In the United States, as many as 1% of all pediatric visits to emergency departments during the summer months are for the treatment of human or animal bite wounds, and an estimated 1% to 2% of all bite wounds require hospitalization.¹ There are an estimated 4 to 5 million bite occurrences annually. Dog bites constitute the majority of these, at about 80%, with cat bites accounting for 5% to 20%, human bites 2% to 3%, rodent bites 2% to 4%, and other animals comprise the rest. Despite the fewer number of cat bites, they are disproportionately responsible for infections, with the rate of infection after a cat bite reported as high as 50% and the rates of infection after dog or human bites reported at 10% to 15%.² No matter what type of bite, there is a risk of morbidity and sometimes mortality. Although infection is by far the most common complication, physical trauma certainly plays a role. An average of 10 to 15 deaths occur following dog bites each year in the United States, mostly due to major bleeding and crush injuries following dog bites to the head and neck region.

In general, bite wounds that most often require medical attention are those to the extremities, especially the dominant hand. However, dog bites to the head and neck region are more common in children, and occur in 60% to 70% of attacks in children below the age of 5 years and in 50% of those 5 to 10 years old. This is likely because of the height of a child and the proximity of a child’s head to the mouth of an animal and also because of a child’s generally uninhibited behavior. Males are also more likely than females to sustain a dog bite and bites are usually unprovoked, although for children less than 5 years old, there is no statistical difference between boys and girls getting bitten by dogs.³ In contrast, females and adults are more commonly bitten by cats and 89% of these bites are provoked.⁴

The time of presentation of the patient to medical care can be telling. Patients who present for medical care within 8 to 12 hours after injury are usually concerned with crush injury, care of disfiguring wounds, or the need for rabies or tetanus therapy. These wounds are frequently contaminated with multiple strains of aerobic and anaerobic bacteria. An estimated 2% to 30% of “treated” wounds will still become infected and may require hospitalization. Patients presenting longer than 12 hours after injury usually have established infection.

In this chapter, both mechanical injury and infection as a result of dog, cat, and human bites are discussed. Included are topics that warrant special consideration, such as clenched-fist injuries, bites to the face, bites to the hand, immunocompromised patients, and rabies. Although other mammalian bites are not discussed, it is of note that monkey and simian bites are becoming more common, and other types that may be seen include those by horses, pigs, aquatic animals, ferrets, and bird pecking and bites. Rodent bites carry a low risk of secondary infection. Rat-bite fever is a rare infection manifested by fever, chills, headache, malaise, and rash 1 to 3 weeks after the bite. Rabbit bites can cause tularemia, most frequently of the ulceroglandular type.

Bite wounds result in morbidity and mortality through both physical trauma and infection. Dog bites can cause a spectrum of injuries from lacerations to avulsions and crush injuries. Dog’s teeth are not very sharp but can exert a pressure of 200 to 450 psi.⁵ This pressure is strong enough to perforate sheet metal and result in a crush injury with much devitalized tissue. Such bites can result in physical trauma as well as infection-prone devitalized tissue. The scalp, face, and neck are sites of injury in more than 80% of dog bites in the United States each year. The thin and immature calvaria of a young child has little resistance to the pressure that can be exerted by a dog bite, and a small, apparently minor cranial puncture can be associated with a breach in dural integrity, which carries with it a high risk of intracranial infection.

Bites from dogs, cats, and humans carry risks for different types of injuries. Dog bites can result in vascular injuries. Injuries to the brachial artery are regularly encountered with dog bites and have an attendant risk of significant blood loss. Cat bites have the highest infection rates, likely related to their bites often being puncture wounds that inoculate the bacteria deeply and their mouth flora having a high prevalence of Pasturella multocida. Human bites commonly involve injury to the hand after fist-to-mouth contact, often seen in teens. In younger children, a bite to the face or trunk is more common. Child abuse needs to be considered when human bites are involved. Bite marks with an intercanine distance of >3 cm are considered to be inflicted by an adult and are more concerning for abuse.^6,7

Infection generally results from mouth organisms of the biting mammal. The type of infection depends on the nature of the injury and the proximity/involvement of bones or joints. Infections can be manifested as cellulitis, septic arthritis, osteomyelitis, tenosynovitis, or local abscesses in any potential anatomic space. Regional lymphadenopathy or lymphangitis may develop. Penetrating skull wounds may result in meningitis or a brain abscess. Septicemia occurs primarily in immunocompromised patients, particularly those who are asplenic and therefore more susceptible to infection with encapsulated organisms. Endocarditis is likewise a rare complication. Important prognostic factors for the development of infection include the extent of tissue damage, the depth of the wound and which compartments are entered, the pathogenicity of the inoculated oral bacteria, and the immunocompetence of the host.

