Mammal bites

8 Interesting Facts of Mammal bites

  1. Mammal bites injuries can range in severity from minor superficial contusions, abrasions, or lacerations to severe crushing or tearing injuries with damage to deep structures
  2. Type and degree of injury reflect tooth anatomy and jaw strength of biting animal, ferocity of attack, and anatomic location of injury
  3. Evaluation includes determining species of animal involved, circumstances of bite, health and vaccination status of animal (if known) and patient, and whether animal is available for observation
  4. Wound management consists of bleeding control, cleaning, irrigation, exploration for foreign body or injury to deep structures, and debridement
  5. Primary wound closure can be considered in select bite wounds (primarily facial bites) but is contraindicated in wounds at high risk of infection
  6. Antimicrobial prophylaxis is recommended for 3 to 5 days in certain high-risk bites (eg, cat, human), anatomic locations (eg, hand), and high-risk patients; amoxicillin–clavulanic acid is usually the first line agent 
  7. Administer tetanus and rabies vaccinations if warranted by history and circumstances
  8. Overall rate of infection after mammal bites is 10% to 20%; cat and human bites carry highest risk of infection 

Pitfalls

  • A bite reported to be from another child or a pet may actually be a bite or other injury inflicted by an adult in cases of child abuse 
    • Other injuries associated with child abuse or evidence of past injuries on radiography may be present, and an intercanine distance greater than 3 cm (suggesting an adult human bite) may be found on examination
  • In adults, consider bites with lacerations on a clenched fist to possibly be human, even if history provided is inconsistent
  • Mammal bites are lacerations, punctures, abrasions, avulsions, contusions, or other wounds of varying severity, caused by teeth of a mammal (eg, canine, feline, rodent, human)
  • Type and degree of injury reflect tooth anatomy and jaw strength of biting animal, ferocity of attack, and anatomic location of injury

Classification

  • No universal classification; published classification schemes have been based on degree of involvement of underlying structures and presence of vascular or peripheral nerve injury 
    • Bite wound severity
      • Grade 1
        • Superficial skin lesion
        • Torn skin
        • Scratched skin
        • Bite canal (hole in skin)
        • Crushing injury
      • Grade 2
        • Wound extending from skin to fascia, muscle, or cartilage
      • Grade 3
        • Wound with tissue necrosis or tissue loss
    • Severity of open dog bite wounds on the face
      • Grade 1
        • Superficial injury
      • Grade 2
        • Deep injury involving muscle
      • Grade 3
        • Deep injury involving muscle with loss of tissue
      • Grade 4
        • Deep injury involving muscle with loss of tissue and injury to vessels or nerves
      • Grade 5
        • Deep injury involving muscle with loss of tissue, injury to vessels or nerves, and bone involvement
  • Risk of bite wound infection 
    • Low risk
      • Species: dog (except hand), rodent
      • Location: face, scalp, mucosa
      • Wound type: large, superficial, clean, recent
    • High risk
      • Species: cat, human, primate, pig, camel
      • Location: hand, over joint or tendon, through and through oral, below knee
      • Wound type: puncture, extensive tissue damage, contaminated or devitalized tissue, old or sutured
      • Patients at especially high risk include those who are immunosuppressed or elderly; those who have diabetes, prosthetic heart valve, peripheral vascular disease, or cirrhosis; and those who abuse alcohol

