Animal bites (dogs, cats, and other mammals): Evaluation and management

INTRODUCTION — Bites from mammals may be associated with significant morbidity. Complications include infection and injury to deep structures.

The evaluation and management of mammalian bites and infected wounds are discussed here. The following are discussed separately:

●Zoonoses from dogs and cats (see "Zoonoses: Dogs" and "Zoonoses: Cats" and "Capnocytophaga" and "Pasteurella infections" and "Microbiology, epidemiology, clinical manifestations, and diagnosis of cat scratch disease")

●Evaluation and management of human bite wounds (see "Human bites: Evaluation and management")

●Snake and arthropod bites (see "Snakebites worldwide: Clinical manifestations and diagnosis" and "Snakebites worldwide: Management" and "Bites by Crotalinae snakes (rattlesnakes, water moccasins [cottonmouths], or copperheads) in the United States: Clinical manifestations, evaluation, and diagnosis" and "Bites by Crotalinae snakes (rattlesnakes, water moccasins [cottonmouths], or copperheads) in the United States: Management" and "Insect and other arthropod bites" and "Diagnostic approach to the patient with a suspected spider bite: An overview")

●Evaluation and management of infected puncture wounds (see "Infectious complications of puncture wounds")

EPIDEMIOLOGY — Animal bites are common worldwide. In North America, two to five million animal bites occur annually, which account for about 1 percent of emergency department visits and 10,000 annual inpatient admissions [1-3].

●Dog bites – These account for approximately 90 percent of animal bites (rate of 103 to 118 per 100,000 population) in the United States [4]. Most dog bite victims are children, with the highest number in boys between five and nine years of age [5-9]. Fatalities are rare but disproportionately affect children younger than 10 years of age [10,11].

In resource-limited regions, bites by stray dogs are more common causes of rabies transmission than bites from any other animal. (See "Clinical manifestations and diagnosis of rabies", section on 'Animal reservoirs'.)

●Cat bites – These account for approximately 10 percent of animal bite wounds in the United States, and occur most often in adult women [7]. Cat bites are responsible for most emergency department visits for seriously infected bite wounds [12,13].

●Bites from other mammals – Bites from mammals other than cats and dogs are uncommon. Pets are often the source of such bites.

EVALUATION — Following a bite wound, patients may seek care for evaluation of the bite injury itself, for infection, or for concern about rabies or tetanus.

Obtaining a history — We ascertain the patient’s symptoms, including any indicators of infection (eg, fever), neurovascular compromise (eg, weakness, numbness, excessive bleeding), alteration in function (eg, decreased range of motion), and risk for wound infection, rabies, and tetanus.

In addition, we assess the following, which may change the risk for wound infection and serious injury:

●Type of animal (eg, dog, cat) – Dog bites are associated with a range of injuries, from minor wounds (eg, scratches, abrasions) to major wounds (eg, gaping lacerations, deep puncture wounds, tissue avulsions, and crush injuries) (picture 1) [7,14]. In particular, the jaws of large dogs, such as pit bull terriers, German shepherds, and Rottweilers, can exert a strong force that may inflict serious injury and damage underlying structures [15,16].

Cat bites tend to penetrate deeply with higher risk of deep infection (abscess, septic arthritis, osteomyelitis, tenosynovitis, bacteremia, or necrotizing soft tissue infection) than dog bites [7,12,13,17,18]. For example, in a retrospective series that included more than 2500 dog bites and almost 1000 cat bites, infection rates were 7 and 49 percent, respectively [13].

Certain bites (eg, primates, rodents) may warrant special consideration in addition to typical management. (See 'Bites from mammals other than dogs and cats' below.)

●Anatomic location of bite(s) – The hand, especially the dominant hand, is the most common site of dog bites in adults and cat bites in people of all ages [10,19]. In young children, the head is the most common site of dog bites.

Fatalities from bites are rare, and usually occur in young children with dog bites involving the head and neck or direct penetration of vital organs. Head injuries in children may penetrate the skull, resulting in depressed skull fracture, local infection, and/or brain abscess [20,21].

●Time elapsed between the bite and presentation for care – Delayed presentation (≥12 hours after a bite on the extremities and ≥24 hours after a bite on the face) increases risk of infection [4,22].

●Medical conditions that increase risk of infection – These include immunocompromise (eg, diabetes mellitus, asplenia), liver disease (eg, cirrhosis), alcohol use disorder, foreign implants (eg, prosthetic joints, vascular grafts), and prior cellulitis or lymphatic/venous compromise in affected extremity.

In addition to the type of animal, essential information to determine need for rabies and tetanus post-exposure prophylaxis includes the following:

●Information about the patient

•Date of last tetanus vaccine

•Dates of prior rabies vaccinations or exposures

•Geographic location at the time of the bite (rabies is rare in the United States but more common in other parts of the world)

●Information about the animal

•Whether the bite was provoked or unprovoked

•Whether the animal is wild, domestic, or stray

•Current location of animal

•Whether the animal is still alive and available for observation

•Rabies vaccination history of animal

•Health status of animal – recent behavioral changes (eg, confusion, unsteady gate, aggression, or foaming at the mouth)

Further details regarding risk assessment of rabies and tetanus are found separately. (See "Indications for post-exposure rabies prophylaxis" and "Tetanus-diphtheria toxoid vaccination in adults".)

