Animal bites

Bite wounds can result in physical trauma, bacterial infection, virus transmission, and in some cases, envenomation. The general management of bite wounds involves assessment of the wound, acute wound management, and prophylaxis to prevent infections (e.g., rabies postexposure prophylaxis, tetanus prophylaxis, antibiotic prophylaxis). More specific therapy is based on the location of the wound and the animal that inflicted the wound. Depending on the severity and location of the injury, specialist management may be necessary, e.g., ophthalmology for wounds involving the eye or eyelid.

This article focuses on the bites of nonvenomous animals; see “Envenomation” for more specific information on venomous animals.

• Common bacterial pathogens: (from oral flora): Streptococcus spp., Staphylococcus spp., Pasteurella multocida, Haemophilus influenzae, Capnocytophaga canimorsus, Eikenella corrodens, anaerobic bacteria ^[1]
• Tetanus prophylaxis indicated for:
  • All bite wounds occurring ≥ 5 years after the last tetanus immunization
  • All patients with unknown tetanus vaccination status

Primary wound closure is usually inappropriate for hand and foot bite wounds because of the greater risk of infection. ^[3]

Human and animal rabies are notifiable diseases.

Approach

• Begin acute wound management.
• Obtain a focused history on the bite circumstances and immunization history.
• Assess the wound.
• Cleanse bite using wound irrigation and debridement (e.g., with ≥ 1 liter of normal saline). ^[4]
• Choose wound closure based on the risk of infection.
• Determine the need for antibiotics for bite wounds.
• Determine the need for rabies, tetanus, and additional infection prophylaxis.

Follow local public health protocols as mandatory reporting requirements for animal bites vary regionally.

Diagnostics

• X-rays
  • Indications: suspicion of fracture, joint damage, or retained foreign body
  • Findings: fractures, air in the joint space, radiopaque foreign body (e.g., tooth fragment)
• Laboratory studies
  • Nonhuman animal bites: not indicated unless the wound is clinically infected
  • Human bites: HIV, HBV, and HCV testing of both parties
• Wound cultures: : not indicated unless the wound is clinically infected

Wound care

• Wound irrigation and debridement: all bites
• Wound closure for bite wounds: Weigh the risk of infection against the need for cosmesis. ^[3]
  • Low infection risk: Primary wound closure is likely appropriate.
  • High infection risk: Consider secondary wound closure or tertiary wound closure.

Antibiotics for bite wounds

Approach ^[5]

• Prophylaxis
  • Indications
    • Wound: moderate to severe wounds, hand or face wounds, penetration of periosteum or joint
    • Preexisting conditions: immunocompromise, asplenia, advanced liver disease
    • Animal: mammals other than dogs or rodents ^[2]
  • Duration: 3–5 days
  • Route: oral antibiotics
• Treatment
  • Indications: all infected bite wounds
  • Duration: 7–14 days
  • Route ^[6]
    • Mild infection: oral antibiotics
    • Moderate or severe infection: IV antibiotics

Obtain both aerobic and anaerobic cultures to guide the treatment of infected bite wounds. ^[5][6]

Preferred agents ^[1][6][7][8]

• Oral: : amoxicillin/clavulanate ^[2][5]
• IV: ampicillin/sulbactam ^[2][5]

Alternative agents ^[1][6][7][8]

• Oral
  • 2^nd or 3^rd generation cephalosporin (e.g., cefuroxime ) PLUS anaerobic coverage (e.g., clindamycin OR metronidazole ), if required ^[5]
  • Fluoroquinolone (e.g., ciprofloxacin , levofloxacin ) PLUS anaerobic coverage (e.g., clindamycin , metronidazole ) ^[5]
• IV
  • 3^rd generation cephalosporin (e.g., ceftriaxone ) PLUS anaerobic coverage (clindamycin OR metronidazole ) ^[2][5]
  • Fluoroquinolone (e.g., ciprofloxacin , levofloxacin ) PLUS anaerobic coverage (clindamycin , metronidazole ) ^[2][5]
  • Carbapenem (e.g., ertapenem ) ^[2][5]

Additional prophylaxis ^[2]

• All bites: ensure current tetanus prophylaxis
• Domestic carnivores or known wild reservoirs for rabies: rabies risk assessment and possible rabies PEP
• Human bites: HIV PEP and/or hepatitis B PEP
• Monkey bites: B virus PEP

Foxes, skunks, raccoons, and bats are the main reservoir species for rabies in the US, but all mammals are susceptible. ^[9]

