Bites and Injuries Inflicted by Wild and Domestic Animals

Chapter 56 Bites and Injuries Inflicted by Wild and Domestic Animals

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Wild and domestic animal bites are distinct from other injuries suffered by humans. Tearing, cutting, and crushing injuries may be combined with blunt trauma caused by falls. Animal bites may cause local infection, and offending bacteria reside in numerous environmental sources. However, few traumatic lacerations are as regularly contaminated with as broad a variety of pathogens as are animal bites. Domestic animal bites are common, and their incidence is rising.43,201,297 Wild animal attacks are often more spectacular; however, in the developed world, injuries from domestic animals have a much greater health and economic impact. Humans are not a preferred natural prey of any animal, and, although some attacks are predatory, most attacks are caused by fear of humans (real or perceived), territoriality, protective instinct, or accident. Unfortunately, wild animal attacks may be sensationalized by the lay press, and animals given anthropomorphic characteristics that do not accurately reflect their instinctive responses; this may lead to public misunderstanding of animal behavior. Press reports may ignore the fact that wild animal attacks are rare and that wild animals are far less likely to cause injury than are their domestic counterparts.

As human settlements and populations continue to grow and encroach on the natural world, the incidence of human–animal encounters will increase. Adventure-seeking humans may also seek out animal encounters that historically would have been avoided. A wolf sighting 100 years ago would have been cause for alarm, yet today people travel to Yellowstone National Park to see wolves in the wild and hope to get close enough to take pictures. The increased pressure of human proximity to animals increases the likelihood of an encounter resulting in a negative outcome (Figure 56-1).40

Other special features of human–animal encounters include attacking animals that may terrorize the victim and transmission of systemic diseases, many of which might cause substantial morbidity and mortality (for a discussion of zoonoses, see Chapter 59). In addition, treatment decisions are often made without a strong scientific basis, and management of wild animal attack victims is often based on a much more robust experience with domestic animal attacks (i.e., dog and cat bites).

It is important to note that animal-caused injuries are usually preventable. When experience allows humans to understand the typical behavior of a species, people can take proper precautions near potentially dangerous animals. For instance, when an animal attacks to defend itself or its territory, it is likely to cease this behavior when the person leaves and the perceived threat is diminished. However, during a predatory attack, the intent of the animal is to kill and not allow its prey to escape. Understanding how to react in these situations decreases the potential for a disastrous outcome. This chapter interprets the present state of knowledge and makes logical and specific recommendations for all of these conditions.

General Epidemiology

According to the 2008 National Pet Owner Survey, 39% of all households in the United States own a total of 74.8 million dogs, and 34% own 88.3 million cats.10 During 1 year in Pennsylvania, county health officials reported 16,000 animal bites, 75% of which were dog related; the highest incidence of dog bite was among children less than 5 years old. Three-quarters of persons injured received wound treatment, and one-half received antimicrobials. Postexposure rabies prophylaxis administration was prescribed for attacks by species as follows: 44% for cats, 30% for dogs, 7% for raccoons, 4% for bats, 2.5% for squirrels, 2.1% for groundhogs, 2% for foxes, and 8% for all other species.230

Each year, dogs bite 1.8% of all Americans, resulting in 4.7 million wounds. More than 750,000 of these victims seek medical attention.75 Bites to children are common, especially among boys between the ages of 5 to 9 years.75 Over the course of 1 year in Pittsburgh, Pennsylvania, 790 dog bites were reported, but an estimated 1388 went unreported; the annual incidence was 58.9 bites per 10,000 individuals.81 Of 279 reported injuries caused by animals to travelers, 51% were caused by dogs, 21% by monkeys, 8% by cats, and 1% by bats.144 In India, where stray dogs cause 96% of rabies cases, the annual dog bite rate is 25.7 per 1000 individuals, and the most common victims are males.3,86

The annual incidence of cat bites in the United States is approximately 400,000.303 A cat bites one in every 170 people each year, and 80% of these bites become infected.156 Biting cats are typically stray females, and most human victims are female.

Of the approximately 30 million Americans who ride horses, 50,000 a year are treated for horse-related injuries in an emergency department, principally because the rider is unrestrained and can fall off while traveling at speeds of up to 64.4 km/hr (40 mph). Horses can kick with a force of up to 907 kg (1 ton), and frequently bite. A 2-year review of animal bites in Oslo, Norway, revealed that horses caused 2% of 1051 recorded bites; 53% of these horse bite victims were children.104

The American Ferret Association estimates that 6 to 8 million domesticated ferrets reside in the United States. The Centers for Disease Control and Prevention (CDC) reports that the number of bites inflicted by ferrets—65 reported bites in 10 years—is substantially lower than that caused by dogs and cats (i.e., between 1 and 3 million)23 (Table 56-1). In Arizona, 11 ferret bites were reported over 11 months; with the ferret population estimated at 4000, the reported bite-to-ferret population ratio is approximately 0.3%.316 The risk of attack by a ferret is greatest among infants and small children.

In Sweden, 3 in 1000 citizens are injured by animals each year.46 Domestic animals accounted for more than 90% of injuries, moose accounted for 6% (almost all were involved in auto accidents), and all other animals accounted for 4%. However, bites were not examined separately, and many injuries occurred during vehicular accidents with animals. Some officials estimate there are two additional bites for every one reported, but a survey of children between the ages of 4 and 18 years old estimated an incidence of more than 36 times the reported bite rate. These figures are most likely based on domestic bites, although this was not specifically stated.32,33 During a 7-year period in Texas, 2% of all large-animal–related trauma was caused by wild animal attacks.243 From 2001 to 2005, there were 472,760 reports by poison control centers of animal bites and stings, which is an average of 94,552 reports per year.202

A 2006 GeoSentinel review of injuries to travelers from 1998 to 2005 showed a total of 320 reported animal-related injuries (i.e., 1.8% of all reported injuries).144 The review revealed that, among travelers, women were more likely than men to be injured by animals. Men were more likely to be injured by dogs, women by monkeys, and children suffered animal injuries at a higher rate than any other travel-related injury. By geographic region, travelers were most likely to experience animal-related injuries in Southeast Asia, followed by Asia, Australia and New Zealand, Africa, Latin America, North America, and Europe.144

Typical Victim

No published reports characterize the typical wild animal attack victim. Two U.S. state health departments report that, if all animal bites (including domestic) are considered, animal bites occur most often among male children between the ages of 5 and 9 years.302,306 However, more than 90% of animal attacks in these states are caused by domestic animals, so this group may not accurately reflect the typical victim of a wild animal attack. In developing countries, many persons are exposed daily to biting animal species that are considered “exotic” in the developed world.

