Introduction

It has been estimated that there are over 72 million dogs, 81 million cats, and 11 million birds living in households in the United States. 1 In addition, there are many less traditional pets described that encompass a variety of smaller mammals, such as rabbits and various rodents, fi sh, and reptiles. Unfortunately, along with the many benefi ts of pet ownership, there are potential risks, including that of sustaining a bite.

In 2001, over 360,000 people were treated in a U.S. emergency room for a dog bite - related injury with just over 42% occurring in children under the age of 15. 4 It has been estimated that dog and cat bites are responsible for around 1% of ER visits annually. A study reviewing 1994 data estimated that almost 4.5 million animal bites occurred annu-ally; with just over 750,000 of the bite recipients seeking medical attention, either in an ER or other medical facility. 5 Sixty percent of bites are from dogs and an estimated 10 – 20% are from cats. 2

Animal bites can result in trauma that can range from superfi cial lacerations, to deeper tears, frac-tured bones, and crush injuries. Some bites can pen-etrate into joint spaces or body cavities. In addition to the damage to tissue, there is also a risk of infection.

6 Pet Bites

Martha B. Fulford

311

Dog b ites

While any dog might potentially bite a human, the breeds that are the most commonly reported are pit bull terriers, rottweilers, and German shep-herds. 5,6 The relative risk from individual breeds is an area of considerable debate, as is whether any breed - associated risk arises from genetics (nature) or training (nurture). While some studies identify high - risk breeds, either for absolute number of bites, the relative percentage of bites, or the likeli-hood to cause severe injury, it is important to rec-ognize that dogs of any breed can bite, and bites of dogs of any size can cause serious injury or infec-tion. Bites from larger dogs are more likely to result in severe crush injury and penetrate body cavities or joint spaces. Young children are more likely to be bitten in the head or upper body area, while adults are most likely to be bitten on the hand. 2 The majority of dog bites are from dogs known to the victim, with 80% of the dog bites incurred by chil-dren and adolescents caused by a family or neigh-borhood dog. 3

Cat b ites

In contrast to dog bites, victims of cat bites are more often adults and more likely to be women. Bites are most often in the arms or face and usually

Companion Animal Zoonoses Edited by J. S. Weese and M. B. Fulford© 2011 Blackwell Publishing Ltd. ISBN: 978-0-813-81964-8

312 Companion Animal Zoonoses

signifi cance, is Capnocytophaga canimorsus that can cause fulminant infection in immunocompromised hosts following a dog bite or lick. Table 6.1 sum-marizes some of the more common pathogens found in different animal bite infections.

Assessment and m anagement

Initial management of a bite injury involves a careful history, examination of the bite and associ-ated structures and assessment for the risk of infec-tion. The history should include the type of animal, whether it was a provoked or an unprovoked bite,

provoked (although the person may not recognize they are provoking the cat). Though there are less data regarding breeds of cats with a propensity to bite, one study from Spain found that Siamese cats infl icted 43% of reported cat bites. In most areas, domestic short - haired cats are the predominant “ breed, ” and little information about breed - specifi c risk is available.

As with dogs, the majority of bites, 68%, were from cats known to the victim. 7 The long, very narrow teeth of a cat can cause deep penetrating wounds that are more prone to infection. If the bite is near a bone or joint, there is a higher risk of a septic arthritis or tenosynovitis as a result of punc-ture into the periosteum or joint space. Cat scrat-ches are a particular risk for the transmission of Bartonella henselae .

Rodent b ites

The incidence of bites caused by pet rodents is unknown, but anecdotally, it appears to be rela-tively high. Rodents, by virtue of their generally small size, are unlikely to cause signifi cant trauma when they bite. However, these bites need to be considered as there are certain specifi c infections associated with rodents. Rat bites may result in rat - bite fever, caused by either Streptobacillus monil-iformis or Spirillum minus . Lymphocytic chorio-meningitis virus, a virus found in several rodent species, has been associated with hamster bites. Secondary infections from various opportunistic bacteria from the rodent ’ s oral cavity or the per-son ’ s skin can also develop.

Microbiology

Bite infections are usually polymicrobial caused by a mix of aerobic and anaerobic organisms 8 that originate from the mouth of the biting animal and from the skin of the victim. Some of the more common aerobes found include streptococci, staphylococci (including methicillin - resistant Staphylococcus aureus [MRSA]), Moraxella , and Neisseria . Common anaerobes include Bacteroides , Fusobacterium , and Prevotella . Pasteurella was the most common pathogen from both dog and cat bites, with a predominance of Pasteurella canis from dogs and Pasteurella multocida subspecies multocida and septica from cats. 8 Less common, but of clinical

Table 6.1 Oral m icrofl ora that c an b e a ssociated with b ite i nfections. 8 – 10

Animal Oral fl ora

Dog Pasteurella spp. including P. canis , Staphylococcus aureus (including MRSA), Staphylococcus pseudintermedius , Streptococcus spp., Moraxella spp., Neisseria spp., Capnocytophaga canimorsus , Fusobacterium spp., Bacteroides spp., Porphyromonas spp., Prevotella spp., Clostridium spp.