Some patients can be managed at home without immediate evaluation by a clinician, such as those who report a superficial abrasion and have no indication for rabies or tetanus prophylaxis. They should be instructed to wash their wound at home. (See 'Wound preparation' below.)

Inspecting the wound

Wound preparation — Upon presentation, bite injuries are cleansed to facilitate examination, allow for adequate visualization of the extent of injury, and prevent infection. Appropriate wound management is the most important factor for preventing infection and is of paramount importance for preventing rabies [7].

Initial wound preparation includes the following steps (algorithm 1):

●Control bleeding (direct pressure should be applied to actively bleeding wounds).

●Clean wound with soap and water, or an antiseptic solution (eg, povidone iodine).

●Irrigate with tap water or sterile saline and remove grossly visible debris (if present).

Cleaning the wound is often better tolerated in patients who present immediately after the bite compared with patients who have an infected wound. For patients with significant pain, local anesthesia may be required to facilitate initial wound care, as discussed separately. (See "Subcutaneous infiltration of local anesthetics" and "Clinical use of topical anesthetics in children".)

Detailed discussion of initial wound preparation is found separately. (See "Minor wound evaluation and preparation for closure".)

Physical examination — Once the wound has been cleaned and bleeding is controlled, examine for the following (algorithm 1) (see "Minor wound evaluation and preparation for closure", section on 'Evaluation'):

●Proximity of bite to joints, tendons, or bone, and potential injury to adjacent structures. Full range of motion of nearby joints should be assessed; wound proximity to a joint may not be apparent without testing full range of motion, and pain in the joint may be indicative of joint violation or infection.

●Evidence of neurovascular compromise distal to the wound. 

●Depth of wound. We consider a deep wound to be one that has penetrated the dermis into subcutaneous tissue (figure 1). However, depth may be difficult to fully assess for a puncture wound, which is generally defined as a wound with a depth greater than width.

●Retained foreign material (eg, tooth).

●Approximation of the wound edges (eg, the edges of a wound with tissue loss may not align cleanly or with minimal tension).

●Potential cosmetic significance of a scar if wound is not closed primarily (eg, wound on face, large gaping wound).

●Signs of infection, as discussed immediately below.

Assessing for infection — Infection can cause significant morbidity after dog and cat bites. Among patients who receive care in emergency departments, observational data suggest that 5 to 16 percent of dog bites and half of cat bites are infected [4,12,13,22-26].

Onset of signs and symptoms — Infection is unlikely in patients who present for care immediately after the bite.

The median time to signs and symptoms of infection following a dog bite is approximately 24 hours [27].

For cat bites, the median time to onset of infection is typically shorter (ie, approximately 12 hours); infections apparent within hours of a cat bite have been described [27].

Types of infection

●Cellulitis – This is an infection of the deep dermis and subcutaneous fat. Clinical manifestations include erythema, tenderness, swelling, and warmth; fever, purulent drainage, or lymphangitis may be present (picture 2).

In the absence of fever, it can be difficult to distinguish cellulitis from expected inflammation following a wound. Given the incidence and morbidity of bite-related infections, we generally have a low threshold to attribute erythema to infection.

The clinical presentation of cellulitis is discussed in detail separately. (See "Cellulitis and skin abscess: Epidemiology, microbiology, clinical manifestations, and diagnosis", section on 'Clinical manifestations'.)

●Abscess – Abscesses associated with bite wounds can be superficial or deep. Superficial abscesses typically present as tender, fluctuant, erythematous nodules; when associated with bites, superficial abscesses typically have surrounding cellulitis. Deep abscesses may present with pain, tenderness, and induration without obvious fluctuance or skin erythema.

●Flexor tenosynovitis – This condition requires prompt recognition and surgical debridement because an infection of the finger flexor tendons can spread rapidly along the sheath compartments into the hand and forearm. Bite wounds to a finger are the most common etiology; the flexor tendons are preferentially involved.

The cardinal signs of flexor tenosynovitis are tenderness along the course of the flexor sheath, symmetric or fusiform enlargement of the affected digit, slight flexion of the digit at rest, and pain along the tendon with passive extension (picture 3).

Detailed discussions of infectious tenosynovitis and hand infections are found separately. (See "Infectious tenosynovitis" and "Overview of hand infections".)

●Necrotizing soft tissue infection (eg, fasciitis) – This limb- and life-threatening condition can be challenging to diagnose, but it is rapidly progressive and requires prompt surgical debridement.

Clinical features of necrotizing soft tissue infections include the following:

•Rapidly progressive pain

•Pain out of proportion to skin exam findings

•Crepitus

•Brawny induration

•Systemic signs such as fever >100.5°F/38°C, hypotension, and/or sustained tachycardia 

•Persistent or progressive signs of infection despite initial wound care and appropriate antibiotic administration

Diagnosis of necrotizing soft tissue infections is discussed in detail separately. (See "Necrotizing soft tissue infections", section on 'Clinical manifestations' and "Necrotizing soft tissue infections", section on 'Diagnosis'.)

●Septic arthritis or osteomyelitis – These infections can occur if the initial bite penetrated bone or a joint space, or if soft tissue infection spreads to bone or joint.

Septic arthritis should be suspected in a patient with a joint effusion, warmth, or pain with passive movement of an involved or adjacent joint. Osteomyelitis is often challenging to diagnose and should be suspected if the bite was over a bone and pain, tenderness, erythema, or swelling progress despite appropriate oral antibiotic therapy.

