The precise number of bite wounds in the United States and worldwide is difficult to determine because many animal bites are never reported. In 2016, there were approximately 60 million pet dogs and 47 million pet cats in the United States.[1] Reports estimate 4.5 million dog bites per year and approximately 800,000 receive medical attention.[2] In 2008, this resulted in approximately 316,000 emergency department (ED) visits.[3] Substantially more dog bites occur than cat bites. These two species account for the majority of (nonhuman) mammalian bite wounds encountered in the ED.
Dog bites typically cause a crushing-type wound because of their rounded teeth and strong jaws. An adult dog can exert 200 pounds per square inch (psi) of pressure, with some large dogs able to exert 450 psi.[4] Such extreme pressure may damage deeper structures such as bones, vessels, tendons, muscle, and nerves.
A bite from a dog is shown below.
View Image | Animal bites. Wounds to the left arm and hip inflicted during a dog attack. |
The sharp pointed teeth of cats usually cause puncture wounds and lacerations that may inoculate bacteria into deep tissues. Infections caused by cat bites generally develop faster than those of dogs.[5, 6]
Limited literature is available on other mammalian bites. Domesticated ferrets are responsible for several documented cases of unprovoked attacks on young children and infants. The bites of foxes, raccoons, skunks, bats, dogs, and cats have been clearly linked to rabies exposure. Bites from monkeys, particularly macaques, are of concern because of the possibility of transmission of B virus, a herpes virus that causes fatal infection in humans.[7] Bites from large herbivores generally have a significant crush element because of the force involved.
Bites of the hand generally have a high risk for infection because of the relatively poor blood supply of many structures in the hand and anatomic considerations that make adequate cleansing of the wound difficult. In general, the better the vascular supply and the easier the wound is to clean (ie, laceration vs puncture), the lower the risk of infection.
A major concern in all bite wounds is subsequent infection caused by bacteria, and, more rarely, viruses. With regard to dog bites, at least 64 species of bacteria are found in the canine mouth, and many resulting infections are polymicrobial.[8, 9, 10]
Common bacteria involved in dog bite wound infections include the following:
Common bacteria involved in cat bite wound infections include the following:
Common bacteria involved in herbivore bite wound infections include the following:
Common bacteria involved in swine bite wound infections include the following:
Common bacteria involved in rodent bite wound infections (rat-bite fever) include the following:
Common bacteria involved in primate bite wound infections include the following:
Common bacteria involved in large reptile (crocodiles, alligators) bite wound infections include the following:
Bite wounds from cats and dogs can occur without provocation, but provoked bites, such as disturbing animals while they are eating, are more common. Older animals often are less tolerant of disturbances, especially by children. Most dog bites involve a dog that belongs to the family or friend of the victim and approximately half occur on the pet owner's property.[11]
Unprovoked bites by wild or sick-appearing animals (most notably by dogs, cats, raccoons, foxes, skunks, and bats) further raise underlying concerns about likelihood of rabies exposure.
United States
Of an estimated 3-6 million animal bites per year in the United States,[12] approximately 80-90% are from dogs, 5-15% are from cats, and 2-5% are from rodents, with the balance from other small animals (eg, rabbits, ferrets), farm animals, monkeys, reptiles, and others.
Out of the 4.5 million estimated dog bites that occur each year, nearly 1 out of every 5 requires medical attention.[2] Reports estimate that in 2008, of the 316,000 ED visits, 2.5% required hospital admission. This number has been on this rise since 1993. There is also increased frequency in rural areas and in the Midwest and Northeast regions.[3]
International
The lack of standard reporting in many countries makes accurate estimates of mammalian bite incidence difficult to determine. Depending on locale, the range of animals inflicting bites is wide and includes large cats (tigers, lions, leopards), wild dogs, hyenas, wolves (Eurasia), crocodiles, and other reptiles. As in the United States, most bites, however, are from domestic dogs. In developing countries, mammalian bites (especially bites by dogs, cats, foxes, skunks, and raccoons) carry a high risk of rabies infection.
Women are more frequently bitten by cats, whereas men are more often bitten by dogs (despite being "man's best friend").[13] For dog bites specifically, men comprise a higher percentage of those presenting to the emergency department (110.4 versus 97.8 visits/100,000), but the sexes are nearly equal for those admitted to the hospital.[3]
The average age of an individual presenting with a dog bite is approximately 30 years, and 75% of all animal bite patients are less than 45 years of age.[3] The peak incidence of animal bites, specifically dog bites, occurs among children aged 5-9 years.[14, 12, 11] Hospital admission rates are higher at the extremes of age.[3]
The prognosis of patients with animal bite wounds is generally excellent.
