The management of domestic animal bites to the hand.
Domestic animal bites to the hand are surprisingly common. An estimated 3.5 to 4.7 million domestic animal bites are reported in the USA each year. (1) Dogs, cats, ferrets, snakes, and birds are common pets and are the most frequent sources of these injuries. Multiple studies cite the hand and upper extremity as the most common locations for animal bites. (1,2)
Epidemiology and Clinical Presentation Dogs
In ancient Egypt, dogs were so revered that after death their bodies were embalmed and mummified by their masters. But, man's best friend was not always so friendly. Dog bites represent 80 to 90% of domestic animal bites. (3) Hand bites from a domestic dog are more common in children under 10 years of age, and over 50% of all dog bites are located in the hand and forearm. (1,3) The infection rate has been reported between 2 to 20%, which is relatively low risk among mammals. (12)
The jaws of dogs are strong and capable of exerting 150 to 450 lbs/[inch.sup.2] of force. (3,4) Their teeth are blunt and broad and cause injury by crushing and shearing. This mechanism can cause significant soft tissue damage.
Like dogs, cats were first domesticated in ancient Egypt. Their quick and stealth movements were praised for controlling vermin. Cat bites represent 5% to 15% of all pet bites. In contrast to their canine counterparts, their bites are more common in adults. Two-thirds of these bites affect the hand and account for infections rates between 30% to 80%. (1) A significant number of these patients will require hospital admission (37%) and surgical management (12%). (5)
The anatomy of cat teeth contributes to the significant morbidity induced by their bites. Razor sharp and small, cat teeth can create fine puncture wounds that heal quickly and entrap bacteria. They can also efficiently inoculate small joints, deep spaces, or tendon sheaths of the hand. The appearance of these wounds is typically benign initially, and many wind up presenting late for medical evaluation.
Ferrets are the 3rd most common household pet in the USA. Close cousins to weasels, the domestic ferret has increased in popularity with approximately 7 to 10 million households owning them as pets. (6) Ferrets are small and tend to attack young infants or newborns. More bites have been recorded to the face than the extremities with 28% of their victims requiring plastic or reconstructive surgery. (6)
Ferret teeth are small and sharp like the cat but they unleash rapid fire bites. It is not uncommon to have to pry the ferret from their prey. As they can maneuver in and out of households into the wild and back into the home, they can be reservoirs for rabies. Fortunately, there are no reports of humans contracting rabies from ferrets, though 22% of victims required rabies prophylaxis after ferret bites. (7) The high mortality of rabies makes urgent treatment and reporting of ferret bites extremely important.
Snakes are also common household pets. There are 50,000 reported snake bites per year of which 7,000 are venomous. (8) The 15 fatalities reported per year worldwide most commonly involve the king cobra snake. Ninety percent of these injuries are distal to the elbow and knee. (9)
"Exotic" snakes, such as the king cobra, are not indigenous to the USA, but many are bought on the black market. The two earliest and most common manifestations of cobra bites include ptosis and drowsiness. There are two types of venomous snakes indigenous to the USA: the pit viper and coral reef snakes. Their bites may be neurotoxic or cause rapid onset systemic shock, respectively. The bite of poisonous snakes have characteristic marks that leave small puncture wounds in front of larger indentations created from their back teeth. Common presentations for pit viper envenomation are local edema, hypotension, and ultimately myonecrosis. (9) Coral reef bites have minimal local effect but can cause paralysis of respiration and swallowing and ultimately muscle paralysis and death. (9) Respiratory distress is a late and often fatal sign if treatment has not been initiated.