Joints or bone that are penetrated by the initial bite should have prompt surgical consultation, regardless of whether other signs of infection are present.

Diagnosis of septic arthritis and osteomyelitis is discussed in detail separately. (See "Septic arthritis in adults", section on 'Clinical manifestations' and "Septic arthritis in adults", section on 'Diagnosis' and "Prosthetic joint infection: Epidemiology, microbiology, clinical manifestations, and diagnosis", section on 'Clinical manifestations' and "Prosthetic joint infection: Epidemiology, microbiology, clinical manifestations, and diagnosis", section on 'Diagnosis' and "Nonvertebral osteomyelitis in adults: Clinical manifestations and diagnosis".)

Although the above infections are localized, they may also cause bacteremia or sepsis that can present as systemic illness (eg, fever >100.5°F/38°C, hypotension, sustained tachycardia, confusion).

Ancillary tests

Imaging — We typically obtain imaging in all patients with a mammal bite, except for those with a clinically uninfected, superficial dog bite (algorithm 1).

In most cases, plain radiographs are sufficient to detect retained foreign bodies (eg, embedded teeth) or fracture (picture 4) but are not sensitive for detecting joint involvement. They can also detect subcutaneous gas, which is sometimes (but not always) present in necrotizing soft tissue infection.

If a superficial abscess is suspected, point-of-care ultrasonography can aid with diagnosis and facilitate drainage. (See "Techniques for skin abscess drainage", section on 'Bedside ultrasonography'.)

If there is concern for deeper infection (eg, deep abscess, pyomyositis, osteomyelitis), magnetic resonance imaging (MRI) is the optimal technique. Computed tomography (CT) with intravenous contrast may be helpful if MRI is not immediately available. Plain radiographs and bone scans are less helpful. (See "Primary pyomyositis", section on 'Radiographic imaging' and "Approach to imaging modalities in the setting of suspected nonvertebral osteomyelitis", section on 'Selecting an imaging modality'.)

In children <3 years with a dog bite to the scalp associated with a wound of uncertain depth, CT of the head may be useful to evaluate for penetrating injury of the skull [21,28]. CT findings may include skull fracture, puncture through the outer plate of the skull, or free air in the cranial vault.

Cultures (wound, blood)

●Wound cultures – In patients with suspected infection, wound Gram stain and cultures, aerobic and anaerobic, should be obtained to identify the causative pathogen(s) and to guide antibiotic therapy. Specimens should be obtained at the time of debridement (preferably prior to initiation of antibiotics) and samples sent for both aerobic and anaerobic bacterial cultures. The microbiology laboratory should be notified that an animal bite wound is the source, so they can use specific techniques to identify fastidious organisms, such as P. multocida.

In patients with clinically uninfected bite wounds, we do not obtain wound cultures because the results do not correlate with infection [4,22,29].

●Blood cultures – We obtain blood cultures in patients with fever or other signs of systemic infection, and in immunocompromised patients with any signs of infection [22,30]. In patients without evidence of systemic infection, the yield of blood cultures is low, and the risk of false positives (eg, skin contamination) typically outweighs the benefit.

Limited role of laboratory tests — In patients with clinically uninfected bite wounds, we do not obtain laboratory tests.

In a patient in whom we suspect a serious infection (eg, fasciitis), we obtain a complete blood count with differential and sepsis markers (eg, C-reactive protein, lactate) per institutional protocols. For patients with mild infection and no evidence of systemic illness, the value of these tests is less certain; in some cases, laboratory abnormalities may be a deciding factor in determining the need for further observation or hospital admission. Laboratory findings are nonspecific, but may include leukocytosis, neutrophilia, a left shift, or elevated inflammatory markers.

MANAGEMENT

Rabies and tetanus post-exposure prophylaxis — All patients with a mammalian bite require evaluation for rabies and/or tetanus post-exposure prophylaxis. The prevalence of rabies and tetanus varies geographically, but both infections can be fatal if prophylaxis is not provided when indicated. (See "Tetanus" and "Rabies immune globulin and vaccine" and "Treatment of rabies".)

We begin the prophylactic regimen during the initial visit (algorithm 1). If prophylaxis is indicated but unavailable, the patient should be transferred to a facility that can provide these.

●Rabies – Bites are the primary method of transmission to humans since the rabies virus is carried in the saliva of rabid animals. In patients bitten by potentially rabid animals, early and vigorous cleansing with soap and water for 15 to 20 minutes is recommended in expert guidelines, along with timely administration of rabies immune globulin and vaccine [31-33]. (See 'Wound preparation' above.)

Indication for prophylaxis depends on the type of animal bite and wound (algorithm 2). All patients with an indication for rabies prophylaxis should receive a rabies vaccine series; in addition, most will require rabies immune globulin (table 1). Issues related to rabies prophylaxis are discussed in further detail separately. (See "Indications for post-exposure rabies prophylaxis" and "Rabies immune globulin and vaccine".)

The United States Centers for Disease Control and Prevention provides guidance regarding the risk for rabies and the need for postexposure prophylaxis based on type of animal exposure. (See "Indications for post-exposure rabies prophylaxis" and "Rabies immune globulin and vaccine".)

●Tetanus – Animal bites are considered a tetanus-prone wound. In a fully vaccinated patient (ie, has had ≥3 doses of a tetanus toxoid-containing vaccine), administer a tetanus toxoid-containing vaccine only if their last dose was given ≥5 years ago (or if the date of their most recent vaccine is uncertain) (table 2). In an unvaccinated or partially vaccinated patient, administer a tetanus toxoid-containing vaccine and tetanus immune globulin.