Dog-bite related deaths range from 20-35 in the United States each year[12, 11, 15] with a 0.5% dog-bite related in-hospital mortality rate.[3] Factors contributing to these fatalities have been reviewed and most commonly include the following[16] :
While local infection and cellulitis are the leading causes of morbidity, sepsis is a potential complication of bite wounds, particularly C canimorsus (DF-2) sepsis in immunocompromised individuals. Pasteurella multocida infection (the most common infection contracted from cat bites) also may be complicated by sepsis. Meningitis, osteomyelitis, tenosynovitis, abscesses, pneumonia, endocarditis, and septic arthritis are additional concerns in bite wounds. When rabies occurs, it is almost uniformly fatal (see Rabies).
Educating patients about the risk of infection despite proper wound care, antibiotics (if indicated), and close follow-up care is very important. Even bite wounds that have received the best care may become infected. Teach patients the signs of infection and the need for prompt attention if the wound should become infected.
For patient education resources, see the Bites and Stings Center and Bacterial and Viral Infections Center, as well as Animal Bites and Rabies.
The history in patients with animal bites should include the following:
Major resuscitation rarely is required. With children, reassurance and parental presence may facilitate examination. Where applicable, consider the following:
Significant damage due to bites is shown in the images below.
View Image | Animal bites. The devastating damage sustained by a preadolescent male during a dog attack. Almost lost in this photograph is the soft tissue damage t.... |
View Image | Animal bites. Massive soft tissue damage of the right leg caused by a dog attack. This patient was transferred to a level one pediatric trauma center .... |
Complications of bite wounds may include the following:
Fresh bite wounds without signs of infection do not need to be cultured. Infected bite wounds should be cultured to help guide future antibiotic therapy.
Other laboratory tests are indicated as the patient's condition dictates (eg, complete blood cell count and blood cultures for patients with sepsis).
If Capnocytophaga canimorsus sepsis is suspected, examine the peripheral smear for the organism, a bacillus.
Radiography is indicated if any concerns exist that deep structures are at risk (eg, hand wounds; deep punctures; crushing bites, especially over joints). Occult fractures or osteomyelitis may be discovered. Radiographs may find foreign bodies in the wound (eg, teeth).
Children who have been bitten in the head should be examined for bony penetration with plain films or a computed tomography (CT) scan. If the child was shaken, consider cervical spine evaluation.
Obtaining the history of the bite event is of major importance, including home treatment of wounds, body parts involved, and other symptoms (see History).
Rinse bite wounds, if possible, and cover with a sterile dressing. Tap water has been shown to be as effective for irrigation as sterile saline.[17]
Encourage patients to seek prompt care.
Most bite wounds can be treated in the ED. Essentials of treatment are inspection, debridement, irrigation, and closure, if indicated. Complete trauma evaluation occasionally is indicated.
Carefully inspect bite wounds to identify deep injury and devitalized tissue. Obtaining an adequate inspection of a bite wound that has not been anesthetized is nearly impossible. Care should be taken to visualize the bottom of the wound and, if applicable, to examine the wound through a range of motion.
Debridement is an effective means of preventing infection. Removing devitalized tissue, particulate matter, and clots prevents these from becoming a source of infection, much like any foreign body. Clean, surgical wound edges result in smaller scars and promote faster healing.
Irrigation is a key means of infection prevention. A 19-gauge blunt needle and a 35-mL syringe provide adequate pressure (7 psi) and volume to clean most bite wounds. In general, 100-200 mL of irrigation solution per inch of wound is required.[17] Heavily contaminated bite wounds require more irrigation. Large dirty wounds may require irrigation in the operating room. If available, povidone-iodine solution has been shown to be virucidal and is recommended for irrigation by the US Centers for Disease Control (CDC) if there is concern for rabies. A 10% solution can be diluted (10 or 20:1) and used to both cleanse the surface of the wound as well to irrigate.[18] Additionally, isotonic sodium chloride solution or tap water are safe, widely available, effective, and inexpensive irrigating solutions. Few of the numerous other solutions and mixtures of saline and antibiotics have any advantages over tap water or saline.[17] If a shieldlike device is used, take care to prevent the irrigating solution from returning to the wound, which may decrease the effectiveness of the irrigation.
