Human and Animal Bites:

September 1, 2005
Ralph Riviello, MD
Ralph Riviello, MD

,
Kenneth G. Lavelle, MD
Kenneth G. Lavelle, MD

Each year almost 5 million Americans sustain an animal or human bite. Dog bites alone represent 0.4% to 1% of all emergency department (ED) visits and can range from trivial to life-threatening.

Each year almost 5 million Americans sustain an animal or human bite.1-3 Dog bites alone represent 0.4% to 1% of all emergency department (ED) visits and can range from trivial to life-threatening.2,4-7

Victims of bite wounds are often emotionally distraught, whether from the severity of the injury, concern about the appearance of the wound, or the fact that their pet has just hurt them. Post-traumatic stress disorder is not uncommon among children who are bitten by dogs.8

You can do much to calm and reassure bite victims. Here we provide strategies that can minimize the risk of infection and disease and help ensure satisfactory wound healing.

ANIMAL BITES

Dog. There are 53 to 68 million domestic dogs in the United States.1,9,10 Dogs are responsible for 80% of all animal bites. Each year about 585,000 dog bites require medical attention, and 340,000 are managed in an ED.1,9,11 Most persons are treated and released; however, 2% to 4% require hospitalization, and approximately 20 deaths occur per year.1,7,9

Most fatal attacks involve children and are usually caused by an unrestrained dog on the dog owner's property.12 The typical dog-bite victim is a child, aged 5 to 9 years, who knows the biting animal and who has an extremity wound. Common offending breeds include rottweilers, chows, pit bulls, and German shepherds.3,9,12 In 80% of cases, the dog is known to the victim or family; in 70% of cases, the bite occurs in a familiar location.4,13 About 4% to 25% of dog bites result in infection, usually within 24 hours of the injury.4,6,10,11,14

Cat. More than 57 million cats are kept as pets in the United States; one is present in every third household.5 Cat bites represent between 3% and 15% of all animal bites. Most victims of cat bites are older women, and the bite usually occurs on the hand.4,5

Because cats have sharp, pointed teeth, their bite is likely to cause puncture wounds. From 30% to 80% of cat bites become infected, typically within 12 hours of the injury.4,5,11,14

Other animals. Although many other animals, such as primates, pigs, horses, and camels, can bite humans, only rodents represent a significant percentage of bite wounds (up to 7%). Ferrets, which have become popular pets, can attack humans, particularly small children.

Bites from animals other than dogs and cats often occur during job-related contact. In general, treat bites from these animals as you would treat dog and cat bites.3

Bites or scratches from rhesus and other macaque monkeys deserve special attention; these injuries usually occur in zoo or research laboratory workers. Monkeys can transmit herpesvirus simiae (B virus), which can cause fatal encephalitis. Acyclo-vir must be started immediately after exposure.15,16

HUMAN BITES

Bites from humans occur during aggression, sports, and sexual activity.4 There are 2 distinct types: occlusion and clenched fist. An occlusion injury occurs when the perpetrator's teeth enter the victim's skin. The bite injury is on the victim. The wound poses a relatively low risk of infection.

A clenched fist injury (fight bite) occurs when someone strikes another person's mouth and teeth with a clenched fist. This results in a wound on the dorsum of the metacarpophalangeal joint.3,4 The bite injury is on the aggressor.

Clenched fist injuries can be severe and may have associated complications. Penetration of the joint capsule, for instance, occurs in 62% of cases and can result in tenosynovitis.3,6 Damage to the extensor tendon needs to be assessed and documented.3 A clenched fist injury can be difficult to diagnosis because patients often will not divulge the true mechanism of its occurrence. Maintain a high level of suspicion for this type of injury when treating patients with a laceration in the metacarpophalangeal region on the dorsum of the hand.

The infection rate associated with human bites ranges from 3% to 50%. Many human bites are already infected at the time of presentation.3

HIV and hepatitis virus can be transmitted via human bites when significant blood exposure occurs. According to CDC guidelines, HIV post-exposure prophylaxis (PEP) is indicated when either participant is HIV-positive or at high risk for the infection.