Further details about tetanus vaccination are found separately. (See "Tetanus-diphtheria toxoid vaccination in adults" and "Diphtheria, tetanus, and pertussis immunization in children 6 weeks through 6 years of age" and "Diphtheria, tetanus, and pertussis immunization in children 7 through 18 years of age".):

Infected dog and cat bites — In addition to possible rabies and tetanus prophylaxis, infected bite wounds are managed with antibiotic therapy, obtaining cultures, and wound debridement (if needed) [22,34].

Antibiotic therapy

Choosing oral versus IV therapy — Oral antibiotic therapy is effective for most patients with infected wounds.

In the following circumstances, we administer intravenous (IV) antibiotics:

●Sepsis

●Rapidly progressive (eg, over hours) erythema

●Progression after 48 hours of appropriate oral antibiotics

●Deep-space infection (eg, necrotizing fasciitis, septic arthritis)

●Proximity of the bite to an indwelling device (eg, prosthetic joint, vascular graft)

In a patient who has lymphangitis or an immunocompromising condition, we have a lower threshold for choosing IV therapy because these patients may be at increased risk for rapid or systemic progression of their infection.

In a patient who presents to the emergency department with an infected wound but does not meet the above criteria, some experts will administer one IV antibiotic dose followed by oral therapy. This practice may provide more rapid attainment of therapeutic blood antibiotic concentrations, but evidence does not exist that it improves outcomes.

Oral regimens — For oral treatment of infected dog and cat bites, we suggest one of the following antibiotic regimens (algorithm 1):

●Preferred agent – We prefer amoxicillin-clavulanate (875/125 mg orally every 12 hours in adults; see table for pediatric dosing) (table 3).

This regimen covers the most frequently isolated organisms from infected dog and cat bites and is well tolerated in most patients. (See 'Spectrum of antibiotic coverage' below.)

●Alternative regimens – For a patient unable to take amoxicillin-clavulanate, we suggest combination therapy with one agent that covers aerobic bacteria and another that covers anaerobes.

For patients intolerant of all beta-lactams, our favored regimen is trimethoprim-sulfamethoxazole (1 double-strength tablet twice daily) plus metronidazole (500 mg orally every 8 hours), based on clinical data for cellulitis (see "Acute cellulitis and erysipelas in adults: Treatment", section on 'Alternatives for serious beta-lactam allergy'). Additional options are listed in the table, and selection may depend on the antibiotics’ adverse effects (table 3). Many patients with reported beta-lactam allergies can still take a cephalosporin, as discussed in detail separately (algorithm 3).

We do not provide empiric coverage against methicillin-resistant Staphylococcus aureus (MRSA) except in patients with abscess, MRSA risk factors (table 4 and table 5), or gram-positive cocci in clusters on Gram stain of the wound. Our preferred regimen for MRSA coverage is combination therapy with amoxicillin-clavulanate (875 mg orally every 12 hours) plus either trimethoprim-sulfamethoxazole (1 double-strength tablet orally every 12 hours) or doxycycline (100 mg orally every 12 hours). Other antibiotics that cover MRSA are noted in the table (table 3). Issues related to risk factors and treatment of MRSA are discussed further separately. (See "Methicillin-resistant Staphylococcus aureus (MRSA) in adults: Treatment of skin and soft tissue infections" and "Methicillin-resistant Staphylococcus aureus (MRSA) in adults: Epidemiology".)

Although clindamycin is an option for anaerobic coverage, we generally avoid it due to risk of Clostridioides difficile infection. We also do not use it as monotherapy for aerobic coverage since it has poor activity against Pasteurella spp, and streptococcal and staphylococcal resistance is possible, as discussed separately. (See "Acute cellulitis and erysipelas in adults: Treatment", section on 'Alternatives for serious beta-lactam allergy'.)

Doxycycline has some coverage against anaerobic bacteria, but data are scarce regarding its activity against bite-associated anaerobic bacteria. When using doxycycline for infected bites, we add an additional agent for anaerobic coverage; for prophylaxis of uninfected bites, some clinicians use it without adding additional anaerobic coverage [1].

For bites from mammals other than cats and dogs or bites exposed to unique environments, regimens against additional pathogens may be indicated, as discussed below. (See 'Bites from mammals other than dogs and cats' below and 'Spectrum of antibiotic coverage' below.)

Data from clinical studies are limited, and our antibiotic selections are primarily based on the typical microbiology of infected bite wounds. (See 'Spectrum of antibiotic coverage' below.)

Intravenous regimens — Our criteria for IV antibiotics are described above. (See 'Choosing oral versus IV therapy' above.)

Our preferred IV regimen for cat and dog bites is one of the following (table 6):

●Ampicillin-sulbactam (3 g IV every 6 hours in adults)

●Ceftriaxone (2 g IV once daily in adults) plus metronidazole (500 mg IV every 8 hours in adults)

We add intravenous vancomycin to cover MRSA in patients who have severe illness, abscess, MRSA risk factors (table 4 and table 5), or gram-positive cocci in clusters on Gram stain of the wound.

For patients with necrotizing skin infection (eg, fasciitis), empiric antibiotic coverage is typically broader and targets toxin. Necrotizing skin infections are discussed in detail separately. (See "Necrotizing soft tissue infections", section on 'Treatment'.)

