Human and animal bites

In the United States, animal and insect bites cause about 100 deaths per year, and there are >90,000 poison control center calls, with many cases going unreported. Tetanus prophylaxis is required for all victims of insect and animal bites.

The most common bites are from humans and mammals (mostly dog and cat bites, but also squirrel, gerbil, guinea pig and monkey bites), which can cause serious functional impairment. The most common sites of bites are the hands, limbs and face, sometimes the chest and external genitalia are affected.

In addition to the actual tissue injury, infection by the mouth microflora of the biter is very dangerous. Human bites can theoretically transmit viral hepatitis and human immunodeficiency virus (HIV). Bites to the hand are associated with a higher risk of infection, especially cellulitis, tenosynovitis, septic arthritis, and osteomyelitis, compared to other parts of the body. This risk is especially high in human bites resulting from a direct blow to the mouth with a clenched fist (a "fight bite"). Human bites to other parts of the body do not carry as high a risk of infection as bites from other mammals.

Rabies is discussed in the relevant article.

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Diagnosis of human and animal bites

Bite wounds are examined to rule out injury to adjacent structures (eg, nerves, vessels, tendons, bones) and to detect foreign bodies. Wound examination should focus on carefully determining the extent and extent of the bite injury. Wounds over or near joints should be examined at the extremes of joint motion (eg, with a clenched fist) and under sterile conditions to detect injury to tendons, bones, joint structures, and foreign bodies. Cultures of fresh wounds are of no value in selecting antibiotic therapy, but cultures from infected wounds should be taken. Screening of a bite victim for viral hepatitis and HIV is appropriate only if the assailant is known to be seropositive or there is reason to suspect the infection.

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Treatment of human and animal bites

Hospitalization is indicated when infection or loss of function is evident on admission, when wounds are deep or there is a risk of damage to adjacent structures, and when the likelihood of spontaneous wound closure is questionable. Treatment priorities include wound cleansing, debridement, closure, and infection prevention.

Wound care

First, the wound should be cleaned with mild antibacterial soap and water (irrigation with nonsterile water is acceptable), then irrigated with copious amounts of 0.9% saline solution using a syringe and intravenous catheter. A diluted povidone-iodine solution (10:1 with 0.9% saline) may also be used, but irrigating with 0.9% saline solution cleans the wound better. A local anesthetic may be used if necessary. Dead and nonviable tissue is removed.

There are many different ways to close a wound. Many wounds are best left open at first, including the following:

• punctate wounds;
• wounds of the hand, foot, perineum or genitals;
• wounds inflicted more than a few hours ago;
• heavily contaminated, clearly swollen, with signs of inflammation or with damage to nearby structures (eg, tendon, cartilage, bone);
• human bite wounds;
• wounds that have been in contact with a polluting environment (e.g. sea water, field, sewage system).

In addition, wounds in immunocompromised patients are better treated with delayed closure. Other wounds (e.g., fresh, lacerated) can usually be closed after appropriate treatment. If in doubt, it should be borne in mind that the results of delayed primary closure are not significantly different from those of primary closure, so leaving the wound open does not mean losing anything.

In case of hand bites, a sterile gauze bandage should be applied, immobilized in a functional position (slight wrist extension, flexion at the metacarpophalangeal and interphalangeal joints) and kept in an elevated position at all times. In case of bites in cosmetically significant and scar-prone areas of the face, reconstructive surgery may be required.

Prevention of infection

In most cases, careful wound hygiene is sufficient to prevent infection. There is no consensus on the indications for antibiotic therapy. Medications will not prevent infection in heavily contaminated or improperly treated wounds, but many physicians prescribe antibiotics prophylactically for hand bites and some other localizations. For dog and human bites, amoxicillin + [clavulanic acid] 500-875 mg orally 2 times a day for 3 days (prophylaxis) or 5-7 days (treatment) for outpatients is preferred for prophylaxis and treatment. For inpatients, ampicillin + [sulbactam] 1.5-3 g every 6 hours is considered a reasonable empirical choice; It covers the a-hemolytic streptococci, Staphylococcus aureus Eikenella corrodens, the organisms most commonly isolated from human bites, and various species of Pasteurella (P. canis P. multocida) and Capnocytophaga canimorsus, found in dog bites. In cat bites, fluoroquinolones (eg, ciprofloxacin 500 mg orally for 5–7 days) are recommended for prophylaxis and treatment because of the presence of P. multocida. (Bartonella henselae is also transmitted by cat bites.) Alternative medications for patients with penicillin allergy include clarithromycin 500 mg orally for 7–10 days or clindamycin 150–300 mg orally for 7–10 days. Squirrel, gerbil, rabbit and guinea pig bites are less likely to cause infection but are treated in the same way as cat bites.

For victims of human bites, indications for prophylaxis against viral hepatitis and HIV depend on the serological status of the victim and the attacker.

Infected wounds

In case of infection, antibiotics are initially prescribed empirically, depending on the characteristics of the bite, see above. Further treatment is based on the results of wound culture. Wound debridement, suture removal, wetting and intravenous antibiotics depend on the specific infection and clinical picture. Joint infection and osteomyelitis may require long-term intravenous antibiotics and orthopedic consultation.

Monkey bites (in the United States, mostly among vivarium workers) are associated with a small risk of herpesvirus simiae infection, which causes vesicular skin lesions on the side of the bite. However, encephalitis, often fatal, can occur with these bites. Treatment is with intravenous acyclovir.