Contrary to big screen depictions, incision and suction in the field is not indicated, but quick action must be taken. Immobilization, application of a non-constricting band distal and proximal to the bite and quick transport to a hospital must be done quickly. (9) Large bore intravenous access, hydration, tetanus prophylaxis, broad spectrum antibiotics, and compartment pressure monitoring should be started. Access to an antivenin for systemic symptoms is arguably the most important for survival, and therefore immediate transfer to a hospital is critically important. (10)
There are 6.4 million households that own at least one pet bird, the vast majority of which are parrots, cockatiels, or parakeets. (11)
Parrot beak bites can resemble a cat's tooth and inflict similar damage as they can exert a force up to 200 pounds per square inch. (11) Most common bird beak injuries include nail bed injuries, open fractures, and distal amputations. (11)
The hand is constantly exposed to a significant amount of bacteria. The fingernail hyponychium has a higher concentration of lymphatics than any other dermal region of the body. (12) Though humans are highly protected against infection by various features, the risk of hand infection is increased by the unique anatomy. Tendons, potential spaces, and joints lie beneath the skin and allow easy access for inoculation of deep structures. (13)
There are a number of infections than can develop in the hand after a domestic animal bite. In addition to local abscesses, a hand bite from a domestic animal puts one at risk for deep space infections, pyogenic flexor tenosynovitis, septic arthritis, and osteomyelitis. (14)
Deep Spaces Infections
Deep spaces of the hand include the thenar, midpalmar, and hypothenar spaces. The clinical relevance is that these spaces can act as conduits for infection to travel through the hand and forearm. For example, the thenar and hypothenar sheaths extend proximally into the palm and can communicate with radial and ulnar bursae that can allow infection to spread from the radial to the ulnar side of the hand and vice versa. This type of infection is commonly referred to as a "horseshoe abscess." The communication of infection between the radial and ulnar bursae occurs most often when the infection tracks into the wrist in the space between the pronator quadratus and the overlying flexor tendons of the forearm (Parana's space). If not treated properly, infection of these spaces can progress to become lymphangiitis, septic arthritis, tenosynovitis, or osteomyelitis. (2)
Pyogenic Flexor Tenosynovitis
The flexor tendons are encased in a fibro-osseous tunnel and are particularly vulnerable to infection given their unique blood supply. Flexor tendons receive nutrition from diffusion and through the vincular system.
Clinically, it is important to understand the Kanavel signs as flexor tenosynovitis is a surgical emergency and should be diagnosed quickly and treated immediately. These signs include pain on extension, fusiform swelling, flexed posture of the digit, and tenderness along the tendon sheath. Pain on passive extension is thought to be the most reliable sign. (15) Pyogenic flexor tenosynovitis is a clinical diagnosis and must be differentiated from conditions such as herpetic whitlow. Oftentimes an aspiration of the flexor tendon sheath at the level of the A1 pulley can assist in the diagnosis if purulent fluid is aspirated. In addition, this fluid can be sent for culture and sensitivities while empiric antibiotics are initiated. If antibiotics are initiated early, some patients can be followed clinically and will not require surgical incision and debridement. If the infection is left untreated, destruction of the tendons and fibro-osseous sheath can ensue, which would require extensive debridement and staged tendon and sheath reconstruction. Prompt clinical diagnosis and surgical treatment can prevent tissue destruction and associated complications.
Osteomyelitis and Septic Arthritis
Osteomyelitis is uncommon in the hand, accounting for only 5% of all hand infections. Fifty-seven percent of these cases occur secondary to contaminating injuries, such as direct inoculation. (16) Plain radiographs typically do not demonstrate changes until weeks later, and laboratory studies are not always reliable. Common plain film findings include osteolysis (70%), osteopenia (10%), and periosteal reaction. A sequestrum or involucrum will only be seen in 10% of cases. (17)
A thorough clinical examination is extremely important when a patient presents with an animal bite to the hand.
A thorough history includes obtaining the exact time of the bite, type of animal, whether the owner is known, and vaccination status of the animal. The patient should be interviewed about history of medical comorbidities, such as splenectomy, rheumatoid arthritis, diabetes, and HIV. Use of immunosuppressants, such as systemic corticosteroids, can help identify patients at increased risk of infection. Other risk factors for infection include age greater than 50 years, diabetes, and treatment delay greater than 24 hours. (7) An effort should be made to obtain behavior patterns of the animal prior to the bite and the vaccination status.
Physical examination should include vital signs to rule out sepsis, and the severity of the wound should be determined. Simple lacerations from a dog have a decreased risk of infection than a puncture wound inflicted by a cat. (1) Nygaard and coworkers found that dog bites can result in significant morbidity, including tendon, neurovascular, bone, and skin loss requiring operative management. (3)
The physical examination should include active and passive motion of the hand and all digits, vascular status, changes in sensibility, palpation for any retained foreign bodies, areas of fluctuance, or areas of significantly increased compartment pressures. The presence of erythema or streaking lymphangitis seen tracking proximally suggests a systemic infection. Immediate intravenous antibiotics or surgical irrigation and debridement may be warranted if there is an area of focal collection. Due to the superficial nature of the majority of bites, an emergency room bedside surgical incision and drainage is usually adequate to decrease the bacterial load in the region. If the patient fails to clinically improve, a formal treatment in the operating room may be warranted for a more thorough debridement.