Once a patient has clinically responded to IV therapy, it is reasonable to de-escalate to oral therapy (table 3), unless the patient has another indication for prolonged IV therapy (eg, septic arthritis, prosthetic joint infection, osteomyelitis). Management of such infections are discussed in detail elsewhere. (See "Septic arthritis in adults", section on 'Treatment' and "Prosthetic joint infection: Treatment", section on 'Antibiotic therapy' and "Nonvertebral osteomyelitis in adults: Treatment", section on 'Antibiotic therapy'.)

Duration of treatment — The regimen should be tailored to culture and susceptibility data, once available. However, because anaerobic organisms can be difficult to grow in culture, we continue anaerobic coverage for the full course of therapy even if anaerobic bacteria did not grow on culture.

The total duration of therapy is based on severity of infection and the patient’s clinical response. In general, antibiotic therapy should be continued at least one to two days after symptoms and signs have resolved, which is typically less than seven days.

Most infections require no more than 14 days of therapy, but deep or complicated infections may require longer durations, particularly if a joint or bone is involved [1]. (See "Infectious tenosynovitis" and "Septic arthritis in adults" and "Nonvertebral osteomyelitis in adults: Treatment".)

Spectrum of antibiotic coverage — The spectrum of antibiotics for animal bites are based on the pathogens most frequently isolated from infected wounds [27,35,36]. Scarce data are available to support specific antibiotic regimens for animal bites; our suggestions are based on our clinical experience and generally agree with those of expert guidelines [1,22].

The most definitive data are derived from a study of 50 infected dog bites and 57 infected cat bites that were cultured from 18 university-affiliated emergency departments in the United States in 1994 and 1995 [27]. In this study, the average infected bite wound culture yielded five separate bacterial isolates, and mixed aerobic and anaerobic bacteria were present in the majority of infections.

Antibiotic selection targets the most likely pathogens from human skin flora as well as the oral flora of the biting animal:

●Human skin flora – Pathogens that originate from human skin include Staphylococcus aureus (isolated from 10 of 50 [20 percent] infected dog bites and 2 of 57 [4 percent] infected cat bites) and group A Streptococcus (in 12 percent of infected dog bites and 0 percent of infected cat bites) [27].

The frequency of S. aureus infections, including MRSA, in patients with animal bites has not been evaluated since worldwide increases in MRSA prevalence that began in the late 1990s and early 2000s. Although pets can become colonized with MRSA, the most likely source of MRSA in infected bite wounds is the patient’s own skin flora [37,38]. (See "Methicillin-resistant Staphylococcus aureus (MRSA) in adults: Epidemiology", section on 'Epidemiology' and "Methicillin-resistant Staphylococcus aureus infections in children: Epidemiology and clinical spectrum", section on 'Epidemiology and risk factors'.)

●Oral flora in cats and dogs – Important cat and dog oral pathogens that cause acute infection include the following:

•Pasteurella spp – Pasteurella species (mainly P. multocida and P. canis) are the most common organisms isolated from infected dog and cat bites; they are isolated from 50 percent of infected dog bite wounds and 75 percent of infected cat bite wounds (picture 5) [27]. (See "Pasteurella infections".)

Several antibiotics that are commonly used for skin infections lack reliable activity against Pasteurella spp, including penicillinase-resistant penicillins (eg, dicloxacillin, nafcillin, oxacillin), first-generation cephalosporins (eg, cephalexin, cefadroxil, cefazolin), clindamycin, vancomycin, and macrolides (eg, azithromycin).

•Capnocytophaga spp – These bacteria can cause bacteremia and fatal sepsis after animal bites, especially in patients with asplenia, alcohol use disorder, or underlying liver disease (eg, cirrhosis) [39]. The bacteria are present in the oral cavity of over half of dogs and cats, but dog bites are much more likely to cause infection by these bacteria than cat bites. This organism is isolated in less than 10 percent of infected bite wounds [27]. (See "Capnocytophaga".)

•Anaerobes – Anaerobes are present in at least half of infected wounds [27]. Specific isolates include Bacteroides species (primarily species other than B. fragilis), fusobacteria, Porphyromonas species, Prevotella species, Cutibacterium species (formerly Propionibacterium species), and peptostreptococci [27,40].

We do not provide empiric coverage for Bartonella henselae, a pathogen that is more frequently acquired from cat scratches than cat bites. The most common manifestation of infection from B. henselae is cat-scratch disease, although more serious infections can occur. Infections have a delayed onset (incubation period is 7 to 14 days) with a subacute course and are treated with specifically targeted antibiotics after disease onset. (See "Microbiology, epidemiology, clinical manifestations, and diagnosis of cat scratch disease" and "Treatment of cat scratch disease" and "Endocarditis caused by Bartonella".)

Environmental exposures of the wound after the bite can alter antibiotic selection. For example, exposure to natural bodies of water may require coverage of specific organisms, as discussed separately. (See "Soft tissue infections following water exposure".)

Debridement and surgical consultation — Debridement is required for infected wounds that contain devitalized tissue or retained foreign material (including sutures from prior repairs). All abscesses should be drained. (See "Basic principles of wound management", section on 'Wound debridement' and "Techniques for skin abscess drainage".)