Clinical Presentation of Mammal Bites

History

  • Type and degree of injury reflects the anatomy of the teeth and jaw strength of the biting animal, the ferocity of the attack, and anatomic location of injury
    • Most animal bite wounds are on hands, arms, or legs (70%-80% of dog bites) 
      • Head, nape of neck, or anterior neck are involved in 10% to 30% of cases (particularly in children) 
        • Up to 90% of dog bite wounds in children aged younger than 5 years involve face and anterior aspect of neck 
    • Most human bite wounds are on fingers, hands, or arms 
      • May be direct (by occlusion of biter’s teeth on patient) or indirect (eg, clenched fist injury resulting from patient striking another person in teeth with closed fist) 
      • 10% to 20% of bites occur on breasts and genitals 
  • In all cases, determine the following: 
    • Species of animal involved
    • Circumstances of bite (eg, provoking factors)
    • Health and vaccination status of animal and patient
  • Acute presentation (within hours of the incident)
    • Spectrum of injury includes: 
      • Superficial abrasions
      • Lacerations
      • Puncture wounds
      • Contusions or crush wounds
      • Degloving injuries with major soft tissue loss
      • Perforating injuries extending to, or including, underlying bone or internal organs
    • May be associated with head injury or shock due to hemorrhage
  • Delayed presentation (usually more than 12 hours after incident) with developing infection
    • Typically minor wound for which medical attention was not initially sought
    • Likelihood of infection and rapidity of onset vary according to animal species, nature and site of bite wound, and individual patient susceptibility 
    • Signs or symptoms of localized infection include: 
      • Swelling
      • Pain and tenderness
      • Erythema
      • Wound exudate
    • Systemic infection is uncommon; if this occurs, symptoms may include: 
      • Fever or chills
      • Myalgia
      • Lymphadenopathy
      • Malaise
      • Nausea or vomiting

Physical examination

  • Acute presentation (within hours of the incident)
    • Examination findings vary according to animal involved, ferocity of the bite, and anatomic location
    • Document wound type and measurements 
    • Explore seemingly minor injuries to assess for foreign bodies and penetration into bone or joints 
      • Minor injury may be characterized by: 
        • Superficial abrasions or tears
        • Contusions
        • Puncture wounds
        • May be accompanied by bruising and swelling
    • Assess motor and sensory nerve and vascular function 
    • More severe injuries include: 
      • Laceration or avulsion
      • Severe crush wounds
      • Degloving injuries with major soft tissue loss
      • Perforating injuries extending to, or including, underlying bone or internal organs
      • May have evidence of vascular or neurologic compromise
      • May present with life-threatening hemodynamic compromise or associated head injury (particularly in children)
  • Delayed presentation with infection (usually more than 12 hours after the incident)
    • Likelihood of infection and infecting organisms vary according to animal species, nature and site of bite wound, and individual patient susceptibility 
    • Signs of localized (rarely, systemic) infection include: 
      • Swelling
      • Tenderness
      • Erythema
      • Wound exudate
      • Abscess
      • Lymphadenopathy
      • Fever
    • Typically, patient has minor wounds not requiring immediate medical attention

Causes and Risk Factors of Mammal Bites

Causes

  • Most common causes of mammal bite injury in the United States
    • Dogs (most common cause of animal bite injury, representing 85%-90% of animal bites) 
    • Cats (5%-15% of cases) 
    • Rodents (up to 7% of cases) 
    • Humans (2%-3% of cases) 
  • Bites from other species are less common (less than 2% of all mammal bites) in the United States, but may be more frequent in other countries: 
    • Bats
    • Monkeys
    • Ferrets
    • Raccoons
    • Foxes
    • Livestock (eg, cows, horses, pigs, camels)
    • Minks
    • Apes

Risk factors and/or associations

Age
  • Higher incidence of dog bites in children younger than 5 years 
Sex
  • Dog bites are more common in males by a ratio of 2 to 1 
  • Cat bites are more common in females by a ratio of 2 to 1 
Other risk factors/associations
  • Pet ownership or residence in a home with pets, especially dogs 
    • In 66% to 90% of dog bites, the dog is owned by the patient or known to the patient 
  • Working with laboratory animals (eg, rodents, monkeys), livestock, or wildlife 