Cat Pasteurella multocida , other Pasteurella spp., Streptococcus spp., Staphylococcus spp., Moraxella spp., Fusobacterium spp., Bacteroides spp., Porphyromonas spp.

Rat Mixed aerobes and anaerobes, including Streptobacillus moniliformis and Spirillum minus

Primates/human

Streptococcus spp. (including Streptococcus pyogenes ), Enterobacteriaceae, Eikenella corrodens , Neisseria spp., Enterococcus , Staphylococcus spp., anaerobic gram - negative bacilli including Fusobacterium spp., B virus (Cercopithecine herpesvirus 1) (monkeys only)

Fish/marine animals

Organisms found in marine environment, including Vibrio and Aeromonas spp.

Reptiles Mixed aerobes and anaerobes, including Salmonella spp.

Pet Bites 313

any unusual behavior on the part of the animal (to help determine rabies risk), and vaccination history of the animal (if available). The animal should be identifi ed and the owner should be contacted if possible, so that information regarding the ani-mal ’ s health status and rabies vaccination can be obtained. The pertinent history taken from the victim should include medical history with a focus on any risk factors for immune suppression (e.g., splenectomy, diabetes), medications and allergies, and tetanus immunization status.

The initial assessment of the bite involves careful assessment of the wound and the type of damage (e.g., crush injury, laceration, puncture) and involvement of any underlying structures. The time of the bite with respect to the time of presenta-tion should be noted. Careful examination for any damage to nerves or vessels must be done. Both the wound and surrounding tissue need to be inspected for any signs of local infection and note should be made of any signs of systemic infection such as fever or lymphadenopathy.

Depending on the location and depth of the injury, there may be a need for specifi c diagnostic tests. If there is suspected bone or joint involve-ment, radiographs should be taken to assess for joint disruption or bone fractures. A radiograph might also be helpful to rule out any foreign bodies. Bites that are infected should be imaged to assess for the degree of tissue injury, for any evidence of subcutaneous gas as well as looking for bony injury. Certain bites to the head, especially a dog bite to the head of an infant or small child, may result in a skull fracture or cause a penetrating injury with subsequent brain abscess formation. Such injuries should be evaluated with a CT scan or MRI of the head. There is little value in culturing an uninfected bite. However, if there are signs of infection, tissue should be sent for both aerobic and anaerobic culture. 9 – 13

As bites may be deceptively deep, especially bites from felines, or have signifi cant tissue injury, local anesthesia of the area should be considered to permit more thorough exploration and cleans-ing. The wound should be scrupulously cleaned and irrigated with water or normal saline. 14 For larger bites, the use of a syringe or IV catheter can be used for deeper irrigation. Any devitalized tissue should be debrided, and any dirt or foreign material should be removed (e.g., teeth, fabric from clothing). 9 – 13

Following irrigation and debridement, wound closure can be considered. Bites to the face are usually closed for cosmetic reasons. These wounds have a lower risk of infection, possibly due to an excellent vascular supply and lack of dependent edema. 2,10,13 Plastic surgery assessment should be obtained for any signifi cant facial injury. If less than 12 hours old, a superfi cial laceration from a dog bite that is not on a hand or foot can also be considered for primary closure. 13 Other bite inju-ries are best left open and allowed to close by sec-ondary intention. They should be examined daily for any signs of infection. 9 – 13

All patients presenting with bites should be assessed for the need for tetanus toxoid immuniza-tion and for rabies postexposure prophylaxis.

Bites should be reported to the appropriate public health authorities. This is important to ensure that proper actions are taken with respect to potential rabies exposure, as well as document-ing the bite to identify animals or owners that are recurrent offenders.

Antimicrobials

Antimicrobials used to treat an infected bite wound need to be broad spectrum with good aerobic and anaerobic activity. For dog and cat bites, the anti-microbial or antimicrobial combination needs to have excellent activity against Pasteurella spp. See Table 6.2 for recommended treatment regimens.

Table 6.2 Antimicrobial o ptions for the t reatment of a nimal b ites. 9 – 13

Antibiotic Alternative regimen

Oral Amoxicillin/clavulanic

acid Fluoroquinolone or doxycycline or trimethoprim/sulfamethoxazole plus metronidazole or clindamycin

Intravenous Ampicillin – sulbactam Carbapenem (imipenem –

cilastatin, meropenem, ertapenem)

Piperacillin – tazobactam

Ticarcillin – clavulanate Third - generation

cephalosporin plus metronidazole

Fluoroquinolone plus metronidazole

314 Companion Animal Zoonoses

Table 6.3 General r ecommendations for r educing the r isk of b ites.

