Karen L. Overall, MA, VMD, PhD, DACVB, ABS Certified Applied Animal Behaviorist
Center for Neurobiology and Behavior, Psychiatry Department - Penn Med Translation Research Laboratory, Philadelphia, PA, USA
Incidence of dog bites: As of 2000 there were are approximately 52.9-58.2 million pet dogs in the United States in about 35% of all households. Reports estimating the incidence of dog bites vary widely in their findings, with estimates ranging from 0.5-1 million bites per year in the late 1950s through the early 1970s to 3.5-4.7 million bites per year from the late 1970s through the 1990s. Data for other countries, when available, are similar.
The proportion of dog bites that are reported to medical or legal authorities appears to be low: published estimates range from 10 to 50%. To the limited extent that the frequency of medically treated bites can be used to estimate the frequency with which bites are reported, only about 17% of dog bites are reported. Estimates indicate that approximately 17-18% of all bites receive medical attention and that approximately 1-2% of all bites require hospitalization. Dog bite related injuries comprise approximately 0.4-1.5% of all emergency department visits, 1.2% of all surgical cases seen in emergency departments, and 0.3-1% of all pediatric emergency room visits. Dog bite related injuries comprise approximately 3.6% of emergency department visits by male children between ages 5-9 years.
Information about factors that affect dog bites may be biased because of the heavy reliance on data from bites that receive medical attention. The nature and magnitude of these biases is unknown and will remain so until more systematic studies are conducted. Unfortunately, the most complete data are from cases that receive medical and, or surgical treatment. The focus for these cases is on age of victim, type of dog, ownership status of dog, and type of human injury sustained, rather than on the behavioral circumstances of the bite. Few data on canine and human behaviors or bites are collected in a manner that allows critical comparison. Such deficiencies in the available data should be addressed in future veterinary studies (1).
Demographics of Dog Bites
Effect of Victim's Age
The type of human injury incurred in the context of a dog bite depends on physical attributes of both the human and the dog. With few notable exceptions, available studies generally do not define what constitutes a "bite", and do not distinguish between minor injuries like bruises, and more severe injuries, like punctures and lacerations. Data from reported bites requiring medical attention indicate that the majority of dog bites are to children under the age of 15 years. Once a child becomes 1 year old bite incidence increases through 5-9 years. Children are bitten 2-3 times more frequently than would be indicated by their population representation, were all bites distributed equally over victim class. Estimates suggest that by the age of 11 the majority of children have been bitten by a dog, generally one known to them. Children are at least 3 times more likely to experience a medically attended bite than are adults, and 48% of dog-bite related emergency room visits at one center were from children under 10 years.
Effect of Victim's Sex
There are 3 types of studies available that examine the association of sex of the victim and propensity to be bitten: those that present actual data that allow relative risk to be calculated, those that report only calculated relative risk or odds ratios, and those that report the incidence of bites without population level data that permit the calculation of relative risk. Studies that present actual data are the most valuable and represent the type of data future veterinary studies should endeavor to collect. Detailed data that allow a comparison of the relative risk of dog bites for males and females are available from 4 studies: males are bitten significantly more frequently for than are females for all age groups examined in each of these studies.
Dog bites to human males are reported 1.4-3 times more frequently than are bites to females. The proportion of males bitten compared with females ranges from 1.5:1 to 1.7:1 in a population where males outnumber females 1.2:1. Proportions of bites to male children compared with female children varies with age of victim: boys outnumber girls 1.6:1 in the less than 4 year age group and 2.3:1 in the 4-16 year age group. When compared with bites to females 19 years or older (relative risk = 1.0), males 19 years or older have a relative risk of 1.9, females 0-18 years have a relative risk of 4.2, and males 0-18 years have a relative risk of 5.4. This pattern suggests an interaction between age and sex that is also apparent in other geographic and cultural locales.
Finally, males comprise a significantly larger proportion of victims involving dog bite-related fatalities than do females.
Relationship of Dog to Victim
The vast majority of bites in the United States are inflicted by owned, pet animals, not by strays. The family dog is involved in 25% to 33% of the bites. Free-ranging, owned dogs may be more aggressive than strays when approached, and may be more aggressive when closer to home. One excellent study reported that, only for dogs identified as "pit bulls" (P <0.001), were the majority of bites attributable to freely roaming animals that did not belong to the person bitten.
