Prevalence and circumstances of dog bites in Poland – a longitudinal study

doi:10.21203/rs.3.rs-1897249/v1

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Prevalence and circumstances of dog bites in Poland – a longitudinal study

https://doi.org/10.21203/rs.3.rs-1897249/v1

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Most animal bites in humans are caused by domestic dogs, making dog bite-related injuries a serious public health and safety concern globally. However, till date there is no comprehensive research regarding the occurrence of dog bites, and incidence of exposure to rabies post-exposure prophylaxis in Poland. Thus, the main goal of the study was to examine incidents of dog bites in humans and the potential risk of rabies in Poland between 1994-2018. Our results showed that the mean annual dog bite incidence rate in Poland was 13 people per 100000 inhabitants, with ~5000 people vaccinated annually post exposure. Children were more likely to be bitten than adults, and males were more likely than females. People were more likely to be bitten by mongrels followed by German Shepherds. However, most of the bite incidents included dogs that were free-ranging or stray, highlighting the difficulty in regulating the vaccination status of the dog and consequently the likelihood of people meeting a rabid animal. Therefore, we recommend increasing stray dog captureefforts to decrease the incidence of dog bites and potential exposure to rabies. Furthermore, official reporting of all cases of dog bites by associated stakeholders involved in data collection would be effective.

Health sciences/Diseases/Infectious diseases

Health sciences/Health care/Public health

aggressive breeds

Canis lupus familiaris

post-exposure prophylaxis

rabies

vaccination

Domestic dogs (Canis lupus familiaris) are responsible for the majority (80–97.8%) of all animal bites to humans ¹, and dog bite-related injuries remain a serious public health and safety concern around the world ^2,3. For example, dog bites are one of the main causes of non-fatal human injuries worldwide ^4,5. According to the World Health Organization (WHO), the number of people injured by domestic dogs likely reaches the tens of millions each year ^6,7. For example, in the United States alone, 4.5–4.7 million people, or 1.5% of the total population, are bitten annually ^3,8,9.

Generally, most bites are caused by dogs known to the victim, i.e., dogs owned by family or friends, and up to 90% of all cases occur at home ^10,11. Breeds with aggressive dispositions are likely to be an important contributor to the high incidence of dog bite cases. Although the majority of dog bite incidents involve crossbreed dogs ¹², research suggests that certain dog breeds are more frequently involved in attacks on humans, e.g., the most often mentioned are Staffordshire Bull Terrier, ‘pit bull-type’ dogs, Rottweiler, German Shepherd, Doberman, and Labrador Retriever ¹³. Furthermore, dog attacks can be fatal, with an estimated 10–20 deaths occurring annually in high-income countries such as the US ¹⁴. Mortality rates are likely higher in low and middle-income countries ^1,2, but available data for such regions are scarce and fragmented ⁷. Limited capacity and training, poor access to diagnostic tests, poor recognition of rabies, lack of coordination between veterinary and medical authorities, and lack of understanding of bite victims about when and how to treat injuries add to mortality rates.

Although fatalities in recent years are relatively rare, dog bites are commonly associated with physical and physiological trauma ¹⁷ such as permanent disfigurement ¹⁸ or the development of post-traumatic stress disorders ¹⁹. Moreover, they can lead to serious bacterial infections ²⁰ and the transfer of infectious diseases such as rabies or tetanus ²¹. Rabies, a potentially fatal disease caused by a virus of the genus Lyssavirus, is a global disease that currently occurs on all continents except Antarctica ²². The rabies virus is a pressing concern because, when left untreated in humans, it has one of the highest fatality rates in the world ²³. Nearly all terrestrial mammals, including humans, can be affected by rabies ²⁴. Despite long-term efforts to eliminate the virus, it remains present in both wild and domestic animal populations.