How are Mammal Bites diagnosed

Primary diagnostic tools

  • Base diagnosis on history and physical examination
    • Determine species of animal involved, circumstances of bite, health and vaccination status of animal (if known), and whether animal is available for observation 
    • Determine patient vaccination status and presence of risk factors for infection 
  • Obtain laboratory tests (eg, wound culture) if infection is suspected 
  • Obtain plain radiographs of all clenched fist human bite injuries, puncture wounds near bone or joint, or penetrating scalp injuries; obtain CT if there is a possible head injury, particularly in small children 
    • In other cases, radiography or CT is indicated only if there is an associated fracture or a foreign body is suspected (eg, teeth in wound) 
  • Obtain ultrasonography if fluid collection or abscess is suspected in soft tissue 
  • Bite reported to be from a child or a pet may actually be a bite or other injury inflicted by an adult in cases of child abuse 
    • Other injuries associated with child abuse or evidence of past injuries on radiography also may be present, and an intercanine distance greater than 3 cm (suggesting an adult human bite) may be found on examination
  • CBC with differential 
    • Not routinely obtained
    • Indicated in suspected bacterial infection
    • WBC count is elevated during infection
  • C-reactive protein level and/or erythrocyte sedimentation rate 
    • Not routinely obtained
    • Indicated in suspected bacterial infection
    • Elevated values suggest infection
  • Wound culture 
    • Not routinely obtained
    • Indicated for clinically infected bite wounds 
    • Obtain swabs for Gram staining and aerobic and anaerobic cultures
  • HIV serology
    • Indicated as baseline after bite from human who has or may have HIV infection 
  • Hepatitis serology
    • Indicated as baseline after bite from human who has or may have a hepatitis infection 
  • Plain radiography
    • Indicated for:
      • Clenched fist injuries 
      • Puncture wounds near bone or joint 
      • Penetrating scalp injuries 
      • Possibility of any bone injury 
      • Possibility of a foreign body (eg, teeth in wound) 
  • CT
    • Indicated when there is a possible head injury, especially in infants and children younger than 2 years who sustain substantial bite wounds to scalp 
  • Ultrasonography
    • Indicated if fluid collection or abscess is suspected in soft tissue 

Differential Diagnosis of Mammal Bites

Most common

  • Assault (eg, in patient found unconscious with no witnesses to an animal attack)
    • Trauma is due to an attack by another human without biting
    • May present with lacerations, punctures, abrasions, avulsions, contusions, or other wounds of varying severity
    • Unlike in animal bites, no teeth marks are present
    • Diagnosis may be determined on basis of particular characteristics of wounds from sharp or blunt instruments, punches, kicks, or weapons (eg, firearms) that can be discerned by specialists in forensic medicine or trauma

How are Mammal Bites treated

Goals 

  • Achieve hemostasis
  • Promote tissue healing
  • Prevent infection

Disposition

Admission criteria

  • Patients with any of the following:
    • Multiple and/or severe injuries 
    • Wound requires surgical intervention (eg, debridement, drainage, reconstruction) 
    • Significant bite to the hand or cranium 
      • Delayed presentation
      • Significant tissue damage
    • Human bite with puncture wound 
    • High risk of infection due to animal, wound type, or patient characteristics, for example: 
      • Cat, human, primate, pig, or camel bite
      • Wound on hand, over joint or superficial tendon, through oral cavity, or below knee
      • Puncture wound
      • Extensive tissue damage
      • Contaminated or devitalized tissue
      • Delayed presentation (more than 24 hours after bite) or wound has been sutured
      • Immunocompromised state (eg, HIV, chemotherapy, organ transplant)
      • Prosthetic heart valve
      • Advanced age
      • History of alcohol abuse or cirrhosis
      • Peripheral vascular disease
      • Diabetes
    • Cellulitis that is severe, rapidly spreading, or advanced past 1 joint 
    • Systemic signs of infection 
    • Infection refractory to oral antibiotic therapy 
    • Social or compliance issues 

Recommendations for specialist referral

  • Refer patients with severe bite injuries requiring extensive debridement or reconstruction to a general, hand, orthopedic, or plastic surgeon according to location and nature of injury 
  • Report dog bites to local law enforcement authorities according to state regulations

Treatment Options

Wound management consists of cleaning, irrigation, exploration for foreign body or injury to deep structures, and debridement 

  • Control active bleeding with direct pressure; if needed, a temporary suture may be placed 
  • Intractable bleeding on an extremity can be controlled with a proximal blood pressure cuff inflated above systolic pressure for 20 minutes 

Primary closure of wounds is controversial 

  • Avoid suturing wounds at high risk of infection, such as: 
    • Puncture or crush injuries
    • Wounds more than 24 hours old
    • Bite wounds over hands, feet, and joints
    • Cat or human bites (except on face or scalp) 
    • Bite wounds in immunocompromised patients
  • 2 to 3 days after injury, reevaluate wounds left open and manage by delayed primary closure or allow to heal by secondary intention
  • Consider suturing selected bite wounds when cosmesis is an issue; determine on a case-by-case basis 
    • There is general consensus that facial and scalp bite wounds from any mammal should be sutured if less than 6 hours old 
      • There is some evidence that this timeframe can be safely extended to 12 hours or longer, particularly for dog bites 
    • Most other uncomplicated dog bites are safe to suture (except those involving the hand)