Persons in certain occupations in developed countries (e.g., veterinary and animal control workers, laboratory workers) are at greatest risk for wild animal bites. One study reported that 65% of veterinarians had suffered an animal-related injury during the preceding 12 months.200 The U.S. Bureau of Labor Statistics reported that, during a 5-year period, 186 occupational injury fatalities were caused by animal attacks and that the majority involved cattle.58 In one study of 102 animal control officers, the overall bite rate was 2 per 57 individuals per working day, which is 175 to 500 times the estimated rate for the general population (this study did not differentiate between wild and domestic animal bites).32 The incidence of biting varies with species exposure. In 2003, 93% of Wisconsin and Minnesota veterinarians were victims of dog or cat bites. Cattle and horses inflict the most injuries to veterinarians, with kicking, biting, and crushing being the top three mechanisms of injury.116

In every statistical series of bites, small numbers of exotic animals—including ocelots, jaguars, lions, leopards, polar bears, wolves, anteaters, and weasels—are represented. Bites from these animals occur as a result of exposure to wild and zoo animals and because of the increasing popularity of keeping wild animals as pets. This practice, which commonly involves exotic animals being kept illegally and without adequate training and understanding of animal care and behavior, all too often ends in tragedy.

Several thousand people per year are killed by mammalian bites, with most of the deaths inflicted by maneating lions and tigers in Africa and Asia (Table 56-2). By way of comparison, the World Health Organization estimates that 5 million people per year are bitten and 125,000 killed by snakes and that additional millions are killed by insect-borne diseases.349

An estimated 200 persons are killed by animals in the United States each year; 131 of these die in traffic accidents involving deer.170 Bees kill approximately 43 persons, dogs 14, and rattlesnakes 10. Wild animals (e.g., bears, cougars) kill fewer people than do goats, rats, jellyfish, and captive elephants. More than 3 million people visit the wilderness in Yellowstone National Park every year, but the incidence of serious injuries by bears in the park is less than that of being struck by lightning.162

Circumstances Surrounding and Prevention of Animal Bites: Animal Behavior

Analysis of unintentional injuries shows that these are not random events but rather, are predictable events and have identifiable personal and environmental risk factors similar to those of diseases.350 For example, family pets cause most bites, and the animals are usually provoked in some way. Boys experience 150% to 250% the rate of injuries as compared with girls at every age350 (Table 56-3). Injuries are frequently sustained while playing with the animal.81 Most bites occur in the summer months during the late afternoon. Children sustain a higher percentage of head and neck bites than do adults and are more likely to require medical attention.130 Of all dog bites, 9% to 36% occur to the head and neck region, whereas this area is affected in 6% to 20% of persons who sustain cat bites.130 Understanding such patterns of animal bite injuries allows for improved prevention and treatment.

Prevention of animal bites requires thorough knowledge of the patterns of behavior and personalities of various species of animals. A person who wishes to avoid the bite of a particular species will often be able to gain expertise about that species’ behavior only from those who work with it regularly. Detailed information about animal behavior and the attack patterns of animals is also available on the Internet (Box 56-1).

Basic Principles for Avoiding Animal Bites

Domestic animals of any kind rarely attack unless provoked, although unrestrained dogs are sometimes exceptions. Physical attack is usually a last resort, but an animal will fight if it perceives that it is trapped. Reducing the risk of injury is often based on common sense and knowledge of animal behavior. For example, horses kick backward and with both rear feet, whereas cattle kick forward with only one foot. How a person reacts during a confrontation with an animal is also important. Nonpredator species (e.g., cattle, deer) are very susceptible to human intimidation, whereas a direct stare at a canine may be seen as a challenge.

Expert recommendations can reduce the chance of being attacked and bitten by a domestic animal (Box 56-2). Specific actions can be taken when an individual is threatened or under attack by a dog (Box 56-3). Dogs are guided by memory and instinct; fear and self-preservation are very strong instincts, so any perceived threat could lead to an attack. Territoriality is still ingrained in domestic dogs, even if humans provide for them. Protection of food can cause aggression, even in a docile dog. Any threat to a dog’s mate, offspring, or owner may result in an attack. Personality changes may lead to aggression; causes include illness (e.g., distemper) and physiologic factors (e.g., a female in heat).

BOX 56-2 Advice for Avoiding the Bites and Attacks of Common Pets*

Like their domestic counterparts, wild animals rarely attack humans without provocation. Exceptions are large apex carnivores, which may be relatively unafraid of humans, and creatures infected with rabies. However, carnivores do not commonly hunt humans as preferred prey. The animal’s perception of provocation may not be readily apparent to the inexperienced individual. Patterns of behavior and attack differ by species.

People often capture or restrain wild animals, thereby creating stress that may cause even the most benign animal to attack its captor. Allegedly tame animals are very likely to struggle. Even shy animals that are being captured for treatment of an injury may attack in self-defense and can inflict a life-threatening injury (e.g., goring). Therefore, all situations that involve animal restraint and capture are considered high risk, and careful study of the species’ behavior, the individual animal, and the physical environment and available resources should precede actual attempts at restraint (see Chapter 61).

Because people seem drawn to raising wild animals as pets,211 a large and lucrative market exists, particularly in the United States. No matter how they are raised, these animals remain wild and will never be as predictable, trustworthy, and nonaggressive as animals that have been domesticated for centuries. Often owners of these animals demonstrate a lack of common sense; consider the case of a pet Bengal tiger that attacked and killed its trainer, then did the same to its owner 6 weeks later.21,112

Most wild species have a strong sense of territoriality. Individuals, pairs, and larger groups establish a territory that ranges from square feet to miles and aggressively prevent any intrusion into that territory, particularly by members of their own species. During mating season and later during protection of the nest and young, this drive may stimulate even small animals to threaten or attack humans.