Debridement can often be performed at the bedside. However, we obtain urgent surgical consultation for any of the following (algorithm 1):

●Concern for necrotizing soft tissue infection (eg, rapidly progressive infection, crepitus)

●Deep-space infection (eg, deep abscess, septic arthritis, osteomyelitis, pyomyositis)

●Hand flexor tenosynovitis

●Purulent facial infection with concern for cosmetic deformity

●Persistent signs and symptoms of infection despite appropriate antibiotic therapy

●Non-infectious complications requiring surgery, as outlined below (see 'Indications for surgical consultation' below)

At the time of debridement or surgery, deep tissue samples should be obtained for culture, as described above. (See 'Cultures (wound, blood)' above.)

In general, infected wounds should be left open following debridement. Delayed primary closure may be appropriate for facial wounds, large lacerations, and disfiguring wounds, as described below. (See 'Wound closure' below.)

Uninfected dog and cat bites — In a patient with no symptoms or signs of wound infection, management includes wound care and assessment for antibiotic, tetanus, and rabies prophylaxis [22,34].

Antibiotic prophylaxis

Indications for prophylaxis — Antibiotic prophylaxis is typically provided to patients whose wounds have an increased risk of infection, in agreement with expert guidelines [1].

We suggest post-exposure antibiotic prophylaxis in patients whose wounds have any of the following features (algorithm 1) [1,22-26,41-43]:

●Deep tissue involvement (ie, penetration of the dermis) or crush injury

●Puncture wound (especially cat bites, which tend to leave small but deep wounds)

●Need for surgical repair or debridement

●Closure by primary intention (ie, the wound is sutured closed) or planned delayed primary closure, as discussed below (see 'Wound closure' below)

●Located on the hand, face, or genitals

●Near a bone, joint (including prosthetic joints), or vascular graft

●Located in areas of prior cellulitis or underlying venous and/or lymphatic compromise

●Immunocompromised patient (eg, diabetes, asplenia), liver disease (eg, cirrhosis), or alcohol use disorder

●Bites that have not received any wound care for more than eight hours. Most wounds that do not develop signs of infection by three days and have no retained foreign body will likely not become infected [41,42,44].

Prophylactic antibiotic administration may prevent infection of both dog and cat bite wounds, although the benefit is likely marginal unless one of the above factors are present. A meta-analysis (eight trials, 629 patients) found that patients with dog bite wounds who received prophylactic antibiotics were less likely to develop an infection (10 versus 16 percent, relative risk 0.56, 95% CI 0.38-0.82) [25]. A subsequent meta-analysis (seven trials, 463 patients with dog bites) found that prophylactic antibiotics were associated with a decreased rate of infection, but the results did not reach statistical significance (4 versus 6 percent, odds ratio 0.74, 95% CI 0.3-1.85) [26]. A small trial of 11 patients with cat bites found that no patients who received oxacillin prophylaxis developed an infection compared with four of six patients who received placebo [45].

The benefit of prophylactic antibiotics in reducing infection appears greatest in selected patients, such as those with bites on the hand. In the three included trials in the above meta-analysis with dog bites to the hand (104 patients), patients who received prophylactic antibiotics were less likely to develop an infection (2 versus 28 percent, odds ratio 0.1, 95% CI 0.01-0.86) [26]. Evidence for prophylactic antibiotics in bite wounds undergoing primary closure is mixed and limited by varied preparation and closure protocols and location and nature of the wounds. Some studies have found similar rates of infection (approximately 6 to 8 percent) regardless of prophylactic antibiotic use [44,46-48], while other studies have found lower infection rates (≤2 percent) with prophylactic antibiotics [49-51]. Use of antibiotic prophylaxis is also based upon indirect evidence for a higher risk of wound infection in patients with poor circulation and immunocompromise.

Prophylactic antibiotic regimens — We prefer amoxicillin-clavulanate (875/125 mg every 12 hours in adults) for dog and cat bite prophylaxis. The first dose should be administered as soon as possible after the bite.

Antibiotic options for prophylaxis are the same as for treatment of infection, but the duration of prophylaxis is only three to five days (table 3) [1]. (See 'Oral regimens' above.)

For bites from mammals other than cats and dogs or bites exposed to unique environments, prophylaxis against additional pathogens may be indicated, as discussed elsewhere. (See 'Bites from mammals other than dogs and cats' below and 'Spectrum of antibiotic coverage' above.)

Wound management — This involves wound exploration and closure, if appropriate, or surgical consultation in certain circumstances. Initial wound preparation is discussed above. (See 'Wound preparation' above.)

Indications for surgical consultation — Most dog and cat bites can be managed without surgical consultation. For uninfected bites, we advise urgent surgical consultation in the following circumstances (algorithm 1) [52]:

●Complex facial laceration

●Deep wound near bone, tendon, joint, or other major structure

●Wound associated with neurovascular compromise

●Retained foreign body that cannot be removed at the bedside

Wound closure — For most patients with uninfected bite wounds, we suggest that the wounds be left open to heal by secondary intention rather than by primary closure (algorithm 1 and figure 2). (See "Minor wound evaluation and preparation for closure", section on 'Type of closure'.)

