Dog and Cat Bites

Dog and cat bites can cause superficial and deep tissue destruction, as well as serious wound infections. Dog bites occur more frequently in men and children and often cause crushing or tearing trauma. Cat bites are more frequent in adult women and result in puncture wounds. Because puncture wounds allow inoculation of bacteria into the deep tissues, cat bites are more frequently associated with infection. The diagnosis is clinical, and cultures should be obtained if the wound appears infected. Management requires fastidious wound care and antibiotics for high-risk or infected wounds.

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Overview

Epidemiology

International data are lacking, but statistics in the United States include:

  • 3–6 million animal bites per year
  • Most cause only minor wounds, but 1 in 5 cases requires medical attention
  • 2.5% require hospitalization
  • Increased frequency in rural areas
Table: Demographics based on animal
Dog bitesCat bites
Approximately 90% of all animal bitesApproximately 10% of all animal bites
Men > womenWomen > men
Children > adultsAdults > children
Less often result from provocationMore often result from provocation

Microbiology

In addition to the risk of contracting the rabies virus from an animal bite, wound infections can be caused by the following organisms:

Table: Common bacteria involved in bite wounds
Dog bitesCat bitesBoth
  • Capnocytophaga canimorsus
  • Eikenella
  • Proteus
  • Klebsiella
  • Haemophilus
  • Enterobacter
  • Moraxella
  • Corynebacterium
  • Neisseria
  • Prevotella
  • Porphyromonas
  • Bartonella henselae
  • Actinomyces
  • Propionibacterium
  • Clostridium
  • Wolinella
  • Peptostreptococcus
  • Staphylococcus
  • Streptococcus
  • Pasteurella multocida
  • Bacteroides
  • Fusobacterium

Risk factors for bite-wound infection

Patient-related factors:

  • Late presentation 
  • Immunosuppression:
    • Diabetes mellitus
    • Chemotherapy
    • HIV
    • Sickle cell disease
    • Asplenia
  • Venous stasis or vascular disease

Bite-related factors:

  • Cat bite (results in deeper bacterial inoculation) 
  • Significant tissue destruction (crush injury)
  • Hand or foot involvement 
  • Location near a joint or prosthetic device

Clinical Presentation

General characteristics

Table: Differences in presentation of dog and cat bites
Dog bitesCat bites
LocationChildren: head, face, neck
Adults: hands, arms
Extremities
Wound typeCrushing and tearingPuncture
ConsequencesDeeper structures are often damaged (tendons, bones, and blood vessels).Inoculates bacteria into the deep tissues
Risk of infectionLess likelyMore likely

Bilateral, ulcerative, nodular wounds on the dorsum of a patient’s hands after sustaining dog bites

Image: “Ulcerative, nodular wounds” by Warren Alpert Brown University School of Medicine, 1125 North Main Street, Providence, RI 02906, USA. License: CC BY 4.0

Important history to elicit

  • Time of occurrence (how long since bite)
  • Circumstances 
  • Type of animal 
  • Status of animal (rabies risk)
  • Fever
  • Patient risk factors for wound infection

Important physical exam findings

  • Wound exploration:
    • Foreign bodies (teeth, clothing)
    • Local tissue destruction 
    • Deep structure injuries
  • Signs of cellulitis or deep tissue infection (more common in cat bites):
    • Erythema
    • Swelling
    • Purulent discharge
    • Warmth  
  • Local and distal assessment: 
    • Vascular injury
    • Neurologic damage
    • Tendon rupture 
    • Bone injuries (skull and cervical spine fractures in infants and young children)
    • Joint space violation

Diagnosis and Management

Diagnosis

The diagnosis of a cat or dog bite is clinical, but the following may be utilized in select cases:

  • Wound cultures:
    • Can be done if wound is infected in order to guide antibiotic therapy
    • Samples from fresh wounds are not valuable.
  • Blood cultures should be done in patients with sepsis.