Domestic dogs account for almost 99% of human rabies cases ⁷. Each year, nearly 60000 people die around the world from dog-transmitted rabies, with the highest incidence rates occurring in Africa and Asia ²³. Transmission to humans is commonly caused by bites or scratches by infected animals, however, not every bite by a rabid dog will result in rabies. Rabies transmission depends on several factors, including the location of the body where the person is bitten and the subsequent progression of the virus to the central nervous system. Once the virus spreads from the nervous system to other parts of the body, mainly the salivary glands, there is essentially no remedy ^6,23. Post-exposure prophylaxis (PEP), i.e., post-exposure vaccination, is the most effective preventive treatment of rabies for humans exposed to transmission. Around 29 million people each year are vaccinated following an animal bite, and every hour, more than 3000 people are involved in life-threatening emergencies resulting from dog attacks in rabies-endemic countries ⁷.

Although the number of rabid dogs has decreased extensively due to vaccination efforts ²⁵, sporadic cases are still recorded through transmission cycles via wildlife ²⁶. Most western European countries are currently considered rabies free ^25,27; however, rabies is a cross-border disease that has no geographical barriers, and there is still a risk of reoccurrence in the countries where it was claimed to be eliminated ^26,28. Furthermore, the almost complete elimination of human rabies in industrialised countries could create a false sense of security that rabies no longer poses a threat to the public ²⁸. Data on animal bite injuries are important to predict the potential number of transmissions. Information on the incidences in what circumstances people were bitten, whether by a suspected dog and at what sites of the body, is vital to estimate the probability of receiving PEP ²⁹. Human populations, and the populations of their domestic dog companions, are forecasted to increase, and, along with it, the incidents of dog bites and canine-induced rabies. Thus, it is crucial to understand the circumstances surrounding dog attacks and dog bites in order to develop effective preventive methods to reduce the number of incidents ³⁰.

Mandatory vaccinations for all domestic dogs were introduced in Poland in 1950, and the number of rabid dogs subsequently decreased during the 20th and 21st centuries. Oral rabies vaccine (ORV) was introduced for the first time in 1993 in the western part of Poland, and since 2002, it was implemented nationwide. This facilitated the almost complete elimination of the virus in the wild in Poland ²⁷. However, cases of rabid domestic animals are still being reported, most often due to owners not following dog vaccination requirements ³¹. Furthermore, rabies is still prevalent within the eastern border countries of Poland, such as Russia and Ukraine, and the spill over transmission from wildlife to Poland is highly probable. Post-exposure vaccines are applied to approximately 7000 people in Poland each year ³².

Thus, the main goal of the study was to examine the dog bite incidents to humans and the potential risk of rabies in Poland. Broad studies describing dog bites have been published in the last two decades, for example, in the UK ^33,34, Finland ³⁵, Canada ³⁶, USA and Jamaica ³⁷ and in Morocco ³⁸. However, to our knowledge, no comprehensive details related to human-dog incidents in Poland are available. We, therefore, specifically aimed to: a) assess temporal and spatial trends in human exposure to dog bites, b) describe demographic differences in dog-related human-injuries, c) identify circumstances associated with dog bites and description of injuries and, d) identify dog breeds involved in bite incidents with specific focus on aggressive breeds.

Temporal and spatial trends in human exposure to dog bites. Between 1999 and 2014, a total of 79964 people (annual mean ±SD: 4980.3 ±423.9) were vaccinated against rabies after being exposed to suspected rabid dogs, both wild and domestic (Table S1). A total of 55260 of those cases (annual mean ±SD: 3947.1 ±398.8) were considered as ‘deep human injuries’ (category III exposure) ³². The mean density of people (number of people per 100 km²) along with the mean density of people vaccinated against rabies due to contact with potentially rabid dogs in each voivodeship between 1999 and 2014 (Fig. 1) shows that the lowest number of vaccinated people was located in in the western and eastern voivodeships, and the highest number in the south-eastern, southern and central voivodeships (Fig. 1b).

Vaccinations due to dog bites were almost always greater in urban (n=46459) compared to rural (33505 cases) areas (χ2 (1, n = 79964) = 2098.52, p < 0.01) (Fig. 2; Table S1). The exceptions occurred in 2000 and 2001, when vaccinations in rural areas were higher than in urban areas (Fig. 2). The reported number of rabid dogs was highest in 2001 (n=104), which gradually decreased to only 9 reported rabid dogs in 2014 (Table S1).

