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Human and Mammal Bites

by Robert A. Barish, MD, MBA, Thomas Arnold, MD

(See also Rat-Bite Fever.)

Human and other mammal (mostly dog and cat, 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, mostly children, die from dog bites each year. However, most bites cause relatively minor wounds.

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 (see Rabies). 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 (see also Infected Bite Wounds of the Hand) carry a higher risk of infection than bites to other sites. Specific infections include

This higher risk is a particular concern after a clenched-fist strike to the mouth (a fight bite), the most common human bite wound. 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. Human bites to sites other than the hand have not been proved to carry a greater risk of infection than bites from other mammals. 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.

Diagnosis

  • 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

  • For any wound near the metacarpophalangeal joint, consider a human bite, particularly if the history is vague.

Wounds are evaluated for damage to underlying structures (eg, nerves, vasculature, tendons, bone) and for foreign bodies (see Lacerations : Evaluation of Lacerations). 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. 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

  • Meticulous wound care

  • Selective wound closure

  • Selective use of prophylactic antibiotics

Hospitalization is indicated if complications 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.

Wound care

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 a 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 (see Acute Viral Hepatitis : Prevention) and HIV (see Postexposure prophylaxis (PEP)) as indicated by patient and attacker serostatus. If status is unknown, prophylaxis is not indicated.

Antimicrobials for Bite Wounds

Drug

Dose

Comments

Human and dog bites

Amoxicillin/clavulanate

500–875 mg po bid

For outpatients

Prophylaxis: Give for 3 days

Treatment: Give for 5–7 days

Ampicillin/sulbactam

1.5–3.0 g IV q 6 h

For inpatients

Effective against α-hemolytic streptococci, Staphylococcus aureus, and Eikenella corrodens

Trimethoprim/sulfamethoxazole

plus

160/800 mg IV q 12 h

For penicillin-allergic patients (use weight-appropriate doses for children)

Clindamycin

150–300 mg IV q 6 h

Doxycycline

100 mg po or IV q 12 h

Alternative for dog bites in penicillin-allergic patients, except children < 8 yr and pregnant women

Clindamycin

plus

150–300 mg po or IV q 6 h

Alternative for dog bites in adults

A fluoroquinolone (eg, ciprofloxacin)

500 mg po q 12 h (ciprofloxacin)

Cat bites*

A fluoroquinolone (eg, ciprofloxacin)

500 mg po bid for 5–7 days

For prophylaxis and treatment in adults

Effective against P. multocida

Clarithromycin

500 mg po bid for 7–10 days

Alternative for children

Clindamycin

150–300 mg po qid for 7–10 days

Alternative for children

Monkey bites

Acyclovir

800 mg IV 5 times/day for 14 days

For prophylaxis

*Squirrel, gerbil, rabbit, and guinea pig bites rarely become infected, but when they do, they can be treated with the same drugs used to treat infected cat bites.

Bartonella henselae—see Cat-Scratch Disease—is also transmitted by cat bites.

For treatment of infected monkey bites, use antibacterial drugs similar to those used for infected human and dog bites.

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.

Resources In This Article

Drugs Mentioned In This Article

  • Drug Name
    Select Trade
  • ZOVIRAX
  • PERIOSTAT, VIBRAMYCIN
  • AMOXIL
  • CILOXAN, CIPRO
  • CLEOCIN
  • No US brand name
  • BIAXIN

* This is a professional Version *