General considerations

  • Patients should be urged to seek prompt care.
  • In the United States, physicians are required by law to report animal bites. 
  • Prophylaxis:
    • Tetanus immunization (if not up to date or unknown)
    • Rabies immunization (if animal status is unknown)

Wound management

  • Direct pressure to control bleeding 
  • Thorough wound irrigation
  • Explore deep tissues for tendon and bone damage.
  • Search for and remove foreign bodies.
  • Debride devitalized tissue.
  • Wound closure: 
    • Primary intention is indicated for:
      • Minimal damage
      • Easily cleaned
      • Low risk of infection
    • Secondary intention is suitable for:
      • Delayed presentation
      • Wounds on hands and feet
      • Contaminated wounds
      • Evidence of inflammation
      • Deep structure involvement

Management of infected wounds

  • Infections are usually polymicrobial.  
  • Antibiotic therapy:
    • Amoxicillin–clavulanate (first-line)
    • Doxycycline plus metronidazole
    • Trimethoprim–sulfamethoxazole plus metronidazole
    • Cephalosporins 
    • Broad-spectrum IV therapy for severe infections
  • Hospitalize patient for: 
    • Worsening cellulitis
    • Suspected sepsis
  • Consult specialist: 
    • Hand surgery
    • Infectious disease

Prophylaxis

Wounds at low risk for infection do not require antibiotic prophylaxis. Antibiotic prophylaxis is indicated for:

  • Deep puncture wounds
  • Crush injuries
  • Bites to the hand
  • Late presentation
  • Immunocompromised patients

Human Bites

Like dog and cat bites, human bites can carry a significant risk for infection.

Classification

  • Closed-fist injury (when the fist strikes the teeth on another individual)
  • Occlusive bite (when someone bites with sufficient force to break skin)

Microbiology

Infection after a human bite is often polymicrobial. Common organisms include:

  • Streptococcus
  • Staphylococcus
  • Eikenella corrodens
  • Corynebacterium
  • Bacteroides

Management

  • Extensive wound irrigation
  • Tetanus immunization
  • Amoxicillin–clavulanate prophylaxis should be given if the skin has been pierced.

Complications

  • Transmission of:
    • Hepatitis B
    • Hepatitis C
    • HIV
  • Tendon laceration
  • Infections (particularly closed-fist injury):
    • Tenosynovitis
    • Septic arthritis
    • Osteomyelitis
  • Cosmetic deformities

Differential Diagnosis

  • Snake bite: Envenomation at the bite site can cause edema, erythema, warmth, bullae, and necrosis. Systemic symptoms such as nausea, diaphoresis, paresthesias, and altered sensorium may be present, which are not common in dog or cat bites. The diagnosis is clinical. Management includes supportive care, pain control, hydration, and antivenom. Patients are monitored closely for shock, coagulopathy, respiratory failure, and renal failure.
  • Insect sting: Bee, wasp, and ant stings can cause envenomation with localized swelling. Some patients will develop a severe allergic reaction, including anaphylaxis. This does not occur with dog or cat bites. The diagnosis is clinical. Management includes removing the stinger (if present), antihistamines, pain control, and emergency care for anaphylaxis.
  • Scorpion sting: Most scorpion stings are harmless. However, the bark scorpion is venomous. Patients will have pain and swelling at the site of the sting. Systemic manifestations can include muscle spasms, diaphoresis, abnormal neck and head movements, tachycardia, hypertension, and respiratory distress. The diagnosis is clinical. Management includes supportive care, pain control, benzodiazepines for muscle spasms, and antivenom.
  • Spider bites: The brown recluse spider contains a necrotizing venom, which can lead to a painful, blistering, necrotic wound, fevers, myalgias, hemolysis, seizures, and renal failure. A black widow spider’s neurotoxic venom can cause muscle cramping and rigidity, unstable vital signs, lacrimation, salivation, ptosis, and respiratory distress. The diagnosis is clinical. Management includes wound care, pain management, antivenom for black widow bites, and delayed debridement of necrotic tissue for brown recluse bites.

References

  1. Holmquist L, Elixhauser A. (2010). Emergency department visits and inpatient stays involving dog bites. Healthcare Cost and Utilization Project Statistical Briefs. https://www.ncbi.nlm.nih.gov/books/NBK52650/
  2. Oehler RL, Velez AP, Mizrachi M, Lamarche J, Gompf S. (2009). Bite-related and septic syndromes caused by cats and dogs. Lancet Infect Dis. Medline. Retrieved March 25, 2021, from https://reference.medscape.com/medline/abstract/19555903
  3. Garth AP, Harris NS, Spanlerman CS, Salas RN. (2018). Animal bites in emergency medicine. In Alcock J. (Ed.). Medscape. Retrieved March 25, 2021, from https://emedicine.medscape.com/article/768875-overview
  4. Maniscalco K, Edens MA. (2020). Animal bites. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK430852/
  5. Barish RA, Arnold T. (2020). Human and mammal bites. MSD Manual Professional Version. Retrieved March 25, 2021, from https://www.msdmanuals.com/professional/injuries-poisoning/bites-and-stings/human-and-mammal-bites

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