Primary closure is a reasonable alternative in a patient with a facial laceration (including a cat bite) that is sufficiently large to affect cosmesis or a gaping dog bite on the trunk, arm, or leg (not on a hand or foot) who meets all of the following criteria:

●Uninfected wound

●Immunocompetent patient

●Recent bite (<12 hours old for bites on an extremity, <24 hours old for facial bites)

●No crush injury or puncture wound

●No prior episode of cellulitis or venous/lymphatic compromise on the affected extremity

For a wound that may benefit from primary closure but has one of these contraindications, the patient may be started on prophylactic antibiotics with a plan for delayed primary closure after three to four days. Unless the clinician has extensive experience with delayed primary closure, referral to a surgeon or other wound expert is advised since additional debridement (eg, of excessive accumulated granulation tissue) may be necessary at the time of closure. (See "Minor wound evaluation and preparation for closure", section on 'Delayed primary closure'.)

The choice of bite wound closure (ie, primary closure, healing by secondary intention, or delayed primary closure) should be individualized to the nature of the wound, whether irrigation and debridement can reasonably clean the wound, and the immune status of the host. Primary closure hastens healing and reduces adverse cosmetic outcomes [1,22,44,52-55]. However, for small wounds and puncture wounds, the potentially increased risk of infection from primary closure typically outweighs the minimal cosmetic benefit [24]. Facial wounds are an exception given increased cosmetic consequences and a lower rate of infection compared with other anatomic sites [1,44,49-51]. The waiting period during delayed primary closure permits the host defense system to decrease bacterial load and to ensure that no infection develops, which is a contraindication to closure.

We agree with the Infectious Diseases Society of American (IDSA) guidelines for most cases (eg, against primary closure of non-facial cat bites) [1]. However, even though the IDSA recommends against primary closure of non-facial dog bites, we agree with other experts who favor primary closure of lacerations due to dog bites on the trunk, arms, or legs (though not on the hands or feet) [46,47]. Studies have found that primary wound closure does not increase the risk of infection in such bites but is associated with improved cosmetic outcomes [44,46,47]. However, primary closure of hand wounds, puncture wounds, or wounds with delayed presentations (eg, >8 hours since injury) is associated with an increased rate of infection [24,44,46].

The following summarizes our approach for each closure type:

●Secondary intention – Wounds left open to heal by secondary intention should undergo debridement of devitalized tissue, exploration for retained foreign material, copious irrigation, and have a dressing applied. (See "Minor wound evaluation and preparation for closure", section on 'Preparation for closure'.)

●Primary closure – Wounds that are primarily closed should be clean following meticulous debridement and copious irrigation. We generally place non-absorbing sutures in the skin and avoid placing subcutaneous sutures because foreign material increases the risk of infection [22]. For facial wounds, we approximate the edges similar to routine wound closure; for large non-facial dog bites, we often loosely approximate the edges to allow for spontaneous drainage. We do not close bite wounds with tissue adhesive. (See "Skin laceration repair with sutures" and "Assessment and management of facial lacerations".)

We administer antibiotic prophylaxis for all patients who undergo primary closure. (See 'Indications for prophylaxis' above.)

Bites from mammals other than dogs and cats — In general, bites by mammals other than dogs and cats should be treated in the same fashion as cat bites [56].

However, some mammalian species can carry specific high-risk oral pathogens that may require additional considerations, including the following [36,56-60]:

●Mice and rat bites may necessitate penicillin or ceftriaxone to cover rat bite fever, which is caused by Spirillum minus, Streptobacillus moniliformis, and Streptobacillus notomytis. (See "Rat bite fever".)

●Rabbit bites may need a fluroquinolone or doxycycline added to the patient’s antibiotic regimen to cover tularemia (caused by Francisella tularensis), although tularemia is more commonly transmitted by routes other than bites. (See "Tularemia: Microbiology, epidemiology, and pathogenesis" and "Tularemia: Clinical manifestations, diagnosis, treatment, and prevention".)

●Monkey bites can transmit B virus, which can cause fatal encephalomyelitis in humans. Antiviral prophylaxis may be indicated in addition to antibacterials. (See "B virus infection".)

FOLLOW-UP CARE — All patients with mammalian bites require close follow-up. We examine all wounds two to three days after initial presentation, regardless of infection status, type of closure, or whether a drain was placed. We instruct the patient (or caregivers) to be evaluated sooner if they are concerned that signs or symptoms of infection are developing or worsening (if already present). Afterwards, the frequency of follow-up is individualized based on extent of healing and need for drain change or suture removal (if indicated). Some experts will evaluate infected wounds daily until significant clinical improvement has been documented, but this may be onerous for the patient and unnecessary in a patient (or caregivers) who can reliably monitor the wound.

Signs of developing or worsening infection on follow-up examination should prompt further wound evaluation (with radiographic imaging and/or surgical consultation, if indicated), suture removal (if present), review of antibiotic regimen and culture results, and/or a switch to intravenous therapy.

Children who have suffered dog bites may require additional follow-up care if they develop symptoms of post-traumatic stress disorder [61]. (See "Posttraumatic stress disorder in children and adolescents: Epidemiology, clinical features, assessment, and diagnosis".)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Skin and soft tissue infections" and "Society guideline links: Rabies" and "Society guideline links: Dog and cat bites".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or email these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Beyond the Basics topics (see "Patient education: Animal and human bites (Beyond the Basics)" and "Patient education: Rabies (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

●Initial evaluation

•Wound preparation – Initial wound care helps to prevent infection and facilitates examination; it includes applying direct pressure to control any bleeding, cleansing the wound with soap and water or an antiseptic solution, removing any visible debris, and irrigating with tap water or sterile saline (algorithm 1). (See 'Wound preparation' above.)