The infectious organisms vary with the source of the bite, and the bacteria recovered from infected bite wounds are most often reflective of the oral flora of the biting animal. However, bacteria may also originate from the victim’s own skin or the physical environment at the time of injury. Bites should, therefore be considered polymicrobial infections, including both aerobes and anaerobes. The organism most commonly found in both dog and cat bites is Pasteurella, with P. canis being the most common from dogs and P. multocida the most common from cats. Other species commonly isolated from these bites include streptococci, staphylococci, Moraxella species, Neisseria species, enterococcus, and Corynebacterium species. Common anaerobic isolates include Fusobacterium, Bacteroides, Porphyromonas, Prevotella, Propionibacterium, and Peptostreptococcus. Capnocytophaga species (formerly the DF-2 bacillus) have been implicated in endocarditis, septicemia, and other more severe infections, primarily in immunocompromised hosts.^8,9 Of note, cats are also the main reservoir of Bartonella henselae, the causative agent of cat scratch disease. Cat scratch disease most commonly presents as regional tender lymphadenopathy and less commonly can cause a myriad of other systems involvement, including but not limited to liver, spleen, ocular, central nervous system, fever of unknown origin, and endocarditis.¹⁰

In human bites, the most common aerobic organisms isolated are streptococci, Staphylococcus aureus and Eikenella species; and the most common anaerobic organisms are Bacteroides, Pepto streptococcus species, and Fusobacterium species. More serious morbidity of human bites correlates with S. aureus and Eikenella corrodens infection. Human bite injuries also represent a potential means of transmitting human immunodeficiency virus (HIV), hepatitis B (HBV), hepatitis C (HCV), and herpes simplex infections (HSV).¹¹ HIV transmission by this route has been reported rarely.^12,13 Transmission could theoretically occur either through biting or receiving a bite from an HIV-infected person. Biting an HIV-infected person, with a break in the skin, exposes the oral mucous membranes to infected blood; being bitten by an HIV-infected person exposes nonintact skin to saliva. Saliva that is contaminated with infected blood poses a more substantial exposure risk. Saliva that is not contaminated with blood contains HIV in much lower titer and constitutes a negligible exposure risk.¹⁴ There are also case reports documenting transmission of HCV through human bites, although numbers defining absolute risk are not available.

Fatal attacks represent a small proportion of dog bite injuries to humans, but death can occur from massive trauma after mauling.¹⁵ Sepsis with Capnocytophaga canimorsus or Eubacterium plautii has been described in immunocompromised hosts.¹⁶ Endocarditis from Pasteurella species other than Multocida, C. canimorsus, and S. aureus has occurred after minor bites.^17,18 Patients with crush injuries to the limbs are at risk for compartment syndrome. Joint and bone infections; meningitis or brain abscess; facial, neck, or limb deformities; or limb loss can occur after bites.

Certain features of a routine complete history and physical examination warrant particular attention. The focus may vary by type of bite and time of presentation after the bite (Tables 175-1 and 175-2).

Further evaluation focuses on determining the extent of injury or the extent or type of complicating infection (or both). Plain radiographs are helpful if a fracture, foreign body (teeth or teeth fragments), or bone penetration is suspected. Radiographic evaluation of dog bite injuries to the scalp, face, and neck in children helps identify occult cranial puncture wounds, which can result in the introduction of microbes into the intracranial space. Skull films in both the anteroposterior and lateral projections need to be obtained and scrutinized carefully for evidence of fracture. For deep puncture wounds to the extremities, multiple views may reveal small cortical defects. Such findings can serve as baseline information if concerns of osteomyelitis arise in the future.

Because of the polymicrobial nature of bite wounds, aerobic cultures and Gram stain are paramount in the evaluation of wounds suspected of infection. Anaerobic cultures should be performed if there is abscess formation, sepsis, serious cellulitis, devitalized tissue, or a foul odor of any exudate. Culture and Gram stain of fresh uninfected wounds are not recommended. Blood cultures should be considered if fever or other systemic signs of sepsis are present, especially in immunocompromised children.

INITIAL STABILIZATION

Patients presenting for care secondary to a bite wound should first be assessed for adequate airway, breathing, and circulation (ABCs), especially if the wound involves the head and neck. After stabilization of the ABCs, the secondary survey should be attentive to large areas of devitalized tissue, possible neurovascular injuries, or penetrating injuries to any bone or organ. Once life-threatening or catastrophic injuries have been stabilized or excluded from consideration, attention can be directed toward local wound assessment and care.

Initial management of bite wounds involves irrigation, debridement, wound closure if indicated, and protection from infection. These management steps are usually carried out before hospitalization but are discussed here briefly.

Bite wounds should be meticulously cleansed. High-pressure irrigation is accomplished with large volumes (at least 200 mL) of sterile normal saline delivered via a 20- to 60-mL syringe and 18-gauge catheter.¹⁹ Irrigation of puncture wounds is controversial because irrigation of this type of wound may merely infiltrate the surrounding tissue.²⁰ Surgical debridement is necessary to remove any devitalized or necrotic tissue as well as any debris or foreign bodies not removed with irrigation. Operative exploration and debridement may be necessary if there is extensive tissue damage, any concern for muscle, nerve, or vascular injury, involvement of the metacarpophalangeal (MCP) joint from a clenched-fist injury, or cranial injury from the bite of a large animal.¹¹