Demographic differences in dog-related human-injuries and vaccination. Men were bitten and subsequently vaccinated more often (annual mean ±SD: 2707.42 ±251.19) than women (2290.33 ±273.93; Table S2). The national mean (±SD) annual incidence of people vaccinated due to dog bites between 1999 and 2014 was 13 (±1.09) people (Table S3). The number and proportion of dog bite-related vaccinations, with respect to sex and age group of the victim, was reported per 100000 inhabitants (Table S4). For males, the greatest mean number of vaccinations was with the age group between 7-17 years (23 ± 3.52), followed by men between 0-6 years (16 ± 4.60), and finally men >18 years (11 ± 1.07). The pattern was similar for females. The highest mean number of vaccinations occurred with females between 7-17 years (19 ± 2.75), followed by females 0-6 years (13 ± 2.84), and finally females >18 years (9 ± 1.56). Within all age groups, men (15 ±1.33) had a higher average incidence of vaccinations than women (12 ±1.37) (Table S3). Thus, the age group most at risk to rabies transmission and subsequent vaccination was people between 7-17 years old (OR=0.86), followed by children 0-6 years (OR=0.44), with the older group of children being the least exposed (OR=0.29; Table 1). Males (OR=1.28) also had a higher risk factor than females (OR=0.78).

Circumstances associated with dog bites and description of injuries. The most common circumstance surrounding dog bite incidents was when ‘the dog was unknown to the bitten person’, which occurred in 17.43% (n=156) of all cases. Other common circumstances included when ‘a dog was chained but escaped’ at 10.95% of all cases (n=98), followed by ‘an attack that occurred within dog’s territory’ at 8.83% (n=79), and ‘an attack in proximity to the dog owner’s property’ at 7.82% (n=70). There was only one reported case of an attack by a dog that was taken from an animal shelter, and a few incidences when the dog was under a child’s supervision (n=8). Most of the biting incidents included dogs that were not owned, that is, they were free-ranging or stray, while owned animals were involved in only 5.03% (n=45) of the cases. Of these, a total of 6.15% (n=55) of the incidents involved dogs that were known to, but not owned by, the victim. In the rest of the incidents, the dog was either not supervised (7.60%; n=68), the person was bitten randomly on the street (6.93%; n=62) or the person approached the dog (6.48%; n=58). All other information regarding the circumstances surrounding dog bite incidents (n=895) between 2000 and 2018 are summarised in Table S4.

The most common biting incidents among children (both genders) were with a dog that was unknown to the victim, and when the dog was not supervised (Fig. S1). The incidence of such bites among children aged 7-17 years was relatively lower. The most frequent reasons surrounding the incidents included the accidental escape of the dog, an attack near dog owner’s property, or the incident was caused by an unknown dog. For adults, the attacks took place the most often when the victim approached the dog and were caused by a leashed dog or by a dog that was unknown to the victim (Fig. S1).

A pairwise comparison between children (<18 years) and adults (>18 years) showed a significant difference between the circumstances surrounding dog bites between the age groups (Fig. 3). A high mean difference (MD= 0.93) between children and adults when the victims approached the dog (Table S4), indicating a higher incidence of attacks in children (p < 0.001) compared to adults. Similarly, the significant mean difference was greater for children than for adults when the approach was toward a dog owned (MD = 0.56) and within the dog’s territory (MD= 0.97), with p < 0.001 indicating a higher likelihood of attacks on children under the aforementioned circumstances. A significant low mean difference was observed between children and adults when the attack was within the proximity of dog owner’s property (MD= -0.85) and when the dog ran away despite being chained (MD= -0.71; p < 0.001). These results indicated a higher incidence of dog bites among adults compared to children under the stated circumstances (Table S4).