The risk of transmission of hepatitis B virus is greater than that of HIV. When one of the persons involved is infected, the other, if not previously vaccinated, should receive hepatitis B immune globulin (HBIG), 0.06 mL/kg IM, preferably within 24 hours of exposure, and the hepatitis B vaccine, 1 mL IM, on day 0 and at 1 month and 6 months. The effectiveness of HBIG after 7 days is not known. It is possible to wait for the results of hepatitis serologies if they are rapidly available. If the patient previously received hepatitis B vaccine, no PEP is necessary; however, if the vaccinated patient is known to be a nonresponder, offer HBIG.

There is no PEP for hepatitis C virus; however, it is helpful to identify those exposed to the virus, so they can be tested and observed.4 Check baseline HIV and hepatitis B and C levels every 6 months.3 More information can be obtained from the CDC PEP hotline at 888-448-4911 (Box).

INITIAL EVALUATION

A step-by-step approach to the management of animal and human bites is presented in the Algorithm.

First, obtain a complete history of the incident:

  • Was the attack provoked?
  • What type of animal caused the bite?
  • How did the animal behave?
  • Was the animal domestic or wild?
  • Was the animal vaccinated?
  • Where is the animal now?

The answers to these questions can help determine whether rabies vaccination is needed.4 Follow the requirements of your jurisdiction regarding proper notification of bite wounds to animal control or law enforcement.10 When you take the patient's history, ask about drug allergies, tetanus immunization status, immune status, the presence of prosthetic joints, and other medical problems that might predispose to infection.4

If the patient has not been vaccinated within the past 5 years, administer a tetanus-diphtheria (Td) toxoid booster dose, 0.5 mL IM. For those who have an unclear tetanus vaccination status, who have not received primary tetanus immunization, or who have very high-risk wounds, give a Td toxoid booster dose in one arm and tetanus human immune globulin (250 to 500 IU IM) in the other arm. In these patients, additional Td toxoid booster doses, given 30 and 60 days later, are also indicated.

Examine the patient for other injuries, regardless of the severity of the bite wound. It is not uncommon to focus on the most obvious wound--typically an isolated extremity injury--and overlook other injuries that also need attention. Assess the range of motion and neurovascular function at the wound site. Evaluate all hand bites for tendon injury and wound depth.4 Observe patients for lymphadenopathy and other signs of local or systemic infection.14 Determine the vascular status of the affected area, especially when the injury is on an extremity. If you suspect a vascular injury, consider angiography. Vascular injuries may be seen with any dog that has been trained to bite and hold, especially law enforcement dogs.4

Laboratory tests are typically not helpful unless signs of infection are present.17 Consider radiographs when the wound is on the hand, when the wound is tender or erythematous, and when bony damage or a foreign body is suspected. A radiograph should also be obtained in all patients with infected bites. Look for signs of osteomyelitis or gas in the soft tissue. Air in the joint indicates penetration of the joint capsule.4

WOUND CARE

Immediate care. Irrigate all bite wounds with normal saline or sterile water. If rabies, HIV infection, or hepatitis is a concern, clean the wound with 1% povidone-iodine or other virucidal agent.3 Although these agents may decrease viral transmission, their use is controversial because they may delay wound healing.4,18 In place of a virucidal agent, perform irrigation under pressure. Use an 18-gauge angiocatheter (without the needle) attached to a 50-mL syringe to direct the stream to all areas of the wound to wash out debris. Exercise caution when injecting into tissue, because edema may be worsened.4

Wound closure. A major question is whether to suture the wound. The desire for a cosmetically appealing result must be balanced with the risk of infection. Explain this to patients, so they understand your decision regarding treatment.

In patients who present more than 12 to 24 hours after the bite, leave the wound open, no matter where it is located. Hand wounds--considered high risk because of the relatively poor vascular supply--also should be left open.3 Other fresh wounds can be sutured if properly prepared.