A major principle of animal behavior is that physical attack is often the animal’s last resort. Animals generally give ample warning regarding their intentions. Elaborate rituals and rules that encourage a nonviolent solution so that the victor may successfully defend its territory and itself with little or no injury govern spectacular contests between animals that occur in the wild. Humans can often avoid attack and injury by successfully interpreting visual, auditory, and olfactory warning signs. If a human slowly and carefully backs away without making sudden or threatening gestures, usually no harm will be done. However, the ideal reaction depends on the species. For example, mountain lions have been turned from a full charge by a human who acted aggressively or fought back.35 Given a choice of victims, such a predator prefers the fleeing and panicked victim who demonstrates expected behavior patterns.

If capture of an animal is essential, detailed preparation should be undertaken. For small animals, using nets or heavy cloth and wearing extremely heavy gloves and other protective clothing are advisable. Desperate animals can bite with tremendous force; large carnivores can easily amputate a gloved digit. A wolf can tear apart a stainless steel bowl with its teeth, and a hyena can bite through a 2-inch–thick wooden plank.92 Four men are needed to subdue an adult chimpanzee; an orangutan can maintain a one-fingered grip that an adult human cannot break. Larger animals generally require a team approach by animal control specialists with equipment such as nets, barriers, cages, and immobilizing drugs. Ideal immobilization techniques for various species are detailed in veterinary and wildlife management publications137,142 (Box 56-4).

Evaluation and Treatment of Injuries: Prehospital Care

Attacks by domestic and farm animals are fairly predictable and preventable; this is unlike many attacks in the wilderness. In Africa and Southeast Asia, life-threatening attacks by large animals such as water buffalo, lions, tigers, and elephants are common. Attacks by larger animals can result in major blunt or penetrating trauma, with possible major arterial blood loss, airway damage, broken ribs, pneumothoraces, and intraperitoneal bleeding. The victim’s condition and availability of rapid evacuation determine the extent of treatment in the field. Medical personnel or supplies are often not available, so the victim must be moved to a hospital or clinic as soon as possible.

Many of the complications and serious infections that occur as a result of animal bites are caused by inadequate first aid and delays in medical care. Local wound treatment should be initiated at the scene of the bite (Box 56-5); more than any other therapy, this can determine the course of healing. Simple first-aid measures must be initiated immediately unless definitive or better treatment is available within a short time. Pressure on the wound or pressure points controls most bleeding; avoid tourniquets unless blood loss cannot otherwise be controlled. If the victim is more than 1 hour from a treatment facility, cleanse the wounds at the scene as soon as resuscitation efforts are complete. Early cleansing reduces the chance of bacterial infection and is extremely effective for killing rabies and other viruses. Potable water, preferably boiled or treated with germicidal agents, is adequate for wound irrigation. Ordinary hand soap adds some bactericidal, virucidal, and cleansing properties. If 1% to 5% povidone–iodine in normal saline solution is available, it should be used as an irrigant. Alternatively, thoroughly irrigate the wound with at least a pint of soapy water and then gently debride it of dirt and foreign objects by swabbing with a soft, clean cloth or sterile gauze. Irrigation with a syringe is preferable (see Chapter 22).

BOX 56-5 Summary of Mandatory Animal Bite Wound Treatment for All Wounds

After cleansing, cover the wound with sterile dressings or a clean, dry cloth. Wounds of the hands or feet require immobilization. If the wounds are at high risk for infection, treatment is hours away, and an antibiotic such as amoxicillin–clavulanate (first line), a fluoroquinolone plus clindamycin, trimethoprim-sulfamethoxazole plus clindamycin, amoxicillin plus cephalexin (less effective), azithromycin, or doxycycline is available,1,102,308 then it is reasonable to start immediate treatment with an oral dose (Box 56-6). To most effectively prevent subsequent wound infection, antibiotics should be started within 1 hour of wounding. However, with a severe wound, it is worthwhile to provide the antibiotic, even if delivered substantially later. If antibiotics are unavailable, the wound is infection prone, and medical care is delayed, a simple remedy such as filling the wound with honey may be an effective antibacterial strategy.264 Because of its high osmolarity and weak hydrogen peroxide concentration when diluted, honey can be effective as an antibacterial when used in adequate quantities, although there are no randomized controlled trials to support this recommendation. The wound should be flooded with honey that has been slightly thinned with water and kept flooded like this until definitive treatment is available. The amount of honey needed will depend on the amount of exudate from the wound (because of dilution), and the frequency of dressing changes will depend on how rapidly the exudate dilutes the honey.

Whenever possible, even in prehospital settings, wounds should be cleansed and irrigated thoroughly. Irrigation should be delivered with pressure equal to about 8 to 12 psi and debrided as effectively as possible. For some wounds that are not at high risk, attempting field closure is reasonable, and a loose closure with a dressing may help to decrease bleeding, prevent infection and make self-evacuation possible. However, in general, field closure of contaminated bite and claw wounds is not recommended. Further discussion of bandaging and wound-repair techniques may be found in Chapters 21, 22, and 23.

In addition to treating the bite victim, try to capture the offending animal for examination, if this can be done without risk of human injury in the process. Unusual behavior, such as unprovoked attack by a wild animal in broad daylight or a complete absence of fear of humans, should raise the suspicion for rabies (see Chapter 60). Live animal capture is optimal, but freshly killed animals are usually satisfactory for examination for fluorescent rabies antibody. Avoid damaging the animal’s head and brain (e.g., by gunshot or bludgeoning), because brain tissue is needed for analysis. Availability of the animal can eliminate the need for costly and uncomfortable rabies prophylaxis. If more than 1 hour will elapse before the animal can be transported to a hospital or public health department prepared to process the body for the determination of rabies, then refrigerate the body. For shipping, wrap the animal’s head and transport it in an insulated container with ice or ice packs. Do not use preservatives. Be sure to include the type of animal, details of the exposure, date of the animal’s death, victim information, and a description of the animal’s behavior in the report accompanying the specimen.304 An examination of the animal is not useful for most other diseases and will not help predict local wound infections. Therefore, use good judgment when deciding how much time and energy to expend on capture.

