensive irrigation, and the patient’s tetanus status is updated if necessary. Provide appropriate pain management before exploration, irrigation, or debridement of the wounds. If necessary, the patient’s tetanus, diphtheria, and pertussis (TDaP) status should be updated. For uncomplicated dog bites, the patient should be educated on the risk/benefit of closure versus healing by secondary intention and the decision made with the provider. If the patient presents delayed from the initial bite, the risks of closing the wound almost certainly outweigh the cosmetic benefits of closure. If the wound is closed, the patient should be discharged with a week’s course of amoxicillin-clavulanate.

Complicated dog bites should be stabilized and referred for the appropriate consultation service. Cat bites deeper than superficial, so thorough irrigation under local anesthesia is needed, and the wound is left open. The patient should be discharged with a week of amoxicillin-clavulanate and given strict wound care precautions. All bites to the hands or feet, bites in immunocompromised individuals, bites that already show signs of infection, and bites with a puncture characteristic require treatment with amoxicillin-clavulanate. Second-line therapy for patients with penicillin allergies is doxycycline or trimethoprim-sulfamethoxazole (TMP-SMX) plus metronidazole or clindamycin. The appropriate consult service should see patients with extensive local infection; patients with evidence of disseminated infection should be treated with broad-spectrum IV antibiotics and admitted for further care.[6][7][8](B3)

Differential Diagnosis

The differential diagnoses for animal bites include the following:

• Cellulitis
• Cervical spine fracture evaluation
• Emergency treatment of rabies
• Hand infections
• Human bites
• Neck trauma
• Osteomyelitis in emergency medicine
• Tetanus

Prognosis

The prognosis for most animal bites is excellent. However, it is essential to know that, on average, about 30 to 50 people die from dog bites each year.

Complications

The complications that can manifest with animal bites are as follows:

• Cellulitis
• Tenosynovitis
• Endocarditis
• Osteomyelitis
• Abscess
• Meningitis
• Tendon rupture
• Nerve injury
• Post-traumatic stress disorder
• Rabies