Head and neck wounds can be closed up to 12 hours after the bite. Trunk and extremity (other than hand or foot) wounds can be closed after 6 hours.4 Debride devitalized tissue to remove bacteria and provide cleaner edges.4,17 Cat wounds, in particular, are considered at high risk for infection; therefore, primary closure is not recommended.5 Consider delayed primary closure after 3 or 4 days if no infection is present.4,5 Allowing the wound to heal by secondary intention is also an option.10

Consider referral to a plastic surgeon for patients who are missing tissue in cosmetically sensitive areas. Consult a hand surgeon when a clenched fist injury or tendon damage in a hand wound is possible; these wounds require surgery.4 For other hand bites with no signs of infection, outpatient treatment and close follow-up may be all that is required. Patients with infected hand bites require hospitalization.3

Table 1 - Common organisms that cause bite wound infections

Human
Viridans streptococci
Staphylococcus epidermis
Staphylococcus aureus
Eikenella corrodens
Bacteroides species
Peptostreptococci
Corynebacterium

INFECTED BITES

Infection can result from bacteria either in the mouth of the biting animal or human or on the skin of the victim. Usually, the infection is polymicrobial--with an average of 5 isolates in the wound--and may consist of mixed aerobic and anaerobic species.2,4,11 Obtain cultures from deep within the infected wound.

Signs of infection include fever, abscess, lymphangitis, erythema, edema, tenderness, and purulent discharge.11 Complications of infection associated with a bite include cellulitis, sepsis, endocarditis, osteomyelitis, and septic arthritis.4

Table 1 lists many of the common bacterial species found in bite wounds. Pasteurella species (multocida and canis) are found in 50% to 75% of cat bites and in 20% to 50% of dog bites.5,11 Wounds infected with Pasteurella are purulent, and the infection develops rapidly, typically within 12 hours of the injury.3 Numerous other aerobic species may be found, including Streptococcus, Staphylococcus, Moraxella, Corynebacterium, and Neisseria.5,11 Anaerobic species, Fusobacterium, Bacteroides, Porphyromonas, and Prevotella, cause 56% of infections associated with dog and cat bites. Human bites can become infected with streptococci, staphylococci, anaerobes, and Eikenella corrodens.Eikenella may be resistant to multiple antibiotics; however, it is usually susceptible to the commonly used first-line drugs.4 Unusual species, such as Capnocytophaga canimorsus (formerly known as DF-2), are associated with dog bites.2,3

TREATMENT

When to use antibiotic prophylaxis. This decision depends on the type of wound and the patient's immunocompetence. Prophylactic antibiotic therapy is prescribed for patients with high-risk wounds (bites on the hand, genital region, feet, and cartilaginous structures; human or cat bites; and crush injury or puncture) and for patients with comorbidities, such as immunosuppression and diabetes.3,14

Although controversial, a recent study showed that in a select group of human bite victims (those who were not immunocompromised and who had low-risk wounds that were less than 24 hours old), antibiotics may not be necessary.19 However, for most bites that are not superficial, prophylactic antibiotic therapy is justified.10

Antibiotic selection. Antibiotic prophylactic and treatment options are listed in Table 2. Amoxicillin-clavulanate is the first choice for both prophylaxis and empiric treatment of infection. Second-generation ceph- alosporins can also be considered; however, they are less active against anaerobes. In penicillin-allergic patients, doxycycline is an option, although it is also less active against anaerobes and is not recommended in children younger than 8 years.10 Clindamycin plus trimethoprim-sulfamethoxazole (in children) or clindamycin plus a fluoroquinolone (in adults) can be used in the setting of penicillin allergy.10

Table 2 - Antibiotic choices for prophylaxis and treatment of bite wound infections

BitePrimary AntibioticsAlternative agents

CatAmoxicillin-clavulanate, 875/125 mg bid Amoxicillin-clavulanate, 500/125 mg tid Ampicillin-sulbactam, 1.5 g IV every 6 h Ticarcillin-clavulanate, 3.1 g IV every 6 h Piperacillin-tazobactam, 3.375 g IV every 6 hCefuroxime axetil, 500 mg every 12 h Doxycycline, 100 mg bid