Antimicrobial prophylaxis is not universally recommended;  it has not been shown to reduce rate of infection, except in cases of bite wounds on hands 

  • Antimicrobial prophylaxis for 3 to 5 days is generally recommended for: 
    • Bites from any species (including dog or human) involving the hand 
    • All cat, monkey, pig, and camel bites 
    • Bites from any species in high-risk patients, such as those with: 
      • Immunocompromised (eg, HIV, chemotherapy, organ transplant) or asplenic state 
      • Prosthetic heart valve
      • Advanced age
      • History of alcohol abuse or cirrhosis
      • Peripheral vascular disease
      • Diabetes
    • Any bites with delayed presentation 
    • Moderate to severe bites, especially involving hands or face 
    • All bites requiring primary closure 
    • Bites in areas with preexisting or resultant lymphedema 
    • Deep punctures or bites that may have penetrated periosteum or joint capsule 
  • Choice of agent is determined by type of injury
    • Amoxicillin–clavulanic acid is appropriate for bites from most species and involving most anatomic locations 
    • Alternatives include clindamycin, doxycycline, fluoroquinolones (eg, ciprofloxacin, moxifloxacin), or cefuroxime 

Elevate and immobilize the injury for the first 48 to 72 hours 

  • Significant hand wounds may benefit from immobilization in the position of function for 3 to 5 days 

Administer tetanus and rabies prophylaxis if warranted by history and circumstances 

  • Tetanus toxoid is indicated if 10 years or more have passed since last dose and patient has completed a full primary course of immunization 
  • Tetanus
  • Rabies
    • Consists of rabies immunoglobulin infiltrated locally into wound and rabies vaccination at presentation, followed by rabies vaccination on postexposure days 3, 7, and 14 
    • Generally not required for patients with dog, cat, or ferret bites providing animal does not demonstrate signs of rabies 
      • Monitor animal for at least 10 days and immediately initiate postexposure prophylaxis if it develops signs of rabies, becomes sick, or dies 
    • Consider immediate postexposure prophylaxis for patients with bat, raccoon, skunk, fox, or other carnivore bites; if animal is being tested, administration may be delayed until results are available 
    • Not usually required but is determined on an individual basis for other bites 
    • Refer to CDC resources for further information 

Consider postexposure prophylaxis for patients who may have been exposed by human bite to HIV or hepatitis B, or by monkey bite to herpesvirus B 

  • Consult with infectious disease specialist and/or CDC resources 

Treat established infections with an antibiotic active against aerobic and anaerobic bacteria; amoxicillin-clavulanate is the first line agent 