Evaluation and Treatment of Injuries: Hospital Care

Resuscitation with fluids and possibly blood products may be needed if there is extensive volume loss. When considering diagnostic imaging, the type of animal and its particular attack characteristics should be considered. Blunt trauma often accompanies penetrating injuries such as goring and trampling. Animal attack wounds classified as high risk for infection (Box 56-7) include deep puncture wounds, moderate or severe wounds with associated crush injury, wounds with areas of underlying venous or lymphatic compromise, wounds on the hands or in close proximity to a bone or joint, and bite wounds in compromised hosts (e.g., immunocompromised, absent spleen or splenic dysfunction, diabetes mellitus). Surgical consultation and hospital admission should be considered early in such cases.

Wound Management

Animal bites are not clean lacerations, and wounding may be compounded by crush injuries with devitalized tissue. All bites should be treated as contaminated wounds. Evaluate all victims of animal bites for blunt trauma and internal injuries, which may be less obvious than the bite wound (see Box 56-5). Internal organ, deep artery and nerve damage, and penetration of joints are all possible. Particularly in children, animal bites can penetrate vital structures, such as joints or the cranium.53,68 Radiographs may be employed whenever these injuries are suspected. A complete head-to-toe evaluation for trauma is advised in all but the most trivial and isolated bite injuries. Laboratory tests are of little use when evaluating animal bite injuries. Unless hematocrit is being assessed for evidence of blood loss, the complete blood cell count is not useful, because it is a nonspecific and unreliable gauge of infection. Definitive trauma evaluation and treatment are discussed in detail in Chapter 21.

Routine wound cultures obtained at the time of initial wounding do not reliably predict whether infection will develop or, if it does develop, the causative pathogens.135 Therefore, culturing an uninfected bite wound does not yield any useful data.49,60,135 If a bite wound appears infected, cultures and gram staining should be obtained before antibiotics are administered. It is useful to alert the laboratory technician that the culture is from a bite wound, because organisms such as Pasteurella multocida are often misidentified.

Many bite injuries are simple contusions that do not break skin. The infection potential of these injuries is low; superficial wound cleansing and symptomatic treatment of pain and swelling suffice. Treatment should include prompt and liberal application of ice or other cold packs during the first 24 hours. However, this is not beneficial for snakebite (see Chapters 54 and 55), and is obviously impractical in many locations.

When skin is broken, the risks of local wound infection or transmission of systemic disease are incurred. Infection can be caused by organisms carried in the animal’s saliva or nasal secretions, by human skin microbes carried into the wound, or by environmental organisms that enter the wound during or after the attack.225

Debridement removes bacteria, clots, and soil far more effectively than does irrigation.135 In addition, debridement is intended to create cleaner surgical wound edges that are easier to repair, heal faster, and produce a smaller scar. Topical antiseptic ointments (e.g., neomycin, bacitracin, polymyxin) are highly effective for promoting healing of minor skin wounds.146,206 Although topical ointments are appropriate for abrasions produced by animal bites, they may be less effective for punctures and sutured lacerations.

A sutured wound is covered by a simple, sterile, dry dressing to protect it from rubbing against clothing or repetitive minor trauma. Delayed primary closure requires that the wound be kept moist; this is usually done with a wet saline dressing twice daily until closure, which is generally planned for 72 hours after wounding.135

Wound Closure and Infection Risk Factors

Three major considerations govern the decision of whether to suture a wound: cosmetics, function, and risk factors. Cosmetic appearance virtually mandates suturing all facial wounds, which are usually low risk. Similar reasons may dictate closure of wounds on other visible portions of the body. Function is of critical importance for wounds of the hand, a high-risk area in which infection can have disastrous consequences. Thus, in general, all but the least complex hand wounds should initially be left open. Risk factors are many and complex, and provide a useful logical framework for making the decision of whether to suture, administer antibiotics, or undertake other treatments. For more information about surgical procedures, see Chapters 21 and 22.

The amount of time elapsed after wounding is a critical risk factor; the longer the interval, the more likely the chance for infection. After the first few hours, adequate wound cleansing is unlikely to be carried out. In developed countries, many victims are seen within hours of wounding, and the results are usually very good. In remote and undeveloped areas and countries, wounds commonly do not receive medical attention for half a day or more, thereby putting them into a high-risk category that may eliminate the possibility of primary repair. Certain species—including primates, wild cats, pigs, and large wild carnivores—seem to inflict infection-prone wounds. Wounds that involve crush injuries, puncture wounds, hands or feet, or affect a compromised host are at high risk for infection, and primary closure should only be attempted after careful consideration and with surgical consultation and concurrence in most cases. If primary closure is not chosen or deemed too risky, surgical consultation for a discussion of other options, including delayed primary closure or vacuum-assisted closure, is prudent.55,135

Many minimally contaminated bites can be safely sutured after proper wound preparation. Data suggest that carefully selected mammalian bite wounds can be sutured with approximately a 6% rate of infection.84 Two separate studies examining the risk of infection after primary closure reported rates of 7.8% (6 of 92 cases)214 and 5.5% (8 of 145 cases).84 The authors of the latter study concluded that the rate of infection after primary closure was acceptable, particularly if a good cosmetic outcome was needed.84

Optimal conditions for primary repair include prompt medical treatment, which is seldom available in remote and undeveloped areas. In these circumstances, leaving bite wounds open (or with a drain, although this is also controversial) is the more prudent course.

Bites of the Hand

Because hand bites are common and infection can be disastrous,334 the hand is considered at high risk for complications (see Box 56-7). The hand contains many poorly vascularized structures and tendon sheaths that poorly resist infection. The fascial spaces and tendon sheaths of the hand communicate with each other, and movement seals off the wound from external drainage and spreads bacteria and soil internally. Because of the unique anatomy of the hand, thorough irrigation of wounds is often impossible.