Select pet/breed suitable for your lifestyle and home environment (may require consultation with veterinarian, animal behaviorist, etc.).

Exclude animals with a history of aggression — either in that specifi c animal or in the breed.

If possible, spend time with the animal before buying or adopting it.

Spay/neuter dogs.

For dogs, socialize and train them appropriately. Teach them submissive behaviors (e.g., exposing abdomen, giving up food without growling).

Do not play aggressive games with animals.

Delay acquiring dog or other pet if a child is fearful or apprehensive.

Be careful bringing an animal, especially a young animal, into a household with an infant or very young child.

Never leave an infant or young child unattended with an animal.

Teach children basic rules for interactions with dogs/other animals: Do not approach an unknown animal. Never run from the animal or scream at the animal. Remain very still if approached by unknown dog/animal. Avoid direct eye contact with an animal like a dog. Do not disturb an eating or sleeping animal. Do not disturb an animal that is looking after its young. Do not pet a dog or other animal without letting it see you fi rst. If bitten or scratched, immediately tell an adult.

Adapted from Centers for Disease Control and Prevention. 3

There is no consensus on the use of antimicrobial prophylaxis following a bite to prevent infection. Current recommendations are for the use of pro-phylactic antibiotics for certain high - risk injuries: wounds that are primarily closed (e.g., on the face), deep punctures (especially those from cat bites), injuries requiring surgical repair (e.g., certain crush injuries, avulsion injuries), wounds on the hands, and wounds in the immunocompromised. 12,13 The choice of antibiotic would be similar to those used for treatment. Any antibiotic regimen selected must have good aerobic and anaerobic activity and, in the case of cat and dog bites, excellent activ-ity against Pasteurella spp.

Bite p revention

Ideally, no companion animal would ever bite. Unfortunately, bites do occur, but there are mea-sures that can be used to minimize the risk. Examples of these are listed in Table 6.3 . Most of the recommendations are specifi cally aimed at pre-

venting dog bites, but the strategies can be applied to any animal.

References

1. American Veterinary Medical Association . U.S. Pet Ownership and Demographics Sourcebook . 2007 . www.avma.org/reference/marketstats/ownership.asp . Accessed May 14, 2010.

2. Oehler RL , Velez AP , Mizrachi M , et al. Bite - related and septic syndromes caused by cats and dogs . Lancet Infect Dis 2009 ; 9 : 439 – 447 .

3. Centers for Disease Control and Prevention . Nonfatal dog bite - related injuries treated in hospital emer-gency departments — United States, 2001 . MMWR Morb Mortal Wkly Rep 2003 ; 52 ( 26 ): 605 – 610 .

4. Sacks JJ , Kresnow M , Houston B . Dog bites: how big a problem? Inj Prev 1996 ; 2 : 52 – 54 .

5. Shuler CM , DeBess EE , Lapidus JA , et al. Canine and human factors related to dog bite injuries . J Am Vet Med Assoc 2008 ; 232 : 542 – 546 .

6. Sacks JJ , Sinclair L , Gilchrist J , et al. Breeds of dogs involved in fatal human attacks in the United States

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between 1979 and 1998 . J Am Vet Med Assoc 2000 ; 217 : 836 – 840 .

7. Palacio J , Leon - Artozqui M , Pastor - Villalba E , et al. Incidence of and risk factors for cat bites: a fi rst step in prevention and treatment of feline aggression . J Feline Med Surg 2007 ; 9 : 188 – 195 .

8. Talan DA , Citron DM , Abrahamian FM , et al. Bacteriologic analysis of infected dog and cat bites . N Engl J Med 1999 ; 340 ( 2 ): 85 – 92 .

9. Brook I . Microbiology and management of human and animal bite wound infections . Prim Care 2003 ; 30 : 25 – 39 .

10. Dendle C , Looke D . Management of mammalian bites . Aust Fam Physician 2009 ; 38 ( 11 ): 868 – 874 .

11. Brinker D , Hancox JD , Bernardon SO . Assessment and initial treatment of lacerations, mammalian bites, and insect stings . AACN Clin Issues 2003 ; 14 ( 4 ): 401 – 410 .

12. Fleisher GR . The management of bite wounds . N Engl J Med 1999 ; 340 ( 2 ): 138 – 140 .

13. Endom EE . Initial management of animal and human bites . 2010 . www.uptodate.com . Accessed May 13, 2010.

14. Moscati RM , Mayrose J , Reardon RF , et al. A multi-center comparison of tap water versus sterile water for wound irrigation . Acad Emerg Med 2007 ; 14 ( 5 ): 404 – 409 .