In general, the reported dog bite injuries (n=309) were mostly in the head and neck area (31%), followed by the lower extremities (21%) and the upper body (18%) (Fig. 4). On average, for children between 0-6 years of age (Fig. 4a), the most frequently attacked body part was the head (41.14%), affecting females more (44.44%) than males (37.84%). This was followed by attacks on the neck (13.66%) and legs (13.66%). No cases of chest, back, and hands injuries were reported in males in this age group (0-6 years). The distribution of injuries for children between 7-17 years (Fig. 4b) shows that attack on the head still remains the most frequent (21.46%) for children in the age group of 7-17 years, with injuries to males being slightly more frequent (22.22%) than to females (20.69%). Injuries in the extremities (both upper and lower) account for 16.16% and 19.73% of attacks on average, respectively, and males are injured more than their female counterparts. However, females sustained more injuries to their face (20.69%) than males (11.11%). No neck injuries were reported for males in this age group (7-17 years). However, for adults (18 years and above), head, face, and neck areas were also the least bitten body parts for both genders (Fig. 4c). However, legs suffered the most injures overall (28.68%), accounting for 31% of bites for males and 26% for females.

Dog breeds involved in bite incidents. Out of the collected reports of dog-bite incidents, 251 reported the dog breed involved. These reports included 24 recognised breeds as well as ‘mongrels’, or the non-pure-breed dogs. Among all breeds, the mongrel was the most frequently involved, at approximately 31.07% (n=78) of the total cases (SI Table 6). Mongrels were followed by the German Shepherd with 22.71% (n=57), American Staffordshire Terrier with 15.54% (n=39), American Pit Bullterrier with 6.37% (n=16), and the Rottweiler with 5.98% (n=15). The word cloud (Fig. 5) shows the dog breeds most involved in bite cases. Dogs belonging to so-called ‘aggressive breeds’ were responsible for 16.33% (n=41) of all dog-biting incidents with identified dog breeds (including mongrels).

Aggressive dog breed occurrences in Poland. Between 2015 and 2018, the most frequent ‘aggressive breeds’ registered by the Polish Kennel Club (PKC) and the Purebred Dog Breeder Association (PDBA) was Rottweiler (mean ±SD: 685.00 ±62.13) and Caucasian Shepherd Dog (443.00 ±17.01) (Table S7). The least registered by PKC and PDBA were the American Bulldog (7.00 ±1.22) and American Pit Bull Terrier (registered only twice in 2018); both dog breeds are not recognised by the FCI. For all aggressive breeds, except the American Pit Bull Terrier, there were fewer dogs registered by communes than with the PKC and PDBA. The American Pit Bull Terrier was registered with the communes but not with PKC and PDBA. There was discrepancy between the number of puppies born and number of individuals registered in communes. The number of puppies was much higher than the number of individuals registered in communes in the same year (Table S7).

To the best of our knowledge, this was the first longitudinal and national evaluation regarding the occurrence of dog bites, and incidence of exposure to rabies PEP in Poland. Our results showed that the mean annual dog bite incidence rate in Poland was 13 people per 100000 inhabitants, with almost 5000 people vaccinated annually post exposure. Children were more likely to be bitten than adults and males more likely than females, with the incidents occurring under different scenarios, and bites occurring on different parts of the body, for different age ranges. People were more likely to be bitten by mongrels than by purebred dogs, with German Shepherds being the most reported breed associated with dog bite incidences.

The mean annual dog bite incidence rate in Poland was similar to results shown for Zambia (12.9 cases per 100000 people³⁹), while the annual incidence rate was much higher in the UK (1873 per 100000 people ³³), India (1740 per 100000 people ⁴⁰) and the US (107.2 per 100000 people) ⁴¹. The incidence rate varies widely across Europe. For example, the annual incidence rate is estimated at 830 per 100000 people in the Netherlands ⁴², 180 per 100000 people in Switzerland ⁴³, and 71.3 per 100000 people in Spain ¹⁰. It is important to note that the real number of dog bite incidents is often highly underestimated ^10,44. For example, Fiszdon & Borutes ¹² suggested that thousands of dog bite incidences occur annually in Poland, but the majority are not reported to hospitals or veterinary centres. This is likely because the reporting system in Poland is not well established ⁴⁵, and many cases that does not cause serious injury are unreported ⁴⁶. Consequently, we expect that the true number of dog bite cases in Poland is likely much higher.