Data regarding hand wound infection have been collected mostly from experience with domestic dog and cat bites. From a retrospective study in Oslo, Norway, it was determined that nearly all hand bite wounds healed uneventfully when the wounds were left open, either without antibiotics or with penicillin after wound treatment.104 In another European center, the total infection rate was 18.8% in hand bite wounds; this rose to 25% when the hand wound was closed primarily. The average time from the injury to the first medical treatment was 11 hours in infected wounds and 2 hours in noninfected ones.7

Because of the high morbidity and permanent residual impairment that occurs with hand infections, treating them aggressively is best (see Box 56-5). Hand bite wounds should be irrigated, debrided if possible, and, in higher-risk wounds, initially left open.135,334 Small, uncomplicated lacerations can be repaired within 12 to 24 hours. The hand should be immobilized with a bulky mitten dressing in an elevated position, and the victim usually should be started promptly on antibiotics. Specialty consultation and follow up are mandatory for persons with established infection, and hospitalization should be considered. Persons who are not hospitalized should be rechecked daily until signs of infection clear. In the patient without initial evidence of infection, 5 days of splinting and oral antibiotics should suffice if no complications develop.62 Radiographic examination to search for fractures and imbedded foreign bodies should be considered for all significantly injured extremities.

Facial and Scalp Wounds

Facial and scalp wounds tend to heal rapidly, with little risk of infection; in general, they may be sutured primarily, and do not require prophylactic antibiotics. Typical dog bites of the face and neck (including punctures) have an infection rate of only 3%, even when sutured.7,104,107,342 Generally the cosmetic closure of facial wounds is afforded by the lower incidence of infection. Standard of care in most cases is primary closure of an animal bite wound of the face.342

A major risk associated with facial and scalp wound victims of large carnivores is that the teeth can easily perforate the cranium, producing depressed skull fracture, brain laceration, intracranial abscess, or meningitis.78,260 In young children with such wounds, or in adult victims of large carnivore bites, computed tomography (or in the absence of computed tomography, skull radiography) should be routinely employed to look for evidence of perforation that would mandate immediate neurosurgical consultation and admission to the hospital.

Follow-Up Care

Assuming that the possibility of major or occult trauma has been ruled out, follow-up care for animal bites depends on the risk factors present (see Box 56-7) and the patient’s response to treatment. With only a superficial abrasion, infection is unlikely, and no return visit is needed. With an ordinary low-risk bite wound, one follow-up visit in 2 days to assess any infection will suffice. If the patient is very reliable and no sutures have been placed, a return visit may not be necessary. Infected wounds dictate much closer follow up, with the frequency depending on the wound’s response to treatment and the patient’s risk factors. In a high-risk wound or compromised patient, the initial follow-up visit should be made within 24 hours if the patient is not hospitalized.

Infection: Zoonoses and Rabies

Immense numbers of bacteria inhabit animals’ mouths and can be inoculated into a bite wound. Claw and scratch wounds may be contaminated with soil, urine, and feces. The exact pathogens vary depending on the biting species (Box 56-8). If inoculated in sufficiently large numbers, these microorganisms can cause localized cellulitis and abscess formation, the most common forms of infection. Wild animals also act as vectors for diseases, such as rabies, cat scratch fever, monkeypox virus, simian herpes virus, tularemia, hantavirus, tetanus, Q fever, and toxoplasmosis (see Chapters 59 and 60).


Rabies is discussed in detail in Chapter 60, so comments here are limited to brief remarks about epidemiology, assessment of risk in the bite victim, and local wound treatment.

Rabies is a rhabdovirus that occurs in wild and domestic animals and is transmitted through the saliva of an infected animal. It is generally believed that no true reservoir host exists for rabies (i.e., no species harbors a latent and nonfatal infection).

The epidemiology of rabies varies widely in different parts of the world. In the United States, Western Europe, and Canada, wild animals are by far the main vectors of rabies, accounting for more than 88% of all reported cases from the past two decades.196 In India, 95% of rabies postexposure prophylaxis treatment is the result of bites from stray dogs.86 In recent years, rabies in humans has become an extremely rare disease in the United States, with only two cases occurring in 1997196 and one case in 2001.123 Since 1980, rabies-infected bats caused 58% of the human cases of rabies diagnosed in the United States.196 Of the more than 7437 cases of animal rabies reported in the United States in 2001, raccoons accounted for nearly 40% of the total. Foxes, bats, and skunks accounted for all but less than 1% of the remainder. Hawaii is the only state without any reported rabies.123 Foxes are the primary offenders in Europe; some countries have eliminated rabies in wild populations by using innovative vaccination programs.89

Because of local variations in animal vectors and endemics, consultation with the state or local health department is prudent before a decision is made to initiate rabies postexposure prophylaxis (PEP).196 Although the number of human cases has declined, about 18,000 people per year in the United States receive rabies PEP.134 In the rest of the world, virtually all rabies occurs in dogs. Worldwide, dogs account for 91% of all human rabies cases; cats 2%, other domestic animals 3%, bats 2%, foxes 1%, and all other wild animals only 1%.89,347 However, in the United States and Puerto Rico in 2004, 92% of all rabies cases were attributed to wildlife, with the majority being raccoons, skunks, and bats.196 It is important to note that 75% of animal injuries to travelers occurred in rabies-endemic countries, including Thailand, India, Indonesia, China, Nepal, and Vietnam.144 Each year in India, 25,000 humans die from rabies, and one-half million receive rabies vaccine.310 In Thailand, 50% of human rabies cases occur among children who are less than 15 years old.315 In Africa, Latin America, and most of Asia, dogs are the principal vector, although jackals are also a factor. In South America and Mexico, rabid vampire bats cause occasional human infection. During recent years, disruption of the natural ecology of vampire bats as a result of introducing humans and domestic animals to the rain forest has produced epidemics of rabies. In Israel, wolves and jackals are the chief vectors, and the mongoose prevails in Puerto Rico. In Eastern and Central Europe, the raccoon dog (Nyctereutes procyonoides) is an increasingly common vector.89

Risk of rabies exposure rests on several factors, including the type of animal, its behavior, and endemicity of the country or region in which it is located. The incidence of rabies in local species is important; in the United States, urban dogs and cats, domestic ferrets, rodents, and lagomorphs (i.e., rabbits and hares) are at low risk. Description of the animal’s behavior is sometimes helpful, and is easily evaluated in wild animals because most tend to shun humans. The appearance of a skunk, fox, or bat in an urban setting that has no fear of human beings during broad daylight should raise suspicion for rabies. The incidence of rabies is so high for dogs in some developing countries that rabies PEP should always be given serious consideration.