It may be difficult to appropriately irrigate small puncture wounds, especially those inflicted by the teeth of a cat. Given that these have a higher rate of infection, consideration should be given to opening the wound with a No. 15 scalpel and creating a 1- to 1.5-cm incision that can be well irrigated and left open to heal by secondary intention.[19]
Studies estimate the rate of infection of mammalian (dog, cat, human) bites to be approximately 6-8% when closed primarily.[20, 21, 22] A study of dog bites showed improved cosmetic scores and no increased risk of infection with primary closure of wounds in multiple anatomic locations with provision of prophylactic antibiotics.[20]
Facial wounds have a low risk of infection even when closed primarily due to their increased blood supply.[10, 23, 20] A randomized clinical trial showed no increased risk of infection (without the use of prophylactic antibiotics) and improved wound healing times with primary closure of facial wounds from dog bites.[23] Given the cosmetic implications of facial wounds, primary closure is therefore advisable.
Primary closure should only be considered in bite wounds that can be cleansed effectively. Bite wounds to the hands and lower extremities, with a delay in presentation (>8-12 hours old), or in immunocompromised hosts, generally should be left open or treated by delayed primary closure.[10] Closure management decisions should be at the discretion of the provider after discussion with the patient and consultation with specialists if available. Deep sutures should be avoided because they can act as a nidus for infection.
If a bite wound involves the hand, consider immobilizing the hand in a bulky dressing or splint to limit use and promote elevation.
Consider tetanus and rabies prophylaxis for all wounds. Antirabies treatment may be indicated for bites by dogs and cats whose rabies status can not be obtained, or in foxes, bats, raccoons, or skunks in the Americas (see Rabies and Tetanus for treatment and dosing information).
Oehler and colleagues proposed the following wound management strategy following animal bites, aimed at preventing severe complications[24] :
For additional information, see Medscape's Wound Management Resource Center.
Patients with infected animal bites may need inpatient care. This depends on the general health of the patient, the extent and nature of the infection, and the patient's likely degree of compliance.
Consider admitting patients with hand bites that become infected (generally those involving deep structures). Consider consultation with the hand surgery service if deep infection, such as involving the tendon sheath or other structures, is suspected, as surgical irrigation may be indicated.
Patients who require extensive repair or prolonged inpatient care may need transfer to a tertiary care facility.
Extensive wounds, those involving tissue loss, or those involving complex structures may require plastic surgery consultation.
If the skull is penetrated, neurosurgery consultation is indicated.
Local public health authorities should be notified of all bites and may help with recommendations for rabies prophylaxis.
Pediatric bite victims are at continued risk of injury unless steps are taken to protect them from future bites. Animal control should be notified for all bites, and child protection services should be contacted for pediatric injuries. To prevent further incidents, the animal should be removed or taken to another location.
Close follow-up care is essential in animal bite wounds. Reevaluate a low-risk bite for signs of infection within 48 hours and a high-risk bite within 24 hours.
In some centers that have an observation unit, admission to that area for direct clinical observation and repeat doses of parenteral antibiotics can be considered on a case-by-case basis.
Use of prophylactic antibiotics is one of most controversial subjects in wound care. Proper wound care (inspection, debridement, irrigation, closure if indicated) reduces infection more than antibiotics. In general, low-risk wounds do not require prophylactic antibiotics. However, therapy is recommended for high-risk wounds (eg, cat bites that are a true puncture, bites to the hand, massive crush injury, late presentation, poor general health).[26]
According to 2014 dog and cat bite treatment guidelines from the Infectious Diseases Society of America, preemptive early antimicrobial therapy for 3-5 days is recommended for the following patients[27] :
The goal of initial therapy is to cover staphylococci, streptococci, anaerobes, and Pasteurella species. Prophylactic antibiotics may be given for a 3- to 5-day course. If the wound is infected on presentation, a course of 10 days or longer is recommended.
The first-line oral therapy is amoxicillin-clavulanate. For higher-risk infections, a first dose of antibiotic may be given intravenously (ie, ampicillin-sulbactam, ticarcillin-clavulanate, piperacillin-tazobactam, or a carbapenem). Other combinations of oral therapy include cefuroxime plus clindamycin or metronidazole, a fluoroquinolone plus clindamycin or metronidazole, sulfamethoxazole and trimethoprim plus clindamycin or metronidazole, penicillin plus clindamycin or metronidazole, and amoxicillin plus clindamycin or metronidazole; a less effective alternative is azithromycin or doxycycline plus clindamycin or metronidazole.[9, 10, 28]
Primate bites, particularly from macaque monkeys, pose a risk of herpes virus B infection.[7] For macaque bites, postexposure prophylaxis with valacyclovir or acyclovir should be given for 14 days after immediate and thorough wound disinfection.[29]
Clinical Context: Levofloxacin is for pseudomonal infections and infections due to certain multidrug resistant gram-negative organisms.