DogAmoxicillin-clavulanate, 875/125 mg bid Amoxicillin-clavulanate, 500/125 mg tid Ampicillin-sulbactam, 1.5 g IV every 6 h Ticarcillin-clavulanate, 3.1 g IV every 6 h Piperacillin-tazobactam, 3.375 g IV every 6 hAdults: Clindamycin, 300 mg qid PO or IV plus a fluoroquinolone (eg, ciprofloxacin, 500 mg bid PO, 400 mg bid IV) Children: Clindamycin (10 - 30 mg/kg/d PO divided q6 - 8h or 25 - 40 mg/kg/d IV or IM divided q6 - 8h) plus TMP-SMX (6 - 10 mg/kg/d TMP PO divided q12h, 15 - 20 mg/kg/d TMP IV divided q6 - 8h)

HumanAmoxicillin-clavulanate, 875/125 mg bid Amoxicillin-clavulanate, 500/125 mg tid Cefoxitin, 2 g IV every 8 h Ampicillin-sulbactam, 1.5 g IV every 6 h Ticarcillin-clavulanate, 3.1 g IV every 6 h Piperacillin-tazobactam, 3.375 g IV every 6 hClindamycin plus a fluoroquinolone or TMP-SMX

Complicated wounds. Hospitalization, intravenous antibiotic therapy, and close observation may be required for patients who are immunocompromised, those who have signs of systemic infection, and those who have joint involvement, multiple bites, or severe local infection. Some experts recommend hospitalization of all persons with infected human bites.14

If sepsis develops, consider unusual organisms; results of previously obtained cultures may be helpful.2 Ask for assistance from your infectious disease colleagues early. A b-lactam or b-lactamase inhibitor, such as ampicillin-sulbactam, ticarcillin-clavulanate, or piperacillin-tazobactam, is the parenteral choice.4,11 Other options include a second-generation cephalosporin or clindamycin plus fluoroquinolone.4,5 Culture results, when available, may be used to modify the antibiotic regimen. However, discussion with an infectious disease consultant would be prudent, especially in a septic patient.

Duration of treatment. Antibiotic prophylaxis is usually administered for 3 to 5 days, while treatment for superficial infections is usually given for 7 to 14 days.5,13,14 For deep infections, which often require intravenous antibiotic therapy, duration of treatment is based on the clinical response.16

Follow-up wound care. Before patients are discharged, provide clear instructions on wound care and schedule follow-up in 1 or 2 days. The wound should be kept clean and dry for 24 hours, and then washed at least daily with soapy water. A splint can be provided in the position of function, with elevation to reduce swelling.4

RABIES PREVENTION

One of the most serious complications of bite wounds is rabies, which causes 30,000 to 70,000 deaths worldwide each year. This viral infection is transmitted in the saliva of infected animals via bite, scratch, or aerosolization and is found in animals throughout the United States, with the exception of Hawaii. The virus attacks nerve tissue and can cause fatal encephalomyelitis.18

Incidence of rabies. The incidence has decreased significantly because of efforts to vaccinate all domestic animals.4 In 1950, there were 18 human and almost 5000 dog cases. In comparison, from 1980 to 1997, there were 95 to 247 dog cases annually and a total of 36 human cases; 21 of these human cases were from bats, with whom contact is a newly recognized risk factor. Twelve cases were from contact with dogs from outside the United States.4,20 The overall risk of rabies infection after a bite from an infected animal is approximately 20%.4

In 2003, 7173 cases of animal rabies were reported to the CDC; 91% were in wild animals, most (98%) of which were raccoons, skunks, bats, or foxes. Domestic animal cases of rabies represented 614 (9%) of those reported. Types of domestic animals in which rabies has been found include dogs, cats, cattle, ferrets, goats, sheep, and swine.5 There were 2 human cases in the United States and 1 case in Puerto Rico.21

To determine whether a patient needs rabies PEP, consider the type of animal bite and the behavior of the animal involved. Once the decision to offer PEP for rabies is made, the procedures are relatively straightforward.