Our results suggested that children were more likely to be bitten by their family dogs, or when they approached other dogs. This corresponds to other research showing that, in most dog bite incidents, the dog is owned by a family member, and children are most commonly bitten in the home ^47,48. Reisner et al., ⁴⁹ reported that 42% of the bite cases occurred in circumstances where the dog was familiar with the child, and the authors attributed these to bites in response to food guarding. We found that biting accidents in adults were more likely to occur for when a chained dog had escaped, or when a dog was near their owner’s property. This is generally consistent with other studies, which reported that 65% or more of the bites occurred within the victim's own home ^50–52, or with an escaped dog ¹⁶.

Similar to other research, our findings suggested that adults of both genders were bitten the least in the head and neck areas (<10%), but sustained more bites in their extremities ¹⁵ including the hands, legs, and feet ^17,53. Adults are generally taller than children, and their lower extremities are the most exposed body parts, regardless of whether they fight the animal off or run away ^15,43. On the other hand, children <6 sustained more head and neck injuries, which is not uncommon 47. This is believed to be the result of a number of factors, including the child’s height and the tendency to crawl or play on the floor ⁴⁸. Furthermore, the ability to correctly interpret dog behaviour improves with age, and children <7 generally struggle to identify fear-related behaviours in dogs ^54,55. Finally, children >7 are more likely to sustain injuries to their lower and upper extremities, presumably due to their increased height and the limbs being the closest point to the animal during an attack ⁴⁸. Our study showed similar results, where ~20% of all injures were sustained in the head and limbs.

In our study, male children were bitten more frequently than female children, which is consistent with other research ^37,56,57. In general, children are 3-5 times more likely to be bitten than adults ^58,59. Consequently, children require hospitalization and undergo surgeries more often ¹¹. Such injuries are associated with high medical costs ⁶⁰ which equal approximately $165 million annually in the US ⁴¹, with mean hospitalization cost reaching $18200 per capita ⁹.

Mongrels and the German Shepherds were the most frequently reported dog breeds involved in the incidents in our study, which is similar to some previous studies ^57,61,62. However, this finding should be interpreted with caution. The accuracy of the dog breed reported by victims may be unreliable, and German Shepherds may simply be easily recognizable ⁶³. Previous studies have reported inaccuracies in identifying dog breeds, especially 'bull' breeds ³⁴. Furthermore, some dog breeds are commonly described as ‘genetically pre-dispositioned to be mean' or having 'killer instinct'. Using such terms leads to demonization of certain breeds of dogs ⁶⁴, negatively influencing the public’s perception of the danger associated with those dogs ⁶⁵ and could lead to higher reporting rates. Environmental factors and personality traits are considered better predictors of biting than the features connected to breeds ¹⁵, which is why the aggressive potential should be evaluated for dogs on an individual basis, rather than by breed ⁴².

In our study, the so called ‘aggressive’ breeds, such as American Pit Bull Terrier or Rottweiler, were also commonly involved in biting circumstances. Furthermore, only 16% of dogs involved in biting incidents were from the list of ‘aggressive breeds’. However, in our opinion, the current classification of certain breeds as ‘aggressive’ seems irrelevant, as there was no justification provided for the chosen breeds. Research shows that such classifications of ‘dangerous’ dog breed are criticised, as in the Netherlands ⁴² and Spain ⁶⁶. Moreover, we found that the aggressive dog breeds owners do not register these dogs in communes as required by the law.

Educational practices play an important role in decreasing the number of dog bites and limit the transfer of misinformation about breed characteristics and human-canine interactions ³. Although bites should be regarded as preventable injuries, mistakes will happen and therefore sufficient knowledge should extend to what a child and caregiver should do during a dog bite incident in order to reduce injury severity, in addition to post-bite action such as psychological support ^47,67,68. Dog training programs are also important to provide owners necessary knowledge about dog behaviour and wellbeing, as well as the instruments necessary to effectively manage possible behavioural problems ⁶⁷ as well as recognition and treatment of the early signs that a dog may bite in the future ⁶⁸.