Disposition

• Consult a specialist for complicated wounds.
  • Facial wounds or need for multilayer closure: plastic surgery
  • Eye or eyelid: ophthalmology
  • Hand infections or open fractures: orthopedics
  • Deep tissue infections: general surgery
  • Established infections: infectious disease
• Consider hospital admission for:
  • Injuries requiring surgery and/or general anesthesia for wound care
  • Injuries or infections of deep structures (e.g., tendons, joints, bones)
  • Severe infections: cellulitis, lymphangitis, or lymphadenitis
  • Wounds at high risk for infection or failed outpatient antibiotic therapy

Complications of bite wounds ^[2]

• Structural
  • Fracture
  • Tendon injury
  • Muscle injury
  • Joint injury
  • Neurovascular injury
• Infectious
  • Cellulitis
  • Abscess
  • Tenosynovitis
  • Septic arthritis
  • Osteomyelitis
  • Sepsis

Transmissible bacteria

• High risk of polymicrobial infection from oral flora.
• Organisms include Staphylococcus spp., Streptococcus spp., Corynebacterium spp., Fusobacterium spp., and Eikenella corrodens. ^[2]

Clinical features ^[2]

Signs of wound infection are common as there is often a delay before patients seek health care for human bites.

• Clenched-fist injuries (fight bite): dorsum of the hand is injured when it strikes an individual's teeth
  • Small lacerations over the dorsum of 2^nd–5^thMCPs
  • > 50% associated with bone injury
  • Up to 20% associated with tendon injury
• Occlusive bites: semicircular pattern of bruising, abrasions, and/or lacerations
  • Commonly located on upper extremity or breast
  • May indicate sexual violence, intimate partner violence, or child maltreatment
• Intraoral and oral cutaneous injuries: injuries from the patient's own teeth ranging from small buccal mucosa injuries to through-and-through injuries

Maintain a high degree of suspicion for a clenched-fist injury in dorsal hand lacerations as patients may not initially disclose involvement in an altercation. ^[2]

Management ^[2][10][11]

• Follow the general management of bite wounds.
• Consider primary wound closure for uninfected facial wounds < 24 hours old.
• Consider secondary wound closure or tertiary wound closure in all other cases.
• Provide antibiotic prophylaxis for bite wounds.
• Admit patients with infected human bite wounds and initiate IV antibiotics for bite wounds. ^[11]
• Test both parties for HIV, HBV, and HCV.
• Provide HIV PEP and hepatitis B PEP to both parties as indicated.

Human bites carry a high risk of polymicrobial infection by organisms such as Staphylococcus spp., Streptococcus spp., Corynebacterium spp., Fusobacterium spp., and Eikenella corrodens. ^[2]

Consider screening for sexual violence, intimate partner violence, or child maltreatment in at-risk patients with human occlusive bite wounds. ^[2]

Complications

• General complications of bite wounds
• Transmission of human-specific viral pathogens: e.g., HIV, HBV, HCV, HSV ^[2]

Canines include domestic dogs, foxes, coyotes, and wolves.

• Epidemiology ^[12]
  • 85–90% of animal bites
  • Children > adults
• Transmissible bacteria ^[13]
  • Include aerobic and anaerobic organisms that cause polymicrobial infections
  • E.g., Streptococcus spp., Staphylococcus spp., Pasteurella multocida, Neisseria spp., Fusobaterium spp., Haemophilus influenzae, Capnocytophaga canimorsus
• Clinical features ; ^[2]
  • Location
    • Children: often on the head and neck
    • Adults: most commonly on the extremities
  • Injury pattern
    • Varies depending on the size and breed of the dog
    • May include contusions, abrasions, lacerations, puncture wounds, and/or crush injuries
    • May show signs of wound infection
• Management ^[2][10]
  • Follow management of bite wounds.
  • Consider primary wound closure for uninfected wounds not involving the hand or foot.
  • All other wounds: Consider secondary wound closure or tertiary wound closure.
  • Consider rabies PEP for all bites by:
    • Wild canines
    • Symptomatic dogs
    • Asymptomatic dogs that:
      • Are unvaccinated OR have unknown rabies vaccination status
      • AND cannot be observed for a 10 day period
• Complications: See “Complications of bite wounds.”