Laboratory Studies and Imaging
In the setting of a hand bite, plain radiographs should always be obtained to rule out fractures, dislocations, and foreign bodies. If air is noted within the soft tissues, urgent evaluation must be undertaken to prevent a compartment syndrome and potential spread of potent bacteria.
Baseline white blood cell count, erythrocyte sedimentation rates (ESR), and C-reactive proteins (CRP) should be obtained to establish presence of an acute infection and to monitor the effectiveness of treatment. It is important to note that negative inflammatory labs do not preclude the presence of osteomyelitis or septic arthritis. (17)
Microbiology (Table 1)
Dogs and Cats
In a 1999 New England Journal of Medicine article, Talan and colleagues prospectively looked at 50 patients infected with cat or dog bites and cultured the wounds. They found that Pasteurella species was the most common isolate from cats (75%) and dogs (50%). In addition, they determined that many patients were receiving prophylactic antibiotics for hand bites that did not cover Pasteurella. A beta-lactamase combined with a beta-lactam inhibitor (i.e., amoxicillin and clavulanic acid) or trimethoprim/sulfamethoxazole (TMPSMZ) for the penicillin allergic is the recommended regimen.
Hand bites that are not adequately treated can progress and cause significant morbidity. In addition to the immunocompromised, there have been numerous reports of patients with total hip and knee replacements that sustained deep pet bites and developed subsequent septic joints. Most of the patients had significant comorbidities (i.e., diabetes, chronic steroids, immunosuppressed). (18) They concluded that antibiotics should be given to these patients after a domestic animal bite. Mehta and Mackie and associates advocated telling patients with prosthetic joints, particularly if immunocompromised, about the significant risk of infection if bitten by a pet animal. (18) Kadakia and coworkers went further and recommended that all patients should be warned of the risks of infection prior to receiving a total joint replacement. (19)
The fecal microflora of ferrets includes Campylobacter and Salmonella as well as other less common species. (20) Though ferrets can harbor many bacteria, rabies should be the primary concern of the clinician due to its morbidity. Ferrets are small and can easily leave their home and become infected in the wild. There is a theoretical risk of human transmission once the ferret returns home if a bite occurs. There have been 13 cases reported of feral rabies in the USA. (21) There are no cases of human transmission. Rabies infection should be in the forefront of the clinicians' mind when a patient presents with a history of a ferret bite.
Infection after a bird bite is rare. Most zoonoses associated with birds are acquired through the respiratory system. Patients present clinically with atopy or asthma most commonly. (7) The microbiology of the birds mouth is a mixed flora with E. Coli, Staphylococcus, Pasteurella, Salmonella, and Proteus species being most common. (11) Rabies and subsequent quarantine is not a concern after a pet bird bite. Subsequent infection is rare, and antibiotic coverage is guided by clinical symptoms. Broad spectrum antibiotics that include Pasteurella coverage can be prescribed initially and oral ciprofloxacin added if the patient is not improving clinically. (7)
General Wound Management
All open wounds should undergo cleansing in the emergency room using at minimum soap and sterile water to reduce the inoculum of oral flora bacteria as well as decrease the risk of rabies transmission. (2) Alternatively, Roberts and coworkers showed that Povidone-iodine prior to suturing hand lacerations significantly decreased risk of wound infection and imperfect healing. (22) Injuries below the dermis are known risk factors for infection (23) and thus should undergo thorough inspection, debridement, and irrigation.
For all domestic animal bites, tetanus immune globulin and tetanus toxoid should be administered if the patient has received two or fewer primary immunizations. Tetanus toxoid alone can be given if they have completed primary immunizations but have not had a booster in the last 5 years.
Rabies is a negatively stranded RNA virus that is spread through the saliva of infected hosts and can cause a fatal encephalitis in humans. Between 1980 and 1996, there have been 32 human cases in the USA. (21) Due to an increase in vaccination rates, the risk of rabies after a domestic animal bite is low. Twelve percent of all rabies cases are through domestic animals. (4,24) Presenting signs include fever, pain at bite site, and sensory changes. These findings can quickly progress to neurologic problems due to muscle paralysis and ultimately death.