Clinical Context: Metronidazole is an imidazole ring-based antibiotic active against various anaerobic bacteria and protozoa. It is used in combination with other antimicrobial agents (except for C difficile enterocolitis).
Clinical Context: Ampicillin and sulbactam is a drug combination of beta-lactamase inhibitor with ampicillin. It interferes with bacterial cell wall synthesis during active replication, causing bactericidal activity against susceptible organisms.
Clinical Context: The ticarcillin and clavulanate potassium combination inhibits biosynthesis of cell wall mucopeptide and is effective during the stage of active growth. It is an antipseudomonal penicillin plus beta-lactamase inhibitor that provides coverage against most gram-positive organisms, most gram-negative organisms, and most anaerobes.
Clinical Context: Piperacillin and tazobactam sodium combination is an antipseudomonal penicillin plus beta-lactamase inhibitor. It inhibits the biosynthesis of cell wall mucopeptide and is effective during the stage of active multiplication.
Clinical Context: The combination of imipenem and cilastatin is for treatment of multiple organism infections in which other agents do not have wide-spectrum coverage or are contraindicated due to potential for toxicity.
Clinical Context: Ertapenem has bactericidal activity that results from the inhibition of cell wall synthesis and is mediated through ertapenem binding to penicillin-binding proteins. It is stable against hydrolysis by a variety of beta-lactamases, including penicillinases, cephalosporinases, and extended-spectrum beta-lactamases. Ertapenem is hydrolyzed by metallo-beta-lactamases.
Clinical Context: Meropenem is a bactericidal broad-spectrum carbapenem antibiotic that inhibits cell-wall synthesis. It is effective against most gram-positive and gram-negative bacteria. Meropenem has slightly increased activity against gram-negatives and slightly decreased activity against staphylococci and streptococci compared with imipenem.
Clinical Context: Amoxicillin and clavulanate is a drug combination that extends the antibiotic spectrum of penicillin to include bacteria normally resistant to beta-lactam antibiotics. Amoxicillin and clavulanate is first-line therapy for the prophylactic treatment of dog, human, and cat bites (see Medication Summary above). It is also indicated for skin and skin structure infections caused by beta-lactamase–producing strains of Staphylococcus aureus.
Clinical Context: Cefuroxime is a second-generation cephalosporin that maintains gram-positive activity that first-generation cephalosporins have; it adds activity against P mirabilis, H influenzae, E coli, K pneumoniae, and M catarrhalis. The condition of the patient, the severity of infection, and the susceptibility of the microorganism determine proper dose and route of administration.
Clinical Context: Ciprofloxacin is a fluoroquinolone with activity against pseudomonads, streptococci, MRSA, S epidermidis, and most gram-negative organisms, but no activity against anaerobes. It inhibits bacterial DNA synthesis and, consequently, growth.
Clinical Context: Clindamycin is a lincosamide for the treatment of serious skin and soft tissue staphylococcal infections. It is also effective against aerobic and anaerobic streptococci (except enterococci). Clindamycin inhibits bacterial growth, possibly by blocking dissociation of peptidyl tRNA from ribosomes, causing RNA-dependent protein synthesis to arrest.
Clinical Context: Sulfamethoxazole/trimethoprim inhibits bacterial growth by inhibiting the synthesis of dihydrofolic acid.
Clinical Context: Amoxicillin alone is effective against Pasteurella species. However, it is not indicated for skin and skin structure infections caused by beta-lactamase–producing strains of Staphylococcus aureus. A second antibiotic, such as cephalexin, is needed for Staphylococcus infections.
Clinical Context: Azithromycin inhibits bacterial growth, possibly by blocking dissociation of peptidyl tRNA from ribosomes, causing RNA-dependent protein synthesis to arrest. It treats mild-to-moderate microbial infections.
Clinical Context: Doxycycline inhibits protein synthesis and thus bacterial growth by binding to 30S and possibly 50S ribosomal subunits of susceptible bacteria.
Empiric antimicrobial therapy must be comprehensive and should cover all likely pathogens in the context of the clinical setting.