Although dog bites are the leading cause of rabies transmission worldwide, the risk of contracting rabies from domestic dogs in the US is low. ^[14]

• Epidemiology ^[12]
  • 5–10% of animal bites
  • Cat bites have an infection rate of > 50% ^[2]
• Transmissible bacteria: similar to dog bites; most commonly Pasteurella multocida ^[13]
• Clinical features ^[2][10][15]
  • Location: most common on the hand or fingers
  • Often a single puncture wound
  • May show signs of wound infection early
• Management ^[2][10]
  • Follow the general management of bite wounds.
  • Most wounds: secondary wound closure
  • Primary wound closure is typically only considered for uninfected facial wounds < 24 hours old.
  • Provide antibiotic prophylaxis for bite wounds for all cat bites.
  • Consider rabies PEP for all bites by:
    • Wild cats
    • Symptomatic cats
    • Asymptomatic cats that:
      • Are unvaccinated OR have unknown rabies vaccination status
      • AND cannot be observed for a 10 day period
• Complications: See “Complications of bite wounds.”

Provide antibiotic prophylaxis for bite wounds (e.g., amoxicillin/clavulanate) with coverage for cat-specific flora (e.g., Pasteurella multocida) because of the high infection rate of cat bites.

Rodents include mice, rats, hamsters, guinea pigs, squirrels, and beavers.

• Epidemiology ^[2][15]
  • Most commonly seen in laboratory workers who handle rodents for research and individuals living in conditions susceptible to rat and mouse infestation (e.g., derelict housing, farms)
  • Children > adults
• Transmissible diseases
  • Leptospirosis
  • Lassa fever
  • Tularemia
  • Hantavirus infection
  • Rat-bite fever ^[16]
    • Transmitted by Streptobacillus moniliformis
    • Characterized by fever, rigors, and polyarthralgia
    • Can cause severe organ damage (e.g., hepatosplenomegaly, interstitial pneumonia, endocarditis)
    • Treatment: penicillin G
• Clinical features
  • Commonly located on the face and/or upper extremities
  • Bite wounds are usually small
  • Signs of wound infection (uncommon)
• Management ^[2][10]
  • Follow the general management of bite wounds.
  • Rabies prophylaxis and antibiotic prophylaxis for bite wounds are not routinely required ^[17]
• Complications
  • General complications of bite wounds
  • Transmission of rodent-specific diseases

Rodents are rarely found to have rabies and have not been known to transmit rabies to humans. ^[17]

• Epidemiology: Bats can be found worldwide and are typically encountered in caves and rocky crevices, mines, trees, and occasionally in urban and indoor spaces.
• Transmissible diseases: Bat bites cause ∼ 80% of rabies cases in the US. ^[14]
• Clinical features: typically small, painless bites that are difficult to identify
• Management ^[14]
  • Follow the general management of bite wounds.
  • Use an antiviral agent, e.g., chlorhexidine or povidone-iodine, when performing wound irrigation and debridement. ^[18]
  • Administer rabies post-exposure prophylaxis for all the following: ^[19]
    • Any bat bite or scratch
    • Any direct contact with a bat
    • Unattended child in the same room as a bat
    • Adults in the same room as a bat who may not be able to recall a bite, e.g., intoxicated, deeply sleeping, or have an intellectual disability

Any direct contact with a bat (e.g., touch, bite, or scratch) may transmit rabies. ^[14]

• Epidemiology: rare; in the US, most monkey bites occur in laboratory workers ^[2]
• Transmissible virus: B-virus (by macaque monkeys)
• Clinical features: varies, may include superficial bruising, puncture wounds, or grouped lacerations ^[2]
• Management
  • Follow the general management of bite wounds.
  • Consider primary wound closure for uninfected facial wounds < 24 hours old.
  • Provide antibiotic prophylaxis for bite wounds.
  • Macaque monkey bites
    • Use an antiviral agent (e.g., chlorhexidine or povidone-iodine) when performing wound irrigation and debridement. ^[20]
    • Provide B virus postexposure prophylaxis if the skin integrity is compromised. ^[2]
      • Valacyclovir (off-label) ^[21]
      • Acyclovir (off-label) ^[21]
• Complications
  • General complications of bite wounds.
  • B virus infection

• Examples: great white shark, tiger shark, bull shark
• Epidemiology
  • Despite posing a relatively low public health risk, shark-related injuries often generate disproportionately great public and media attention.
  • Annually, 70–80 unprovoked shark attacks occur worldwide ^[22]
• Management
  • In the rare event of a patient being admitted with shark-related injuries:
    • Prioritize hemorrhage control
    • Clean wounds thoroughly to prevent infection
  • For more information, see “Management of trauma patients.”

Approx. 7% of shark attacks are fatal. ^[23]