High-risk animals. Skunks, foxes, raccoons, bats, and most wild carnivores are at high risk for rabies. When the offending animal is not available for testing, initiate PEP. Captured animals can be euthanized and examined. In the interim, immunization can be initiated. Small animals, such as squirrels, hamsters, gerbils, rats, mice, chipmunks, and rabbits, are rarely infected because they are less likely to survive an attack from other rabid animals.18,20

Bats represent a special situation, because rabies has been contracted from bats without a clear bite. Rabies PEP is recommended for patients who were bitten or scratched by a bat, as well as for those who find a bat in their bedroom after they wake up.18

Animals that attack unprovoked, that are active during the day when normally nocturnal, or that otherwise act strangely should be considered rabid. Wild animals with rabies may have a complete absence of fear of humans.17

Domestic animals. Domestic dogs, cats, and ferrets that have been vaccinated can be quarantined and observed for 10 days, and PEP for rabies can be withheld.10 In the event of unusual or suspected rabid behavior, the animal should be euthanized, and the brain examined.5,8 When a wound is caused by a domestic animal that is not available and the attack was unprovoked, initiate rabies treatment.5 A provoked attack requires assessment of the situation and careful explanation of the risks and benefits to the patient; however, vaccination is often recommended.

Rabies PEP. Administration of rabies PEP is considered a medical urgency, not a medical emergency. In the ED setting, the first dose of vaccine is typically given during the initial evaluation and treatment of the bite wound. The remaining series can be given in an urgent care setting, the primary care provider's office--if the patient is considered reliable--or through the local public health department.20

Typically, 16,000 to 39,000 persons receive rabies PEP every year. Vaccination is effective when administered appropriately and is comprised of 2 parts: passive and active immunization. The cost is approximately $1000 per patient.18

Active immunization. This involves administration of vaccine to produce neutralizing antibodies. Because it takes 7 to 10 days for these antibodies to form within the patient, passive immunization is also given. The 3 available forms of rabies vaccine are considered equal in efficacy and adverse effects. Rabies human diploid cell vaccine and RabAvert are commonly used. Patients with an allergy to eggs should not receive RabAvert. Administer a total of 5 doses--a 1-mL dose in the deltoid area on days 0, 3, 7, 14, and 28.18

Passive immunization. Rabies immune globulin (RIG) is derived from the plasma of vaccinated donors. It provides rapid passive immunity with a half-life of 21 days, until antibodies form in the patient. The dose (20 IU/kg of body weight ) is infiltrated in and around the wound. Any remaining dose that cannot be given near the bite--because of its anatomic location, eg, a finger--can be given intramuscularly in the gluteus.18 Administer in the upper, outer portion of the glutus to avoid damage to the sciatic nerve.

Adverse reactions to the vaccine are common. Local reactions, such as pain, swelling, erythema, and itching, occur in 30% to 74% of patients. Systemic reactions, including headache, nausea, muscle aches, and dizziness, occur in 5% to 40% of patients. Reactions to RIG include local pain and low-grade fever. Vaccination should not be interrupted or stopped because of adverse reactions.20

For previously vaccinated patients, do not give RIG; instead administer 2 intramuscular doses (1 mL each) of vaccine on day 0 and day 3.18 Pregnancy is not a contraindication to vaccination. In immunosuppressed patients, the immune response may not be adequate. Whenever possible, suspend immunosuppressive medications during vaccination.20

Mortality. Rabies is generally fatal. Worldwide, 5 patients have survived clinical rabies. All patients were vaccinated after exposure but before clinical signs and symptoms developed. Recently, the first recovery from clinical rabies in a patient who was not vaccinated was reported. The patient--a 15-year-old girl from Wisconsin--was bitten by a bat but did not seek medical attention. She received antiviral medications and rehabilitation. The specific treatment protocol will be published shortly.22

For information on rabies and other diseases associated with bite injuries, the CDC has a Clinician Information Line that is available 24 hours a day, at 877-554-4625. The Box provides a list of other resources.

References:

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