In 96 dog bites for which data on domain in which the bite occurred and relationship of the victim to the dog were available 54% (52) of bites involved victims less than 15 years, 85% (82) of bites occurred in the dog's own home, and 62% (28/44) of adult victims were bitten by their own dog, where as 75% (39/52) of child victims were bitten by dogs belonging to neighbors or friends. Such data strongly suggest that human behaviors may be implicated in dog bites.
Bites inflicted by strays (50.3%) are more likely to be examined by a physician than are bites from family pets (29.1%). It is important to realize that not all stray dogs are unowned. Many "strays" are owned dogs that are allowed to run free.
Victims' Behaviors and Dog Bites
Human behaviors factor into the circumstances initiating a bite and contribute to the amount of damage done. Children aged 5 or younger are significantly more likely to provoke animals prior to injury than are older children (P <0.001).
Most dog bites, particularly to children, occur in the summer, most bites occur on weekends, and the diurnal peak in bite activity is in the late afternoon and early evening. Most children hospitalized for dog bites are bitten on weekends. The temporal environment matters because children are more likely to come into contact with dogs at certain times. The physical environment also contributes to the circumstances of the bite. More children and dogs are outdoors and active during the periods listed. The greater the number of both children and dogs, the greater the potential reactivity of each group. Again, there are no objective measures of this, but empirical evidence from pack situations for both dogs and people (mobs at soccer games, et cetera) indicates that the more excited any participant, the less stable and predictable the situation. Such circumstances are ideal for unilateral or joint misinterpretation by the participants of any signaling behavior. Proximity facilitates violence, rather than retreat, as a response in such conflicts.
In the case of canine aggression towards children, there are two participants with enough overlap in patterns of sociality that it is possible to misunderstand the extent to which the same signal has two different messages and meanings. Just as humans can misinterpret a wagging tail, dogs can misinterpret a screaming child. Children may be uncoordinated and may appear unpredictable to dogs because of their sudden shifts in postures and vocal range when excited. Some behaviors and some intensities of behaviors in young children can frighten dogs. Other behaviors, like shrill squealing, could be misinterpreted by the dog as sounds and signals given by prey. Excitable states facilitate misunderstanding by making all participants less aware of changes in signaling and interactive behaviors. The potential for bilateral misunderstanding and inappropriate reaction with concomitant disastrous circumstances is particularly great for children who may not have the sophistication or maturity to correctly interpret and react in rapidly changing interactions.
Conclusions: Issues of Fact and Dangerous Myth
An extensive literature review (2) of the literature about dog bites revealed that the only robust data are those supporting the following conclusions:
1. There is a substantially greater injury and fatality rate for children when compared with adults.
2. Male children are injured and killed more frequently than female children, suggesting that human behavior may be a significant issue.
3. There is a preponderance of owned, family dogs in those involved in bites and fatalities.
Robust conclusions regarding breed cannot be drawn. The breeds most frequently involved in dog bites at present are mixed breeds, German shepherds, German shepherd crosses, pit bull terriers, and pit bull crosses; the latter four groups are most frequently implicated in fatality.
A careful reading of the literature supports 3 conclusions regarding breed.
1. The breeds most represented in the dog bite data change rank with time. This may indicate changes in breed preference by owners, rather than changes in breed specific aggressive tendencies per se.
2. The breeds most frequently represented in the published data are popular ones and no one breed may be represented in the bite data in disproportion to its occurrence in the population. Good data on population size of each breed and mixed breeds for the human victim populations studied are unavailable, but essential if any legitimate statements about breed over-representation are to be supported.
3. The term "pit bull" is widely applied, often without biological basis, to a range of dog types, regardless of the underlying genetic stock. This latter problem is probably magnified in areas that have already experienced one publicized "pit bull" related attack.
So, are dog bites a problem? Yes, but even with this extensive review of the data, we know little about the actual behaviors of dogs involved in bites, regardless of breed. If we wish to understand why dogs bite and to minimize morbidity and mortality associated with bites, the following goals must be met.
