Dog Bites

In 2008, one third of American households owned dogs, with a total canine population of 78 million.¹¹² Dog prevalence varies worldwide, and developing countries have a greater percentage of feral domestic dogs. Risk factors for dog bites include the dog’s age, breed, size, medical health, sex, and reproductive status.* Bites are more likely to be delivered by reproductively intact male, large-size (greater than 22.7 kg [50 lb]), 6-month-old to 4-year-old dogs that are mixed breeds, German shepherds, or chow chows. However, breed-specific statements can be inaccurate because of breed popularity and misidentification, inaccurate estimates of a breed’s prevalence, and differences in aggressive behavior.

Of the 800,000 annual dog bites in the United States that require medical attention, approximately 20 are fatal.8,68,128,200,237 Approximately 350,000 emergency room visits related to dog bites occur each year^10,237; the number of admissions is second only to baseball and softball injuries as admissions for recreational injuries. Reports citing large dogs as the most frequent biters may underestimate the number of bites from smaller dogs.²⁴⁴ However, serious bites to children are commonly inflicted by large dogs.^29,83,83 Regardless of size, estimates are that dogs can exert a jaw force of 450 psi, enough to do extensive damage to tissues. Additional pulling and tearing can cause shearing injuries. Dogs cited for causing a high percentage of the severe or fatal bites have included pit bulls, Rottweilers, German shepherds, chow chows, cocker spaniels, and huskies.^155,200,200 However, a study in one Florida county found that golden retrievers and cocker spaniels have bitten more people than German shepherds. Unfortunately, many of these studies on breed prevalence for biting are not adjusted for the relative numbers of breed types in the studied dog population. For this and other reasons, specific legislation that restricts ownership of certain breeds has been questioned.^{46a,171a,174a} In one observation, Labrador retrievers and golden retrievers commonly bit their owners or someone petting them, whereas German shepherds, Bernese mountain dogs, and collies tended to be aggressive toward strangers.¹⁴⁵ Dominance aggression has been linked to unprovoked attacks on people by dogs. In one behavior clinic, the most prevalent breeds for which dominance aggression was treated were the English springer spaniel, cocker spaniel, Labrador retriever, golden retriever, Dalmatian, Rottweiler, and German shepherd.¹⁷² In addition to breed behavior, another important contributory factor to biting is the degree of responsibility exercised by the animal’s owner. Dogs that are less restricted or supervised in their interactions with people are more likely to bite people.^146,170 Certain canine behavioral aggressions related to food, fear, pain, territory, possession, or dominance can increase the risk of bite incidents.

A survey of fatal dog-bite attacks in the United States from 1979 to 1998 listed the pit-bull-type, Rottweiler, German shepherd, husky-type, malamute, Doberman pinscher, chow chow, great Dane, and Saint Bernard as the most prevalent breeds.²⁰¹ These data were acquired by searching news accounts and the Humane Society of the United States registry databank. Dog-bite statistics from media reports in North America show that up to 77% of 931 dog attack fatalities and maimings resulted from dogs that were pit-bull types, Rottweilers, wolf hybrids, or a mix of these breeds.⁴⁴ These data, which may be biased by media interest, show that pit-bull types are the only breed that attacks adults as frequently as children; these dogs may lack normal canine inhibition. In contrast, Rottweilers and other breeds attack children three times more often than they attack adults, indicating that the children’s size may play a role. Wolf hybrids predominantly attack young children (younger than 7 years), suggesting that predation rather than territoriality or reactivity is the reason for their attacks.⁴⁴ Where two or more dogs are involved in an attack, the fatality rate increases. In Canada, dog-bite fatalities, surveyed from media sources, were similarly from owned, known dogs in residential locations with children having unsupervised access to dogs.¹⁸⁴ However, differences from the United States data were those fatal incidents from dog packs in rural locations and higher prevalence of mixed-breed and sled dogs. Furthermore, pit-bull type dogs were underrepresented; however, in Canada they are heavily legislated. Legislation on breed-specific prohibitions in the United States is unlikely to be legally enforceable.²³²