All domestic animals behaving wildly with aggression or licking at the site of a bite should be put to sleep to evaluate the brain. Healthy appearing dogs, cats, and ferrets can be monitored for 10 days. If signs of aggression appear, then they should be sacrificed and brains examined. Human rabies vaccine should be administered if the animal tests positive for rabies or is not captured and cannot be observed. (25)
Antibiotics (Table 2)
In a 2010 meta-analysis, Medeiros and colleagues found that there is no apparent advantage to antibiotic prophylaxis in simple dog bites. Wound type did not appear to influence the rate of infection. (26)
When treating a domestic animal hand bite (cats, dogs, ferrets, and birds) for an infection, oral amoxicillin and clavulanic acid is recommended. A single parental dose of a beta-lactam and beta-lactamase inhibitor (i.e., piperacillin-tazobactam) can be given in the emergency room. It is important to know that ampicillin/sulbactam does not provide Pasteurella coverage and should not be used in these scenarios. In addition, first generation cephalosporins alone are not adequate. (27) Fluoroquinolones or TMP-SMZ can be given for the adult with a penicillin allergy. Children with penicillin allergies can be prescribed doxycycline.
There are no clear guidelines for the treatment after a bird bite, but in general patients are given broad spectrum antibiotics.
Maimaris and associates in a prospective, randomized study showed that sutured hand wounds have a significant increase in infection rates. (28) They also found that a delay in presentation greater than 10 hours and smaller wounds left unsutured had increased infection risk. It is thought that the latter can be explained due to poor cleansing of a benign appearing wound. This illustrates the importance of a thorough debridement and cleansing of bite wounds. (28)
The literature supports closing fresh facial bites because of the low risk of infection and cosmetic concerns. (29)
The only bite wounds of the hand that should be closed are simple dog lacerations presenting within 24 hours after the bite. (4,18) In addition, these patients should be followed closely. Puncture wounds should have marginal excision as the wounds tend to heal quickly and can entrap bacteria. All hand wounds, dog bite wounds with delayed presentation, cat bites, and puncture wounds should be allowed to heal by secondary intention with secondary closure held in reserve only for large wounds after a thorough debridement and sterile appearing wound bed.
In general, all bite wounds of the hand that appear infected should undergo a surgical incision and debridement for any focal collections. If warranted, this may proceed in the emergency room setting for a superficial abscess, but if a deep infection is suspected, the patient should go immediately to the operating room for a formal irrigation and debridement with cultures. Elevation, tetanus, and antibiotic prophylaxis (beta-lactamase and beta-lactam inhibitor, i.e., Augmentin) is recommended for benign wounds, such as cellulitis without a focal collection. Always consider the need for rabies prophylaxis. If the wound is swollen, tender, erythematous, or if the patient demonstrates painful range of motion, an admission is warranted for splinting, elevation, and intravenous antibiotics. If there is no improvement in 24 hours, then appropriate antibiotic coverage should be scrutinized, and a formal irrigation and debridement should be considered for the next step in management. Grossly infected wounds should be cultured, and the patient placed on broad spectrum IV antibiotics until cultures have isolated an organism. If the wound does not appear to improve or if there is systemic infection with sepsis, a "second look" is warranted in 24 to 48 hours for an additional irrigation and debridement. Wounds are left open and can be changed daily with wet to dry dressings. (7,23) Serial CRP should be used in addition to clinical signs to monitor for clinical improvement.
Hand bites from domestic animals are extremely common. Though many may initially appear benign, it is important for patients to be aware of the factors that place them at additional risk for infection. As clinicians, we must be able to efficiently diagnose and treat these patients properly to avoid the morbidity that these bites can provoke.
None of the authors has a financial or proprietary interest in the subject matter or materials discussed in the manuscript, including, but not limited to, employment, consultancies, stock ownership, honoraria, and paid expert testimony.
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(28.) Maimaris C, Quinton DN. Dog-bite lacerations: a controlled trial of primary wound closure. Arch Emerg Med. 1988 Sep;5(3):156-61.
(29.) Stefanopoulos PK, Tarantzopoulou AD. Facial bite wounds: management update. Int J Oral Maxillofac Surg. 2005 Jul;34(5):464-72.
R. Damani Howell, M.D., Resident, Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, New York. Anthony Sapienza, M.D., Assistant Professor of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, New York.
Correspondence: Anthony Sapienza, M.D., 530 FirstAvenue, New York, New York 10003; firstname.lastname@example.org.
Table 1 Microbiology Domestic Animal Most Common Species Isolated Dogs Pasteurella spp., Staphylococcus, Streptococcus (28) Cats Pasteurella spp., Staphylococcus, Streptococcus (28) Ferrets Salmonella (6,200 Birds E. Coli, Staphylococcus sp., Pasteurella multocida (11) Table 2 Antibiotics Patient type Antibiotic Outpatient Amoxicillin-clavulanate (PO) Inpatient Piperacillin tazobactam (IV) Penicillin allergic Doxycycline (PO,IV) or TMP-SMZ