Finally, as a result of the effective rabies vaccination program in domestic and wild animals in Poland, the number of rabid dogs has significantly decreased. Thanks to an oral immunisation program introduced in 2002, rabies in wild animals has been almost completely eliminated in Poland, and the last, single case of rabies in domestic animals was noted in 2017 ²⁷. The situation varies for neighbouring countries, with the last case in Lithuania, Slovak Republic, and Germany noted in 2013, and Belarus in 2016. However, rabies is still present in domestic animals in Ukraine, where 1449 cases were recorded in 2018, and 368 cases in 2019 ²⁷. It is impossible to predict how the current conflict in Ukraine will affect their rabies mitigation programs. However, for the time being, human rabies was last observed in Ukraine in 2010 and Belarus in 2012 ²⁷.

The large number of people vaccinated for rabies in southern and south-eastern Poland could be associated with the neighbouring Ukraine, where the number of rabies cases is still high compared to the rest of Europe. The Carpathian Mountains could serve as migratory corridor for wild animals between countries, which could facilitate rabies transmission. Additionally, the south eastern regions of Poland have more rural communes where free-ranging dogs are both common and have the potential to come into contact with rabid animals ⁶⁹.

Limitations

Some of the data of our study were based on google searches. However, this was the only source of any data as there was a lack of reports from any official bodies. Moreover, the data on dog bite reporting could be underrepresented as people may be more likely to report being bitten by stray dogs or aggressive breeds, or bites in children, and less likely to report incidents that occur in the home or happen to adults. Furthermore, in our study mongrels were most associated with dog-bite incidences, but that could also be because there are many more mongrels than pure bred dogs in Poland.

Our study adds to the growing body of literature regarding the occurrence of dog bites in humans, and the incidence of exposure to rabies. In the line of the results from other studies worldwide, dog bites were mostly associated with children and young people. In addition, men in general were more frequently bitten by dogs. These reported cases were so severe that they required PEP vaccinations. Two important conclusions can be drawn from our study. Firstly, the so called ‘aggressive’ breeds list does not work in Poland. Secondly, the vast majority of the biting incidents included dogs that were not owned, i.e., they were free ranging or stray, whereas owned animals were involved in only a small proportion of biting cases. This is important because as stray dogs are more difficult to regulate in terms of their vaccination status, people are more likely to come into contact with rabid animals and get the disease and are more likely to bite people. Thus, we recommend that Poland increase its efforts to catch stray dogs to decrease the incidence of dog bites and the potential exposure to rabies. We further recommend official reporting of all cases of dog bites by all associated stakeholders involved in such data collection, for example, hospitals, police and veterinary offices.

Study area. This study was conducted in Poland (312696 km²), located in central Europe (between 49°N to 55°N and 14°E to 25°E). The climate is mostly temperate with warm summers (18°C to 30°C) and relatively mild winters (−6°C to 3°C). The most recent census in 2019 estimated that the Polish population included ~38 million people, with the majority living in urban areas (60%) rather than rural areas (40%) ⁷⁰. Poland is divided into 16 administrative provinces called ‘voivodeships’ which are made up of 2477 local governments called 'communes'. The mean number of people per 100 km² between 1999 and 2014 across all of Poland was 12240 ±48.8 (Fig. 1a).

There are ~6-8 million domestic dogs in Poland ⁶⁹, of which 75000 to 650000 are considered stray animals, i.e., roaming freely without an owner ³¹. Preventive vaccination against rabies is mandatory for all domestic dogs over 3 months old, according to the Act on Animal Health Protection and Combating Infectious Animal Diseases (wetgiv.gov.pl). Due to effective PEP, rabies has not been recorded in the human population in Poland for several years. Rabies-induced human fatality is rare in Poland, with the last death from rabies occurring in 2002 ³².

Data Collection and Data Analyses

Temporal and spatial trends in human exposure to dog bites. There is no regularly published official information on the nature of dog bite incidents in Poland. The only data available on potential rabies transmission include the number of people bitten by wild and domestic animals, including dogs and the number of PEP reported. Rabies vaccines are provided to people involved in exposure categories II (nibbling of uncovered skin, minor scratches or abrasions without bleeding) and III (single or multiple transdermal bites or scratches, contamination of mucous membrane or broken skin with saliva from animal licks, exposures due to direct contact with bats) ³². Furthermore, data on dog-related incidents are limited to before 2014. After 2014, annual reports only include information on whether a person was vaccinated after encountering a potentially rabid animal, either wild or domestic.