Some are concerned that data from news services may sensationalize and bias reported incidents.¹⁷² Furthermore, the data on fatal attacks should not overshadow the medical importance of nonfatal bite injuries, which likely do not have the same breed bias. Last, dog owners can play a significant role in increasing or decreasing aggressive pet behaviors by the socialization of their dogs and the way they handle aggressive behaviors. No dog is born aggressive, but it can become aggressive through improper discipline and training. Therefore, veterinarians should emphasize and support educating their clients about aggressiveness and legislation directed at controlling undesirable animal behaviors or negligent owners.^{46a,153,171a,174a,240b} Veterinarians should always report aggressive incidents that happen during a pet’s hospitalization to the pet’s owners and others handling the involved pets (Box 51-1). An excellent review of handling aggression in dogs and cats in the veterinary practice has been published.^149a

Less than 20% of dog bites are provoked; males and children are more likely to be involved in provoked attacks.¹⁷⁴ Most dog bites involve a dog owned by the family or a neighbor, and they are often unprovoked. For example, fatal dog bites of newborns often occur when infants are sleeping. Other factors involved with dog bites include the person bitten, the dog-person relationship, and the setting.²⁴¹ Approximately 75% of bite injuries are in people younger than 21 years, with peak incidence at 5 to 9 years. Children are more likely to provoke dogs and often do not understand the dog’s body language. Reports of the high prevalence of bites among children may be related to the additional attention given to dog bites of children compared with those of adults.^51,55,55 Although males make up approximately 65% of all those bitten, boys and girls younger than 6 years account for almost 60% of all fatal bite injuries. More than 50% of injuries among children occur on the head, face, or neck. Any movements in the presence of certain dogs can cause the dogs to become aggressive, especially when children are involved.^141,189 Bending over, reaching toward, hugging, or grabbing the collar of a dog are typical human behaviors that may increase the risk of being bitten, especially if a dog is afraid, possessive, or dominant. Other kinds of dog aggression and their eliciting behaviors are discussed elsewhere.^245,247

In general, humans are more likely to be bitten by a dog if they own a dog, they are in the presence of a dog owned by someone else, or the dog lives in a household with at least one child.83,141,141 Many dogs bite children after an interaction in the absence of adult supervision.¹⁵⁷ Recipients of reported bites are more likely to be neighbors of families who own dogs, with the next likely recipients being the owners, although bites to owners are probably underreported.^29,247

Other factors that can affect a dog’s likelihood of biting include whether the dog is chained for long periods,⁸³ geographic location, time of year, time of day, and weather. A majority of dog bite injuries occur between April and September, when warm weather is conducive to outdoor activity (see Table 51-1).²⁴⁴ Biting incidents have also correlated with increasing fullness of the moon.²³⁸ A booklet on bite prevention is available at www.statefarm.com/consumer/dogbite.htm or www.avma.org. Additional information on dog bite prevention can be found at www.hsus.org. Information concerning variations in dog bite statutes in the United States has been reviewed.⁹⁷ An excellent review on the community approach to dog bite prevention was published in a report by an American Veterinary Medical Association task force.⁹

In a study of dog bites involving caregivers in a veterinary teaching hospital, caregivers interacting with older dogs were more likely to be bitten than those interacting with younger ones.⁵⁹ Dogs with a propensity to bite already had warning signs posted on their cages.

Cat Bites

Compared with dog bites, much less has been reported about feline aggression (biting and scratching) toward people.⁴⁰ Approximately 400,000 cat bites are reported each year in the United States, and cat-induced wounds have a greater propensity for becoming infected than dog-induced wounds. In 2008, one third of American households owned cats, with a total feline population of 88.3 million.¹¹² Cat bites constitute 5% to 25% of animal-related injuries in people, whereas other domestic and wild animals account for less than 1% of reported bites. An epidemiologic study from Valencia, Spain, noted an annual average of 6.36 feline aggression incidents per 100,000 population.¹⁷³

The most commonly reported cat bites and scratches involve unowned female cats that have injured adult women (see Table 51-1). Scratches and bites are more common in warm weather (the summer season) and the late afternoon. Cat-induced wounds have generally been described as being scratches or punctures.²⁴³ The majority of cat bites are provoked by handling cats. Owned cats have bitten people on the neck, face, and multiple sites, whereas strays are more likely to injure the hand. Older humans are more likely to be bitten on the hand.