Drug therapy

  • Antimicrobial prophylaxis 
    • Antimicrobial prophylaxis for 3 to 5 days is recommended 
    • First line agent
      • Amoxicillin–clavulanic acid Oral dosage (immediate-release formulations and non-ES suspensions)
        • Amoxicillin Trihydrate, Clavulanate Potassium Oral suspension; Infants 3 months and older, Children, and Adolescents weighing less than 40 kg: 25 to 45 mg/kg/day amoxicillin component PO divided every 12 hours. Max: 875 mg amoxicillin and 125 mg clavulanic acid per dose. 
        • Amoxicillin Trihydrate, Clavulanate Potassium Oral tablet; Adults, Adolescents, and Children weighing 40 kg or more: 875 mg amoxicillin with 125 mg clavulanic acid PO 2 times daily. 
    • Alternatives include clindamycin plus either trimethoprim-sulfamethoxazole (pediatric patients) or a fluoroquinolone (adult patients) 
      • Clindamycin
        • Clindamycin Palmitate Hydrochloride Oral solution; Neonates, Infants, Children, and Adolescents: 10 to 25 mg/kg/day PO divided every 6 to 8 hours (Max: 900 mg/day) in addition to trimethoprim-sulfamethoxazole. 
        • Clindamycin Hydrochloride Oral capsule; Adults: 300 mg PO 3 times daily in addition to a fluoroquinolone. 
      • Sulfamethoxazole-trimethoprim
        • Sulfamethoxazole, Trimethoprim Oral suspension; Infants older than 2 months, Children, and Adolescents: 4 to 6 mg/kg (trimethoprim component) PO every 12 hours (Max: 160 mg trimethoprim per dose) plus clindamycin. 
      • Ciprofloxacin
        • Ciprofloxacin Hydrochloride Oral tablet; Adults: 500 to 750 mg PO every 12 hours in addition to clindamycin. 
  • Established infection 
    • Duration of antibiotic therapy is generally 7 to 14 days until infection has resolved
    • Monotherapy
      • Amoxicillin–clavulanic acid
        • Amoxicillin Trihydrate, Clavulanate Potassium Oral suspension; Infants 3 months and older, Children, and Adolescents weighing less than 40 kg: 25 to 45 mg/kg/day amoxicillin component PO divided every 12 hours. Max: 875 mg amoxicillin and 125 mg clavulanic acid per dose.
        • Amoxicillin Trihydrate, Clavulanate Potassium Oral tablet; Adults, Adolescents, and Children weighing 40 kg or more: 875 mg amoxicillin with 125 mg clavulanic acid PO 2 times daily. 
      • Ampicillin-sulbactam
        • Ampicillin Sodium, Sulbactam Sodium Solution for injection; Infants: 100 to 200 mg/kg/day ampicillin component IV in divided doses every 6 hours.
        • Ampicillin Sodium, Sulbactam Sodium Solution for injection; Children and Adolescents less than 40 kg: 300 mg/kg/day ampicillin component IV in divided doses every 6 hours.
        • Ampicillin Sodium, Sulbactam Sodium Solution for injection; Adults: 1.5 g (1 g ampicillin and 0.5 g sulbactam) or 3 g (2 g ampicillin and 1 g sulbactam) IV every 6 hours.
      • Doxycycline
        • Doxycycline is not typically used in children younger than 8 years
        • Oral dosage
          • Doxycycline Hyclate Oral tablet; Adults, Adolescents, and Children 8 years and older and weighing 45 kg or more: 100 mg PO every 12 hours. 
          • Doxycycline Hyclate Oral tablet; Children 8 years and older and Adolescents weighing less than 45 kg: 2 mg/kg/dose PO every 12 hours. Max: 100 mg/dose.
        • Intravenous infusion dosage
          • Doxycycline Hyclate Solution for injection; Children 8 years and older and Adolescents weighing less than 45 kg: 4.4 mg/kg IV on day 1, then 2.2 to 4.4 mg/kg/day as 1 or 2 doses. Max: 200 mg/day.
          • Doxycycline Hyclate Solution for injection; Adults, Adolescents, and Children 8 years and older and weighing 45 kg or more: 100 mg IV every 12 hours. 
      • Moxifloxacin
        • Moxifloxacin Hydrochloride Solution for injection; Adults 18 years and older: 400 mg PO or IV every 24 hours. 
        • Safe and effective use of systemic moxifloxacin dosage forms has not been established in neonates, infants, children, and adolescents younger than 18 years
    • Combination therapy (metronidazole plus a cephalosporin)
      • Cefuroxime
        • Cefuroxime Sodium Solution for injection; Infants 3 months and older, Children, and Adolescents: 50 to 100 mg/kg/day IV in divided doses every 6 to 8 hours (Max: 2.25 g/day).
        • Cefuroxime Sodium Solution for injection; Adults: 750 mg IV every 8 hours.
      • Ceftriaxone
        • Ceftriaxone Sodium Solution for injection; Infants, Children, and Adolescents: FDA-approved labeling is 50 to 75 mg/kg/day IV/IM divided every 12 to 24 hours. Max: 2 g/day.
        • Ceftriaxone Sodium Solution for injection; Adults: 1 g IV every 12 hours. 
      • Metronidazole
        • Metronidazole Solution for injection; Infants and Children: 30 mg/kg/day IV in divided doses every 8 hours (Max: 4 g/day) plus a cephalosporin.
        • Metronidazole Solution for injection; Adults and Adolescents: 500 mg IV every 8 hours plus a cephalosporin. 