1. The prevalence of dog breeds, and ages, sex, and reproductive status within those breeds, needs to be established within the demographic population for which bites are to be investigated. Any discussion of breed specific aggressive propensities must be critically viewed. Caution is urged regarding any generalizations about inappropriate breed based behaviors. It is best to view selection for specific behaviors as a risk assessment analysis: breeds that have been selected for one or a few particular and specific behaviors may be more at risk for developing undesirable variation for those behaviors. This does not mean that dogs selected for protective behaviors are more aggressive than dogs for which this selective pressure was absent. It does mean that that breed may be more at risk for developing a disproportionate number of dogs who exhibit inappropriate, out of context protective aggression given the selection/breeding conditions outlined above. Inherent in this concept is that any dog, regardless of breed, can also exhibit the inappropriate behavior. A further corollary is that dogs who are selected for tenacity and jaw strength in their in-context work (bull terriers, rottweilers, Rhodesian ridgebacks), will, when they respond inappropriately or out-of-context in another behavioral setting, exhibit this same tenacity. Coupled with the physical traits attendant with such selection (large jaws, heavy musculature), they can and will do large amounts of damage on a first strike. These factors, rather than increased breed-specific aggression, are the cause of the severity of wounds, when inflicted. More research about all of these factors is needed.
2. Canine and human behaviors that limit or exaggerate relative exposure need to be defined and quantified. Any dog breeder or owner who accepts the occurrence of inappropriate aggression or who feels that such aggression is "normal" for their breed, or not dangerous because the dog is small, is contributing to the problem.
3. We need to know which dogs bite and whom do they bite. We must develop specific behavioral profiles of dogs that do and do not bite, and of their owners' behaviors, within the specific population in question. Such studies will indicate whether dog bites are associated with and attributable to a behavioral diagnosis involving aggression, and the extent to which certain human behaviors foster aggression.
4. The situation in which the bite occurred needs to be thoroughly, rigorously, and consistently reviewed and documented by health care personnel in a repeated manner using validated assessment tools, so that the appropriateness of the situation, the extent to which provocation may have been involved, the nature of the provocation (1), and the behavioral propensities of the dog (including whether the dog has a behavioral diagnosis) can be evaluated. This aspect is particularly important, given the association between dog abuse and child abuse, and the extent to which violent behaviors are learned and practiced.
Achieving these goals will require a tremendous amount of work, and anyone who is serious about dogs--especially the AKC--should have a vested interest in seeing projects that address these issues get funded, accomplished, and published. In the absence of actual numerical demographic data, conclusions and discriminatory legislation based on breed are being drawn from, at best, incomplete, and at worst, skewed data and are premature. These data suggest that initiatives like those mounted by the AVMA, HSUS, State Farm Insurance Company, and many other groups to teach children how to interact appropriately in specific situations involving dogs, particularly unfamiliar dogs, may be addressing only the exceptional situation. If this is true, such initiatives will be of extremely limited benefit in reducing the overall numbers of dog bite-related injuries and fatalities. Regardless, widely disseminate application of knowledge about age-associated child and dog behaviors can only help, and veterinarians must take an active role in this aspect of public health care and education (3).
The dog bite issue is so heavily burdened with emotion and rhetoric that we must take extra care to employ scientific reasoning and methodology in the debate. A review of the data to date indicates that popular and numerically dominant breeds are most frequently involved in bites, bites to children are relatively common, most bites to children are to male children, and most fatal dog bites involve male children. No matter how incomplete the data, we still have better data on the children than on the dogs or the behaviors surrounding the bite. To outlaw some breeds, especially in the absence of the needed information discussed, would not make us safer, and the illusion that it would is a dangerous one. To refuse to collect these data is to abdicate our responsibility as scientific professionals. Accurate data can help us to be better guardians of our pets and patients, to raise our children to be responsible and humane with pets, and to become better, kinder, and more humane, ourselves.
Most of these notes were adapted and updated from reference 2.
1. Bollan J, Caudron D, De Keuster T, et al. Les Enfants victimes de morsures de chien. Ms. 2002.
2. Overall KL, Love M. Dog bites to humans: demography, epidemiology, and risk. J Am Vet Med Assoc 2001; 218: 1-12.
3. Love M, Overall KL. Dogs and children: how anticipating relationships can help avoid disasters. J Am Vet Med Assoc 2001; 219: 446-453.