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.

Puncture Wounds

Punctures may occur as a result of biting, clawing, or goring. The infection rate is related to difficulty irrigating properly and degree of contamination, which is highest in bites. Puncture wounds can be contaminated with pieces of the victims’ clothing or shoes as well. Usually, attempts to irrigate narrow punctures simply result in rapid development of tissue edema from infused irrigant solution, which does not cleanse the wound. However, if the wound is large or can be held open wide enough to permit fluid to escape, irrigation is worth the effort. Large goring-type puncture wounds up to 20.3 cm to 25.4 cm (8 to 10 inches) deep from bison have a low incidence of infection when closed primarily after irrigation and debridement.⁹⁶ For most smaller puncture wounds, irrigate or debride them as well as possible, suture only if cosmetic or functional considerations require it, and treat as having a high risk of infection.¹³⁵ Use delayed primary closure liberally.

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

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.

Indications for Wound Culture

Culture of fresh animal bite wound surfaces, whether judged quantitatively or qualitatively, is useless as a predictor of infection. Some of the pathogens of greatest concern (e.g., genus Eikenella) can take 10 days to grow out in culture, by which time most therapeutic decisions have been made. Other organisms (e.g., genus Pasteurella) are fastidious, hard to identify, and frequently missed by laboratory technicians, who rarely encounter them.¹⁵⁰

If a wound is infected or if animal bite sepsis is suspected, obtain wound cultures to guide subsequent antibiotic therapy. In certain cases, cultures should be sent to reference laboratories, such as those in state health departments or at the CDC in Atlanta, Ga, because reference laboratories have successfully isolated more pathogens on identical samples sent simultaneously to both reference and local laboratories.³¹⁴

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 hydrophila^174,226 (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).

TABLE 56-4 Wound Management and Tetanus Prophylaxis

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.^150–152314 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

Canines

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

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).

FIGURE 56-2 A hiker at a trailhead bitten on the foot by a coyote while napping.

(Courtesy Luanne Freer, MD.)

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

Wolves

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

FIGURE 56-3 Yellowstone wolves.

(Courtesy Rick McIntyre.)

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

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