Nondrug and supportive care

Wound management

  • Cleanse with soap and water immediately; use fine pore sponge 
  • Irrigate with copious quantities of normal saline, water, or dilute povidone-iodine solution to remove all visible dirt and foreign material 
  • Remove any foreign bodies that irrigation does not remove (eg, dirt, debris, teeth) 
  • Explore wound for bone or tendon involvement 
  • Conservatively debride devitalized tissue 

Comorbidities

  • Patients with any of the following always require prophylactic antimicrobial therapy after any mammal bite: 
    • Immunosuppressed state
    • HIV infection
    • Recent transplant
    • Corticosteroid therapy
    • Diabetes
    • Cancer chemotherapy
    • Prosthetic valve
    • Peripheral vascular disease
    • Advanced age
    • History of alcohol abuse
    • Cirrhosis
    • Social and compliance issues

Monitoring

  • Provide follow-up at 24 to 48 hours to review wound healing and monitor for signs of infection 
  • Every few days for the first 21 days following the bite, examine patients with possible exposure to herpesvirus B from monkey bite for appearance of vesicles on skin 

Complications and Prognosis

Complications

  • Wound infection
    • Infection may be present with delayed presentation (patient presents days to weeks after bite) and tends to develop most quickly following cat bites (within a few days) compared with bites from other mammals (up to several weeks)
    • Most infections are polymicrobial, including both aerobic and anaerobic bacteria
    • Common pathogens include Staphylococcus species, Streptococcus species, Pasteurella multocida (primarily cat bites), Capnocytophaga canimorsus (primarily dog bites), Neisseria species, Corynebacterium species, Moraxella species, Eikenella corrodens (human bites), Fusobacterium species, and Bacteroides species 
    • Rate of infection depends on type of mammal that inflicted the bite and anatomic location as follows: 
      • Cat bites: 30% to 50%
      • Human bites: 15% to 25%
      • Dog bites: 5% to 25%
      • Bites on hand: 18% to 36%
      • Bites on arm: 17% to 20%
      • Bites on leg: 7% to 15%
      • Bites on face: 4% to 11%
    • Organisms of specific importance include: 
      • Capnocytophaga canimorsus
        • Infection associated with dog bites; may give rise to sepsis, meningitis, endocarditis, or septic arthritis in immunocompromised patients
      • Pasteurella multocida
        • Infection associated with cat bites; may lead to abscess, tenosynovitis, joint infections, or osteomyelitis
        • Can seed arthritic joints and prosthetic valves, causing septic arthritis, endocarditis, and osteomyelitis at remote sites
      • Eikenella corrodens
        • Can produce serious, chronic infection after human bites, particularly clenched fist injuries
    • Obtain swab of clinically infected bite wounds for Gram stain and culture; open any sutures, and incise and drain abscess if present 
    • Treat established infections with an antibiotic active against aerobic and anaerobic bacteria; amoxicillin-clavulanate is the first line agent 
  • Systemic infections
    • Animal bites 
      • Lyssavirus species (rabies)
      • Leptospira interrogans (leptospirosis)
      • Bartonella henselae (cat-scratch disease)
      • Herpesvirus simiae (herpesvirus B)
      • Brucella species (brucellosis)
      • Clostridium tetani (tetanus)
      • Francisella tularensis (tularemia)
      • Streptobacillus moniliformis (rat-bite fever)
    • Human bites 
      • HIV-1 or HIV-2
      • HBV or HCV
      • Treponema pallidum (syphilis)

Prognosis

  • Overall prognosis for mammal bites is favorable 
  • Most injuries are superficial and not associated with significant trauma
  • Majority of dog bite fatalities occur in children younger than 10 years, with children younger than 4 years at greatest risk 
  • Adults older than 50 years also have increased fatality rate 

Screening and Prevention

Prevention 

  • Educate parents and children about how to prevent dog bites, such as:
    • Refraining from leaving young children alone with pets
    • Avoiding unfamiliar dogs
    • Not disturbing a dog it is eating, sleeping, or caring for puppies
    • Interacting with their own dog and what to do if approached by a strange dog
  • Educate dog owners regarding:
    • Training
    • Socialization of dogs to children from an early age
    • Neutering
    • Regular veterinary care

Sources

Rothe K et al: Animal and human bite wounds. Dtsch Arztebl Int. 112(25):433-42; quiz 443, 2015 Reference 

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