Human and other mammal bites (mostly dog and cat bites, but also squirrel, gerbil, rabbit, guinea pig, and monkey bites) are common and occasionally cause significant morbidity and disability. The hands, extremities, and face are most frequently affected, although human bites can occasionally involve breasts and genitals.
Bites by large animals sometimes cause significant tissue trauma; about 10 to 20 people in the US, mostly children, die from dog bites each year. However, most bites cause relatively minor wounds.
(See also Rat-Bite Fever.)
Infection
In addition to tissue trauma, infection due to the biting organism’s oral flora is a major concern. Human bites can theoretically transmit viral hepatitis and HIV. However, HIV transmission is unlikely because the concentration of HIV in saliva is much lower than in blood and salivary inhibitors render the virus ineffective.
Rabies is a risk with certain mammal bites. Monkey bites, usually restricted in the US to animal laboratory workers, carry a small risk of herpes simian B virus (Herpesvirus simiae) infection, which causes vesicular skin lesions at the inoculation site and can progress to encephalitis, which is often fatal.
Bites to the hand carry a higher risk of infection than bites to other sites. Specific infections include
A fight bite is the most common human bite wound. It results from a clenched-fist strike to the mouth and is a particular risk for infection. In fight bites, the skin wound moves away from the underlying damaged structures when the hand is opened, trapping bacteria inside. Patients often delay seeking treatment, allowing bacteria to multiply.
Cat bites to the hand also have a high risk of infection because cats’ long, slender teeth often penetrate deep structures, such as joints and tendons, and the small punctures are then sealed off.
Human bites to sites other than the hand have not been proved to carry a greater risk of infection than bites from other mammals.
Diagnosis of Human and Mammal Bites
Evaluation of hand bites while the hand is in the same position as when the bite was inflicted
Assessment for damage to underlying nerve, tendon, bone, and vasculature and for presence of foreign bodies
Human bites sustained in an altercation are often attributed to other or vague causes to avoid involvement of the authorities or to ensure insurance coverage. Domestic violence is often denied.
Pearls & Pitfalls
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Wounds are evaluated for damage to underlying structures (eg, nerves, vasculature, tendons, bone) and for foreign bodies. Evaluation should focus on careful assessment of function and the extent of the bite. Wounds over or near joints should be examined while the injured area is held in the same position as when the bite was inflicted (eg, with fist clenched). Wounds are explored under sterile conditions to assess tendon, bone, and joint involvement and to detect retained foreign bodies. If a retained foreign body is a possibility, imaging (eg, x-ray for radiopaque foreign bodies, such as most teeth) may be done. Ultrasound has also become a valuable tool in detecting subcutaneous foreign bodies. Wounds inflicted by chomping may appear to be minor abrasions but should be examined to rule out deep injury.
Culturing fresh wounds is not valuable for targeting antimicrobial therapy, but infected wounds should be cultured. For patients with human bites, screening for hepatitis or HIV is recommended only if the attacker is known or suspected to be seropositive.
Treatment of Human and Mammal Bites
Meticulous wound care
Selective wound closure
Selective use of prophylactic antibiotics
Hospitalization is indicated if complications from a bite mandate very close monitoring, particularly when patient characteristics predict a high risk of nonadherence with outpatient follow-up. Hospitalization should be considered in the following circumstances:
When a human bite is infected (including clenched-fist injuries)
When a nonhuman bite is moderately or severely infected
When loss of function is evident
When the wound threatens or has damaged deep structures
When a wound is disabling or difficult to care for at home (eg, significant wounds to both hands or both feet, hand wounds that require continuous elevation)
Priorities of treatment include wound cleaning, debridement, closure, and infection prophylaxis, including for tetanus (see table Tetanus Prophylaxis in Routine Wound Management).
Wound care
Bite wounds should first be cleaned with a mild antibacterial soap and water (tap water is sufficient), then pressure irrigated with copious volumes of saline solution using a syringe and IV catheter. A local anesthetic should be used as needed. Dead and devitalized tissue should be debrided, taking particular care in wounds involving the face or the hand.
Wound closure is done only for select wounds (ie, that have minimal damage and can be cleansed effectively). Many wounds should initially be left open, including the following:
Puncture wounds
Wounds to the hands, feet, perineum, or genitals
Wounds more than several hours old
Wounds that are heavily contaminated
Wounds that are markedly edematous
Wounds that show signs of inflammation
Wounds that involve deeper structures (eg, tendon, cartilage, bone)
Wounds due to human bites
Wounds sustained in a contaminated environment (eg, marine, field, sewers)
In addition, in immunocompromised patients, wound healing may be better with delayed closure. Other wounds (ie, fresh, cutaneous lacerations) can usually be closed after appropriate wound hygiene. Results with delayed primary closure are comparable to those with primary closure, so little is lost by leaving the wound open initially if there is any question.
Hand bites should be wrapped in sterile gauze, splinted in position of function (slight wrist extension, metacarpophalangeal and both interphalangeal joints in flexion). If wounds are moderate or severe, the hand should be continuously elevated (eg, hanging from an IV pole).
Facial bites may require reconstructive surgery given the cosmetic sensitivity of the area and the potential for scarring. Primary closure of dog bites of the face in children has shown good results, but consultation with a plastic surgeon may be indicated.
Infected wounds may require debridement, suture removal, soaking, splinting, elevation, and IV antibiotics, depending on the specific infection and clinical scenario. Joint infections and osteomyelitis require prolonged IV antibiotic therapy and orthopedic consultation.
Antimicrobials
Thorough wound cleansing is the most effective and essential way to prevent infection and often suffices. There is no consensus on indications for prophylactic antibiotics. Studies have not confirmed a definite benefit, and widespread use of prophylactic antibiotics has the potential to select resistant organisms. Drugs do not prevent infection in heavily contaminated or inadequately cleaned wounds. However, many practitioners prescribe prophylactic antibiotics for bites to the hand and some other bites (eg, cat bites, monkey bites).
Infections are treated with antimicrobials initially chosen based on animal species (see table Antimicrobials for Bite Wounds). Culture results, when available, guide subsequent therapy.
Patients with human bites that cause bleeding or exposure to the biter's blood should receive postexposure prophylaxis for viral hepatitis and HIV as indicated by patient and attacker serostatus. If status is unknown, prophylaxis is not indicated.
Key Points
Infectious risk is high for hand wounds, particularly clenched-fist injuries.
Evaluate hand wounds with the hand in the position it was when the wound was inflicted.
Evaluate wounds for damage to nerve, tendon, bone, and vasculature and for the presence of foreign bodies.
Close only wounds that have minimal damage and can be cleansed effectively.
Decrease risk of infection by thorough mechanical cleaning, debridement, and sometimes antimicrobial prophylaxis.