We therefore explored trends in the number of dog bites associated with potential rabies transmission, i.e., the number of reported cases of PEP due to dog bites (1994-2014) and tested whether the incidents occurred more often in rural or urban locations using Chi-square tests. National statistics on dog bites and post-exposure vaccination (1999-2014) were collected and concatenated using annual reports published by the National Institute of Hygiene, National Research Centre of Public Health – Department of Epidemiology (NIH-DE), and the Chief Sanitary Inspectorate – Department of Diseases Surveillance and Health Promotion (SI-DDSHP).

We included the following data to show the spatial distribution: i) mean annual human density in Polish voivodeships in years 1999-2014 per 100 km² based on statistical data ⁷⁰; and ii) mean annual people vaccinated against rabies due to contact with potentially rabid dogs. The density of people in Polish voivodeships in periods between 1999-2002, 2004-2007, and 2011-2014 per 100km² was based on data published by National Institute of Hygiene – Department of Epidemiology (NIH-DE). The maps were assembled in MapInfo Software version 11.0. in Transverse Mercator Projection with special Polish parameters (Coordinate System 1992).

Demographic differences in dog-related human-injuries. Information regarding demographic differences in dog bites and subsequent PEP vaccinations (1999-2014) was collected after reviewing reports published by researchers of National Institute of Public Health - National Institute of Hygiene in Warsaw, Department of Epidemiology, and in the Polish journal titled Przegląd Epidiomologiczny [Epidemiological Chronicle]. The data for this time period included detailed information about how many people were vaccinated, the gender of the bitten person (male/female), and their age groups (0-6, 7-17, and > 18 years old (SI Table 2, 3).

Analyses were performed for variables related to the bitten person (age and gender), and the circumstances of the incident (e.g., unsupervised dog or dog under a child’s supervision). In addition, some variables related to the person (gender, age and injury site) were analysed in order to detect possible risk factors in the occurrence of bite incidents. Odds ratio (OR) and 95% confidence intervals (CI) were calculated for gender and age group to determine the most vulnerable group. Variables were positively associated with dog bite incidents when OR > 1 (risk factor), and negatively when OR < 1.

Circumstances associated with dog bites and description of injuries. We used internet search engines (www.google.com) to search for detailed information about dog bite incidents in Poland between 2000 and 2018 using the following keywords in Polish “(dog OR dogs) AND (bite* OR injury OR accident). From this search, we collected materials published in Polish national newspapers (i.e., www.przeglad-tygodnik.pl, wiadomosci.gazeta.pl) and from Police reports published on official websites (i.e., www.policja.pl). In total, we collected 261 relevant independent dog bite cases. We scanned these cases for detailed information surrounding the circumstances of each incident and created a database from the extracted information. The information collected included the year of the incident, demographic information about the people being bitten, e.g., age and gender, and information about the persons’ injury sites.

We also collected information about the dogs involved such as the number of dogs taking part in the incident, whether the dog was adopted from a shelter, the relation of dog to the bitten person (dog owner, not the owner but knew the dog, did not know the dog), and the circumstances of the incident: whether the dog was a) confined (leashed or chained) b) not leashed but supervised by the owner, c) not supervised at all, d) chained in the owner’s property but escaped. We also noted whether the bite incident occurred in the dogs territory, where the incident occurred in relation to dog owner’s property (i.e., on or off their property), if the incident occurred on the street (public property) or the dog entered the property of the person who was bitten, if the dog was under supervision a child or adult, and if the owner/supervisor of the dog was drunk while the incident occurred. We also noted other details of the scenario including if the person approached the dog, the bite occurred while playing with the dog, the bite occurred while separating two fighting dogs, the bite occurred because the dog was encouraged to do so by the owner, or if the dog was using defensive behaviour against an aggressive person.