•Physical examination – Examine the wound for proximity to important structures (eg, joints, tendon, bone), depth, foreign material, cosmetic implications, neurovascular status distal to the wound, and signs of infection. Wound proximity to a joint may not be apparent without testing full range of motion (algorithm 1). (See 'Physical examination' above.)

Infections, if present, include cellulitis, abscess, tenosynovitis, or deep space infection (eg, rapidly progressive pain, crepitus, progression despite initial antibiotics, fever, or other systemic manifestations). (See 'Assessing for infection' above.)

•Role of cultures and imaging – Wound cultures should be obtained from infected wounds. For infected wounds, deep bites, and all cat bites, we obtain radiographs to evaluate for a foreign body or bone involvement. Imaging is not necessary for most superficial dog bites and clinically uninfected wounds (algorithm 1). (See 'Ancillary tests' above.)

●Management

•Rabies and tetanus prophylaxis – Animal bites can transmit rabies and tetanus, which are potentially fatal diseases. Administration of appropriate prophylaxis is essential. (See 'Rabies and tetanus post-exposure prophylaxis' above.)

-Indication for rabies prophylaxis depends on the type of animal bite and wound (algorithm 2). All patients with an indication for rabies prophylaxis should receive a rabies vaccine series, and most will require rabies immune globulin (table 1 and algorithm 1).

-For a patient fully vaccinated against tetanus, we administer a tetanus toxoid-containing vaccine only if their last dose was given ≥5 years ago (or if the date of their most recent vaccine is uncertain).  Options include diphtheria-tetanus toxoid (Td) or diphtheria toxoid-tetanus toxoid-acellular pertussis vaccine (Tdap). For unvaccinated or partially vaccinated patients, we administer a tetanus toxoid-containing vaccine and tetanus immune globulin (table 2 and algorithm 1).

•Infected bites – Most patients with infected bites can be managed as outpatients with oral antibiotics. For oral therapy, we suggest treatment with amoxicillin-clavulanate (875/125 mg orally every 12 hours in adults; see table for pediatric dosing) for 5 to 14 days (Grade 2C). (See 'Oral regimens' above.)

Intravenous (IV) antibiotics are preferred in certain circumstances, such as deep space infection, systemic illness, rapidly progressive erythema, progression after 48 hours of oral antibiotics, or proximity of the lesion to an indwelling device (eg, prosthetic joint or vascular graft). Our preferred intravenous option is ampicillin-sulbactam (3 g intravenously every six hours). Other options are listed in the tables (table 3 and table 6). (See 'Choosing oral versus IV therapy' above and 'Intravenous regimens' above.)

The duration of antibiotic therapy is based on severity of infection and the patient's response. Our preferred regimens cover the organisms most frequently isolated from infected dog and cat bites and are well tolerated in most patients. Most patients do not require empiric coverage for MRSA. (See 'Duration of treatment' above and 'Spectrum of antibiotic coverage' above.)

Debridement of devitalized tissue, removal of foreign material, and drainage of abscess should be performed (algorithm 1). Wounds should be left open to heal by secondary intention. In some cases, urgent surgical consultation is appropriate, as described below. (See 'Debridement and surgical consultation' above.)

•Uninfected bite wounds – For patients with any of the following risk factors for infection, we suggest three to five days of post-exposure antibiotic prophylaxis with amoxicillin-clavulanate (875/125 mg orally every 12 hours in adults; see table for pediatric dosing) (table 3 and algorithm 1) (Grade 2C). (See 'Antibiotic prophylaxis' above.)

-Deep tissue involvement, crush injury, or puncture wound (especially cat bites)

-Need for surgical repair or debridement

-Closure by primary intention or planned delayed primary closure

-Located on the hand, face, genitals, or near a bone, joint, vascular graft, or area of prior cellulitis or venous and/or lymphatic compromise

-Immunocompromised patient

-Bites that have not received any wound care for more than eight hours

For most patients, we suggest that bite wounds be left open to heal by secondary intention rather than primary closure (algorithm 1) (Grade 2C). Primary closure increases risk of infection and does not significantly improve cosmetic outcomes for most patients.

Primary closure is a reasonable alternative for a patient with a facial laceration (including a cat bite) that is sufficiently large to affect cosmesis or a gaping dog bite on the trunk, arm, or leg (not on a hand or foot) who meets all of the following criteria (see 'Wound closure' above):

-Uninfected wound

-Immunocompetent patient

-Recent bite (<12 hours old for bites on an extremity, <24 hours old for facial bites)

-No crush injury or puncture wound

-No prior episode of cellulitis or venous/lymphatic compromise on the affected extremity

Primary closure is not appropriate for patients who don’t meet these criteria.

•Indications for surgical consultation – Urgent surgical consultation​​ is warranted in certain situations (algorithm 1) (see 'Debridement and surgical consultation' above and 'Indications for surgical consultation' above): 

-Complex facial lacerations 

-Deep wounds close to bone, tendons, joints, or other major structures 

-Neurovascular compromise 

-Retained foreign material not amenable to removal at the bedside

-Deep-space or necrotizing soft tissue infections (eg, hand flexor tenosynovitis, necrotizing fasciitis, septic arthritis), purulent facial infection with concern for cosmetic deformity, or infections not improving with intravenous antibiotics

•Follow-up care – All patients with animal bites require follow-up examinations, typically within two to three days. (See 'Follow-up care' above.)