In addition to situations involving animal bites, contact of mucous membranes with rabid saliva or an animal scratch should prompt consideration for rabies PEP. In the United States and other areas in which bat rabies is endemic, if a person is found in a room with a bat and is unable to reliably report the absence of contact that could have resulted in exposure (e.g., an unattended child, a sleeping or mentally incompetent adult), then rabies PEP should be administered.

Thorough and rapid early treatment of wounds from suspected rabid animals may decrease viral load. Immediately cleanse all bite wounds and scratches with soap and water and a virucidal agent (e.g., povidone–iodine solution).302 Evaluate all persons exposed to a possibly rabid animal for rabies PEP. The CDC guidelines issued in 2009 recommend that, for previously unvaccinated persons, the entire dose of rabies immune globulin [20 IU/kg body weight] should be infiltrated at the wound site, if possible. In the United States, two types of rabies vaccine are currently available: human diploid cell vaccine and purified chick embryo cell vaccine. The chosen vaccine is given in 1-mL doses on days 0, 3, 7, and 14 after exposure. Rabies immune globulin should not be administered to previously vaccinated persons. Persons previously vaccinated should instead receive two 1-mL doses of vaccine (either purified chick embryo cell vaccine or human diploid cell vaccine) given on days 0 and 3.74 Further information about rabies pre-exposure prophylaxis and PEP is provided in Chapter 60.

Other Neurotropic Infections

Although Creutzfeldt-Jakob disease (CJD) is not caused by bites or wounds, oral transmission of this spongiform encephalitis has been reported to result from the regionally common practice of eating the brains of wild goats, pigs, or squirrels (even when cooked). CJD is characterized by progressive dementia, ataxia, and myoclonus, and is untreatable. It is caused by a virus also identified in the brains of domestic sheep and mule deer.187 Chronic wasting disease (CWD) is another transmissible spongiform encephalitis that is found in elk and deer in the Four Corners area of the United States (i.e., where Colorado, New Mexico, Arizona, and Utah meet). Food-borne transmission of CJD has raised concerns that the species barrier (i.e., the difficulty an infectious disease encounters during transmission from one species to another as a result of structural protein differences between the agent and host) may not protect against CWD. In vitro conversion of CWD to a human infective form has been demonstrated, but further studies are needed. Between 2001 and 2003, six people—all of whom died—were identified as having a CJD variant. All were known to have consumed venison from CWD-endemic areas, although strong data linking CJD with exposure to CWD were lacking. The risk of transmission to humans, even in CWD endemic areas, remains extremely low.36 Mad cow disease is discussed in Chapter 59.

Prophylactic Antibiotics

Currently, the weight of evidence does not support use of prophylactic antibiotics for wounds that are not high risk. Many animal bites, human and otherwise, are treated with prophylactic antibiotics, particularly bites to the hands or feet or if the victim is immune suppressed. Human-to-human bites, although outside the scope of this chapter, have similar risks for infection compared with other animal bites. A recent double-blind study of 125 people with superficial human bites showed no statistically significant difference in infection rates between antibiotic and placebo groups.52 A Cochrane Database Systems review of eight randomized controlled trials found no evidence that the use of prophylactic antibiotics is effective for cat or dog bites, except in the case of bites to the hand.225 The use of prophylactic antibiotics is advisable for wounds of the hand; the speed of development, frequency, severity, and complications of hand wound infections can be impressive.135,334 Persons with other risk factors may benefit from prophylactic antibiotics (see Box 56-6). These risk factors include prolonged time from injury to treatment; complex wounds with massive crushing; heavily contaminated wounds; wounds communicating with tendons; fractured bones or joint spaces; or medical conditions such as asplenia, diabetes mellitus, vascular insufficiency, and immune deficiency.

For bite wounds, treatment can begin only after wounding and bacterial inoculation; thus, antibiotics are never truly prophylactic. For major surgery, prophylactic antibiotics are of proved value only in carefully selected high-risk procedures and only if begun before surgery.329 Several controlled studies of dog bite wounds found no significant benefit for using prophylactic antibiotics to treat low-risk facial and scalp wounds.111,206 Other studies recommend the use of prophylactic antibiotics only for high-risk wounds or patients.104,107,155,334,342

To be most effective, prophylactic antibiotics must be administered early. The offending bacteria are already present in the wound when the victim is first seen. Therefore, bite victims who require early antibiotic treatment should be identified promptly, preferably during triage on entry to the treatment facility. The victim should receive immediate antibiotics by protocol; the intravenous route is by far the quickest. The current recommendation for duration of antibiotic prophylaxis is 3 to 5 days (see Box 56-6).

Therapy should be tailored to the largest variety of most likely pathogens for a particular type of bite. For most terrestrial mammals, the choice of antibiotic is based on experience with human, dog, and cat bites. However, with an alligator or crocodile bite, or other wounds incurred in freshwater, antibiotic choice should be directed against Aeromonas hydrophila174,226 (see Chapter 58).

Tetanus Prophylaxis

In the United States, cases of human tetanus from animal bites exceed cases of rabies infection by a ratio of 2 : 1 each year.30 The spores of Clostridium tetani are ubiquitous in soil, on teeth, and in the saliva of animals; therefore, the risk of tetanus may be present from any animal injury that penetrates the skin. Rates of tetanus vaccination are highest in the developed world and fall dramatically in the developing world, with Somalia and Samoa having the lowest rates.346,348 For adults in the United States in 2007, the CDC reported that, out of a sample of 3525 people, 2.1% had received a tetanus booster (tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis) in the past 2 years, and the vaccination rate for tetanus during the prior 10 years was 57% (n = 1727).26,77 Because tetanus is preventable and many persons still do not receive tetanus immunoprophylaxis in accordance with guidelines, proper emergency prophylaxis against tetanus remains an important but often underaccomplished intervention (Table 56-4).