A heat map was created to show the reported circumstances of dog bites among different age groups (0-6 years; 7-17 years and >18 years) and gender. This was based on the percentage of frequency of reported circumstances of dog bite cases. Furthermore, to understand the differences among circumstances of dog bite incidents and age groups, the age groups were further grouped under two broad categories namely, children (<18 years) and adults (>18 years). A pairwise statistical analyses was conducted using R ⁷¹ with ggplot2 packages ⁷². We tested the significance using post hoc Tukey test comparisons adjusting p-value according to the Benjamini-Hochberg procedure ⁷³.

Dog breeds involved in bite incidents. We noted the type of dog breed involved in the 261 independent dog bite cases we found during our Google search. In Poland, the Polish Kennel Club (PKC) is the main organisation which provides registration number of individual dog breeds recognized by the Fédération Cynologique Internationale (FCI). PKC registers breeding adult dogs as well as puppies and collects information about dog breeds whose breeders are in the process of application for being recognized by the FCI. After 2010 in Poland, several other organisations were established, including the Purebred Dogs Breeder Association (PDBA), which associates dog breeders who are not members of PKC for all dog breeds, including those recognized by the FCI as well as other kennel clubs. Data on dog breeds from PKC and PDBA were available for the periods of 2009-2018 and 2011-2018, respectively.

Aggressive dog breed occurrence in Poland. Breed-specific legislation relating to dangerous or so called ‘aggressive’ dog breeds applies in Poland, with a list of eleven breeds under the regulation of Ministry of Interior and Administration, as implemented in 2003 (Dz. U. of 2003 No 77 item 687). The list includes American Pit Bull Terrier, Majorca Mastiff, American Bulldog, Dogo Argentino, Presa Canario, Tosa, Rottweiler, Akbash Dog, Kangal Shepherd Dog, Moscow Watchdog, and Caucasian Shepherd dog breeds. The Animal Protection Act (Dz. U. of 1997 with later corrections of 2003 No106, item 1002) states that owning a dog from the above list requires the registration of the dog and its owner in the commune, with subsequent permissions granted. However, only pure dog breeds with the issued pedigree certificates can be registered. We discovered that Majorca Mastiff, Dogo Argentino, Kangal Shepherd Dog, Presa Canario, Tosa, Rottweiler, and Caucasian Shepherds are breeds officially registered by the FCI, whereas four breeds, i.e., the American Bulldog, Akbash Dog, Moscow Watchdog, and American Pit Bull Terrier, are not recognized by this organisation. However, these four breeds are recognized by dog associations or clubs in the countries from which they originated. We collected data on the number of registered adult and new-born puppies of all aggressive dog breeds in Poland, except Akbash which was not recognized as a breed with any organization during that time in Poland. A word cloud was created to show the breeds most involved in dog bite incidents, including aggressive breeds.

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Acknowledgements

We thank Agnieszka Hadała for reviewing relevant literature associated with the research. We additionally thank the Polish Kennel Club and Purebred Dogs Breeder Association along with respective municipalities in Poland for providing data on dog breeds.

Author contributions

I.A.W conceived the idea; I.A.W and M.H collected the data; S.M.B processed and analysed the data; M.H analysed spatial data; I.A.W., S.M.B, M.H and A.G.T led the writing of the manuscript. All authors contributed critically to the drafts and gave final approval for publication.

Funding

S.M.B is supported by the project ATUT PhD Programme in Biology. The project is co-financed by the European Union under the European Social Fund – Operational Programme Knowledge Education Development Axis III Higher Education for Economy and Development, Action 3.2 PhD Programme.

Competing interests

The authors declare no competing interests.

Data availability

The datasets generated during and analysed during the current study are available from the corresponding author on request.

Table 1. Results of the risk factor analysis according to sex and age of victims per 100000 people.

Factor	Group	n	OR	CI
Sex	Male	16.12	1.28	1.31-1.07
	Female	12.68	0.78	0.77- 0.87
Age	0-6	13.73	0.44	0.10-0.02
	7-17	20.36	0.86	0.40-0.09
	≥18	9.94	0.29	4.78-1.03

n = number of victims per 100,000 in each group; OR = odds ratio, CI = confidence interval

No competing interests reported.

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Prevalence and circumstances of dog bites in Poland – a longitudinal study

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