Clinical Context: Acyclovir is a prodrug activated by phosphorylation by virus-specific thymidine kinase that inhibits viral replication. Herpes virus thymidine kinase (TK), but not host cells' TK, uses acyclovir as a purine nucleoside, converting it into acyclovir monophosphate, a nucleotide analogue. Guanylate kinase converts the monophosphate form into diphosphate and triphosphate analogues that inhibit viral DNA replication.
Acyclovir has affinity for viral thymidine kinase and, once phosphorylated, causes DNA chain termination when acted on by DNA polymerase. It has activity against a number of herpesviruses, including herpes virus B. Acyclovir is primarily available in preparations for oral and intravenous use. Patients experience less pain and faster resolution of cutaneous lesions when used within 48 hours from rash onset. Acyclovir may prevent recurrent outbreaks. Early initiation of therapy is imperative.
Clinical Context: Valacyclovir is a hydrochloride salt of the L-valyl ester of acyclovir. It is rapidly converted into acyclovir after prompt absorption from the gut via first-pass intestinal or hepatic metabolism. It is an alternative to acyclovir for prophylaxis (or possibly treatment).
Clinical Context: The vaccine combination tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis vaccine promotes active immunity to diphtheria, tetanus, and pertussis by inducing production of specific neutralizing antibodies and antitoxins. It is indicated for active booster immunization for tetanus, diphtheria, and pertussis prevention for persons aged 10-64 years (Adacel approved for 11-64 y, Boostrix approved for 10-18 y). It is the preferred vaccine for adolescents scheduled for booster.
Clinical Context: The tetanus toxoid vaccine is no longer available in the United States.
It is used to induce active immunity against tetanus in selected patients. The immunizing agent of choice for most adults and children older than 7 years are tetanus and diphtheria toxoids. It is necessary to administer booster doses to maintain tetanus immunity throughout life.
The CDC recommends Td for pregnant patients who have urgent an indication tor tetanus toxoid or diphtheria toxoid vaccination.
In children and adults, it can be administered into deltoid or midlateral thigh muscles. In infants, the preferred site of administration is the mid thigh laterally.
Tetanus results from elaboration of an exotoxin from Clostridium tetani. A booster injection in previously immunized individuals is recommended to prevent this potentially lethal syndrome. Patients who may not have been immunized against C tetani products (eg, immigrants, the elderly) should receive tetanus immune globulin.
Clinical Context: Tetanus immune globulin is used for passive immunization of any person with a wound that might be contaminated with tetanus spores.
Clinical Context: Rabies immune globulin provides passive protection to individuals exposed to rabies virus. About half the dose should be administered into and around the bite wound as much as possible (given anatomic constraints), and the rest given intramuscularly at a site remote from the vaccine administration area in the gluteal or deltoid muscle.
Immune globulins are indicated in previously unvaccinated individuals to provide passive immunity to tetanus when individuals become exposed.
Clinical Context: Rabies vaccine is an inactivated form of virus grown in primary cultures of chicken fibroblasts; it offers active immunity and, when used in combination with human rabies immune globulin (HRIG) and local wound treatment, protects postexposure patients of all age groups; it is also used for preexposure immunization in both the primary series and booster dose.
Fourteen days after initiating immunization series, anti-rabies antibody titers reach levels well abovethe minimal protective level of 0.5 IU/mL.
The vaccine must be injected intramuscularly and never SC, ID, or IV. In adults, inject into the deltoid muscle area. In small children, administer into the anterolateral zone of the thigh.
Clinical Context: Rabies vaccine adsorbed is an inactivated virus vaccine that promotes immunity by inducing active immune response. Rabies vaccine is given intramuscularly only, never intradermally.
Inactivated virus vaccines are inactivated forms of virus that promote immunity by inducing an active immune response.
Animal bites. The devastating damage sustained by a preadolescent male during a dog attack. Almost lost in this photograph is the soft tissue damage to this victim's thigh. This patient required 2 units of O- blood and several liters of isotonic crystalloid. Repair of these wounds required a pediatric surgeon, an experienced orthopedic surgeon, and a plastic surgeon. Attacks such as these have caused a movement in some areas of the country to ban certain dog breeds.
Animal bites. The devastating damage sustained by a preadolescent male during a dog attack. Almost lost in this photograph is the soft tissue damage to this victim's thigh. This patient required 2 units of O- blood and several liters of isotonic crystalloid. Repair of these wounds required a pediatric surgeon, an experienced orthopedic surgeon, and a plastic surgeon. Attacks such as these have caused a movement in some areas of the country to ban certain dog breeds.