For a clean wound that contains little devitalized tissue and that can be easily irrigated and debrided, a previous full course of tetanus immunization plus a booster within the last 10 years is sufficient. For a deep puncture or wound with much devitalized tissue that is difficult to irrigate and debride (which is thus predisposed to anaerobic growth), a full series of previous immunizations plus a booster within the last 5 years is sufficient. If there is any uncertainty regarding the status of the victim’s prior immunizations, 0.5 mL of diphtheria–tetanus or tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis booster vaccine should be administered. A high-risk wound should also prompt consideration of administration of an intramuscular injection of 250 to 500 units of tetanus human immune globulin.

General Complications

Wound infection is generally diagnosed on the basis of increasing redness, swelling, and tenderness of the wound margins that eventually progresses to production of pus, cellulitis, lymphangitis, and local lymphadenopathy. Lymphadenitis and lymphangitis, which are much less common, occur as local defenses are overwhelmed. Symptoms of systemic infection are rare and suggest bacteremia or sepsis.

Wound infection from animal bites should be treated like infection of any other traumatic wound. Elevate the wound, immobilize the affected part, remove sutures or staples if present, and provide antibiotic therapy (see Box 56-6). The 1999 Emergency Medicine Animal Bite Infection Study Group findings recommended that empiric treatment include a combined β-lactam/β-lactamase inhibitor antibiotic, a second-generation cephalosporin with anaerobic activity, or combination therapy with either penicillin and a first-generation cephalosporin or clindamycin and a fluoroquinolone.135,314 Additional studies recommend azithromycin, trovafloxacin, or telithromycin, which demonstrate good in vitro activity against unusual aerobic and anaerobic animal pathogens.150152314 In 2002, a study showed that garenoxacin, a des-fluoro(6) quinolone, was very active against 240 aerobic and 180 anaerobic isolates from bite victims. It inhibited 403 of 420 (96%) isolates, including those of Moraxella spp., CDC group EF-4, Eikenella corrodens, all Pasteurella spp., and Bergeyella zoohelcum. Fusobacterium russii and 6 of 11 Fusobacterium nucleatum isolates of animal bite origin were resistant.153

Extremely rare pathogens can cause infection (see Box 56-8). Culture of debrided tissue is the only reliable identification technique, and sensitivity testing may take weeks. In 2002, a 7-year-old girl developed a wound infection as a result of a tiger bite; DNA sequence analysis revealed that one of the causative organisms was a previously undescribed subspecies of Pasteurella multocida, which the authors designated “Pasteurella multocida subspecies tigris.63 This organism is usually sensitive to ciprofloxacin, cefoxitin, and perhaps rifampin.266 A diabetic patient developed tenosynovitis caused by Mycobacterium kansasii after an accidental bite by his pet dog,305 and Bergeyella zoohelcum has been reported as a fastidious species that is difficult to culture from patients with infected cat bites.294

Septic Complications

Bacteremia and sepsis, although theoretic risks with any animal bite pathogen, have so far been reported with only a limited number of species.9,133,197,260 Clinical manifestations include cellulitis, endocarditis, meningitis, pneumonitis, Waterhouse-Friderichsen syndrome, renal failure, shock, and death. Purpuric lesions are seen in one-third of cases and may progress to symmetric peripheral gangrene and amputation. House cats are an increasing source of human plague in the Southwest United States. Since the onset of the human immunodeficiency virus epidemic, Rochalimaea infection (bacillary angiomatosis) has also become more prominent, and is closely associated with exposure to cats. Although sepsis after an animal bite incident is reported more often among immunosuppressed patients (e.g., there was a case of fatal Pasteurella dagmatis peritonitis and septicemia in a patient with cirrhosis188), there are reports of fatal cases of purpura fulminans with gangrene, sepsis, and meningitis caused by Capnocytophaga canimorsus among previously healthy patients after dog bites. 109,204

Allergic Reactions

Up to 11% of laboratory workers have allergic reactions to laboratory animal dander, hair, or urine.343 One case of proved hypersensitivity to rat saliva after a bite has been reported.157 The patient was subsequently proved to be allergic to the saliva (presumably to saliva proteins) and not to other portions of the rat. The bite produced lymphangitic swelling and itching that subsided within 24 hours. Two cases of anaphylaxis after dwarf hamster bites have also been reported.241

Psychiatric Consequences of Animal Attacks

Victims of traumatic or life-threatening events may develop posttraumatic stress disorder (PTSD). This syndrome has been recognized by the authors as a result of wild animal attack, and is rarely reported in the scientific literature.108 After physical recovery from an attack, the victim may be plagued by recurrent nightmares and flashbacks of the event and may have an aversion to outdoor travel. Violent and multiple attacks or those associated with deep bites have a higher probability of causing PTSD symptoms.262 Critical incident stress debriefing and post-trauma intervention counseling may be important aspects of care for victims of animal attack.108 PTSD has been described among children who are victims of dog bites.262 In a 2004 study, 12 of 27 pediatric patients developed either complete or partial PTSD as a result of dog bites.262

Wild Animal Attacks

Neither the annual number of wild animal bites nor the base human population at risk can be reliably estimated, especially when the human population to be considered is only that exposed to a wild animal or in a wilderness setting. The world supports approximately 5500 species of mammals, 10,000 species of birds, and 9000 species of reptiles. The actual number of wild animals in the world is estimated to be in the billions. Many people who suffer relatively minor injuries caused by wild animals do not seek medical attention unless infection or another complication occurs or they fear exposure to rabies. If the injury is minor, patients are generally treated, released, and unrecorded. The following sections consider published data and species-specific information to discuss the prevention of attacks and care for human victims of attacks.


There are approximately 35 species of wild canines, and they are present on every continent except Antarctica. Dingoes, found in Australia, are technically not wild canids, but they are descended from dogs.