Bite Wounds

Of the injuries for which medical attention is sought, it is estimated that between 4% and 20% of dog-bite wounds and 20% to 50% of cat-bite wounds become clinically infected.²¹⁶ Clinical infections usually occur within 8 to 24 hours after injury. Dog-bite injuries may result in significantly more functional impairments, although cat-bite wounds have a greater risk of developing a progressive infection.¹³² The small incisors of cats cause deep punctures that can penetrate underlying bones, connective and muscle tissues, and joints. Most bite infections are minor; however, at least 10% require suturing, and between 1% and 5% result in hospitalization.²³⁵

The infecting organism in bite or scratch injuries usually corresponds to the normal oral microflora of dogs and cats (Table 51-2; compare with Table 88-1), although commensal organisms from the environment or skin around the injury of the victim may also contaminate the wound. Bite wounds are usually polymicrobial, with a median of five isolates per wound comprising three aerobes and two anaerobes.^58,216,216 Although more than 80% of cultures produce pathogens, only 15% to 20% of bite wounds become clinically infected.⁸⁹ The risk of infection is highest (approximately 40%) for crush injuries, puncture wounds, wounds in areas of preexisting edema, and hand wounds.⁸⁸ Despite the numerous aerobic and anaerobic organisms that contaminate bite wounds, only a few such as Pasteurella multocida, Neisseria animaloris (formerly designated as Eugonic fermenter-4a), and Capnocytophaga canimorsus consistently cause systemic manifestations. In the past the role of strictly anaerobic bacteria in bite wounds has been overshadowed by such notorious genera as Pasteurella. However, with modern methods of anaerobic cultivation, the role of these bacteria in bite wounds has been realized. When present, anaerobic bacteria are usually isolated in mixed cultures. Fusobacterium spp., Bacteroides species, Porphyromonas species, Prevotella species, and other anaerobic gram-negative bacilli are often involved.^4,124 Erysipelothrix rhusiopathiae has been isolated from dog and cat bites.^1,216 An unusual form of motor neuron disease suspected to be caused by a virus occurred after a cat bite.¹⁰⁹

The public health aspects of rabies, tetanus, and bartonellosis are discussed in Chapters 20, 41, and 52, respectively. Humans who have been bitten may have to be hospitalized if they develop significant local or systemic infections; are unresponsive to oral antibacterials; have penetrating wounds of tendons, joints, or the central nervous system; have open fractures; have significant blood loss or airway injuries; require reconstructive surgeries; require wound elevation; have head or hand injuries; or are immunocompromised.²³⁵

Bacteria Relatively Unique to Dog and Cat Bites

Bite wounds caused by dogs and cats may contain some unique bacteria that have not been previously identified in people. Although some, such as Pasteurella organisms, are commonly found in animal bite wounds, others such as Riemerella anatipestifer in the cat mouth and Bacteroides tectum, which is found in cat and dog bites, are unique to these animals. Eikenella corrodens, a pathogen often found in wounds caused by human bites, has been reported once each as a result of a dog bite and a cat bite.²¹⁶ Corynebacterium canis, a newly characterized species, has been isolated from a dog bite infection.^74a Unfortunately, some of the unusual bacterial isolates described previously may not be responsive to conventionally used antibacterials.

Corynebacterium auriscanis

This organism, which had previously been isolated only from dogs, was isolated from the bite wound of a previously clinically healthy person.³⁵ A newly described member of the genus, C. freiburgense sp. nov., was isolated from a dog-bite wound.⁷⁵

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