Coyotes (Canis latrans) have not only survived the onslaught of civilization in the United States but have thrived and multiplied. Perhaps as a result, more and more coyote attacks on people have been reported, even in urban areas such as Los Angeles.16,64,177 Most of these incidents occurred in Southern California near a suburban–wildland interface. One study done in 1982 was intended to show the coyote density at such a location. Traps were set for the animals within a one-half mile radius of a particular residence, and 55 coyotes were trapped during an 80-day period.176 Between 2004 and 2007, 541 coyotes were removed on average from Illinois; 312 were from the Chicago area alone. It is estimated that there are 1250 coyotes in the suburban area surrounding Washington, DC.311

Between 1998 and 2003, there were 41 coyote attacks on humans in California, and most were unprovoked; it appears that nonrabid coyotes are becoming more aggressive with humans.79 Rabies is less prevalent among coyotes and foxes with the advent of an oral rabies vaccine for these species.295

Attack incidents are typically preceded by a sequence of increasingly bold coyote behaviors. These may include nighttime coyote attacks on pets; sightings of coyotes in neighborhoods at night; sightings of coyotes during the morning and evening hours; attacks on pets during daylight hours; attacks on pets on leashes; chasing of joggers and bicyclists; and midday sightings of coyotes in the vicinities of children’s playgrounds318 (Figure 56-2, online).

Since the 1970s, more than 100 coyote attacks on humans have been recorded in Southern California, with one-half of these incidents involving children who are 10 years old or younger.79 There is one well-documented fatality of a child in 1981, who, despite being rescued by her father, died of blood loss and a broken neck.79 A 5-year-old boy in Middletown, New Jersey (about 64.4 km [40 miles] from New York City) was bitten by a coyote and required 46 stitches to his head.311 A 19-year-old woman was killed by two coyotes (likely coyote–wolf hybrids) in Nova Scotia, Canada while hiking on a trail in October 2009; the woman died of blood loss from multiple bite injuries, and, although one of the animals was wounded, neither coyote was captured.157

The safe environment provided by a wildlife-loving public, which rarely displays aggression toward coyotes, is considered a major contributing factor to the increasing numbers of attacks.79 There has been an increase in reports of coyote attacks in national parks by animals that are subsequently captured and found to be disease free.64

A coyote bite should be treated as a dog bite with respect to antibiotic choice and closure issues; if the animal cannot be captured and examined, rabies prophylaxis should be undertaken. Coyotes have been identified as the reservoir for the human pathogen Bartonella vinsonii sub sp. berkhoffii.80


The gray wolf (Canis lupus), also known as the timber wolf, is the largest wild member of the Canidae family (Figure 56-3). There are an estimated 7000 to 11,200 gray wolves in Alaska and more than 5000 in the lower 48 states. Worldwide, the wolf population is estimated at 200,000 in 57 countries.106

Wildlife experts suggest that attacking wolves are habituated to humans and human food sources. However, most unhabituated wolves are traditionally timid. Historically the majority of predatory attacks occurred during the summer months, and victims were predominantly women and children. Predatory attacks by wolves against humans tend to occur in clusters, indicating that human killing is not normal wolf behavior but rather specialized behavior that single wolves or packs develop and maintain until they are killed.335

Throughout Europe and Asia, wolves have well-documented histories of cunning behavior, pack attacks, and human killing.209 In one Indian state, 100 children were injured and 122 killed between 1980 and 1986.274 Between 1840 and 1861, Russia reported 273 nonrabid wolf attacks, resulting in the deaths of 169 children and 7 adults.194 North America has fewer verified cases, although recent research indicates 80 events in Alaska and Canada during which wolves closely approached or attacked people (there were 39 cases of aggression by apparently healthy wolves and 29 cases of fearless behavior by nonaggressive wolves).208,224 Five wolf attacks on humans occurred within a 12-year period in Algonquin Provincial Park in Ontario, Canada, and a kayaker was pulled from his sleeping bag by wolves in British Columbia, Canada.208 In 2005, a hiker in Northern Canada was eaten by wolves, although he likely died of other causes.121,145 Most recently, in March 2010, a woman was killed by wolves in Alaska in what is thought to be the first known fatal attack by wolves in the United States in modern times.235 Villagers in the area had noted increasing aggression from local wolves preceding the attack; wolves are the only large predator in the region, and had been entering the villages at night and frequenting the edges of settlements.

A substantial number of attacks by rabid wolves in Iran over a 10-year period provided the clinical population upon which the human diploid cell vaccine for rabies was tested.24 The reintroduction of wolves to wild habitat in the Yellowstone ecosystem and Idaho in 1995 has resulted in the successful proliferation of many new wolves. However, there has not yet been a negative human interaction since their release.158

Comparison of victims of fatal attacks by domestic dogs and wild wolf packs reveals distinct differences in bite-mark patterns; the necks and faces of domestic dog attack victims were the primary sites of injury, whereas a wolf-pack victim was spared damage to the neck but had facial tissue destroyed postmortem. Most punctures are found on the ventral aspect of victims of domestic canine attacks as opposed to dorsal punctures among victims of wild or feral canines. Wild canine bites involve characteristic crushed and macerated tissue and should be debrided carefully. Other treatment should follow the same guidelines as for victims of domestic canine attack. It is speculated that most wounds are attributable to the dominant animals of a pack. Differences in bite-mark patterns may be attributed to differences in genetics, training, breeding, socialization, and impetus of attack between wolves and dogs.344


Most human attacks by foxes are inflicted by rabid animals; fox bites have caused eyelid lacerations among children who are sleeping in tents and leg punctures among adults.195,313,327 One child died of rabies from fox bites despite appropriate PEP.313 A rabid gray fox bit several people during a single afternoon in 2008 in Arizona.14 Foxes can cause more puncture wounds than other canines, making their bites more prone to infection. Oral vaccination of fox populations has led to a decline in the number of rabid animals.295

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Sep 7, 2016 | Posted by in EMERGENCY MEDICINE | Comments Off on Bites and Injuries Inflicted by Wild and Domestic Animals

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