ANIMAL BITE

Human and animal bites are the most common hand injuries, and most animal bites are from dogs or cats. A number of factors, including characteristics of the bite, age of the victim, bodily location of injury, time to presentation, severity of wound, and virulence of any inciting bacterium, must be considered when deciding on a treatment strategy. Bites to the hand are particularly deleterious owing to the close proximity of tendons, joints, cartilage and bone. Prompt treatment is always appropriate because, a delayed treatment may result in cellulitis, abscess, infectious tenosynovitis, septic arthritis and even sepsis. Primary concerns include the extent of injury and structures involved, animal type and vaccination status, and the patient’s overall health and tolerance to the injury.

Pathophysiology

• Pasturella multocida is the most prevalent bacterium in cat and dog bite wounds; however, other coexisting pathogens and/or patient comorbidities can increase the likelihood of complications, and in extreme cases, death.
• The bacteriology of dog and cat bite wounds is quite different, with that of dogs being more complex than that of cats.
  • In early studies, 32 aerobic and anaerobic organisms were isolated from dog bite wounds. By contrast, 11 were isolated from cat bite wounds.
• Other pathogenic organisms include Staphylococcus aureus, Streptococcal species, and Capnocytophaga canimorsus.

Wound Classification and Characteristics

• Wounds are graded I to III with Grade I wounds being more superficial and Grades II and III requiring hospitalization, surgery and follow-up: ^1,2
  • Grade I: Superficial lesion, torn or scratched skin, bite canal, crushing injury
  • Grade II: Wound extending from the skin to the tendon, muscle or cartilage and joint
  • Grade III: Wound with tissue necrosis or tissue loss
• Needle teeth of cats penetrate beneath skin into muscle and fascia; damage to the joint capsule, periosteum, and bone also have been reported.^1,2
• Dog bites will usually leave a more serrated wound.  Dogs have the ability to both tear and crush tissue and bone combined with a bite force greater than 300 pounds.²
• Pasturella species are the most common in dogs (50%) and cats.^1-4
• Differentiate high-risk wounds from low risk wounds:
  • High risk: cat bite wounds to the hand, particularly to the wrist; wounds involving joints, bone, and/ or neurovasculature of hand; patient having compromised health; displaying fever, lymphangnitis, erythema and swelling.⁵
  • Low-risk wounds: superficial wounds without signs of infection and/or involvement of the vital deeper hand anatomy in a patient with overall good health.¹
• If bacteria are present, infection will be apparent within 12-24 hours of the bite.  Infection will frequently be accompanied by rapid swelling, intense pain, and purulent discharge from the puncture site.
  • Cat bites may appear innocuous at first; however, a larger proportion of cat bite wounds become infected than do dog bite wounds.²
• Hospitalization is recommended in cases presenting with erythema, swelling and lymphangnitis.⁵

Related Anatomy

• Bodily structures involved will vary depending on the extent and location of the injury.
• Any bite involving the joints, tendons, ligaments, bones, nerves and/or vasculature of the hand becomes more problematic and consultation with hand surgeon is paramount.

Incidence and Related Conditions

• In the United States, the incidence of animal bites is 200 per 100,000 persons per year, corresponding to 1–2 million dog bites and 0.4 million cat bites.
  • More than 50% of the population will sustain an animal bite during their lifetime; of these bites, >90% are from domestic animals, including the family pet or a pet known to the patient.
  • Most animal bites occur during childhood (ages 6–17 y).
  • Most girls/women are bitten by cats; most boys/men are bitten by dogs.
• Bites from guinea pigs, rats, bats, monkeys and other non-domestic animals are less common.
• Rate of infection from cat bite wounds is double that observed from dog bites.
• 70–80% of animal bites are directed to the limbs.

Differential Diagnosis

• Spider bite (eg, brown recluse)
• Snake bite
• Rabies
• Tularemia (rat bite)
• Nail puncture or impaled on foreign body
• Mechanical injury involving machinery
• Previous injury resulting in infection

Patient Evaluation

• Assess tissue damage
  • Evaluate wound for involvement of bones, joints, tendons and/or neurovasculature.
  • Consider patient health, antibiotic history, and presence of any prosthetic joints or hardware where bacteria could seed.² (Kennedy et al, 2015)
  • Test hand mechanics²:
    • For bites to the dorsum of the proximal phalanx or PIP joint, perform the Elson test to ascertain potential disruption to extensor tendon mechanism
    • For bites to the dorsum of the hand or MP joint area, do an extensor lag test and general extensor examination to determine integrity of sagittal band
  • Imaging
    • Baseline radiographs and monitor for osteomyelitis^1,3  
    • High-resolution musculoskeletal sonography; ultrasound-guided aspiration^1-3
    • Doppler ultrasound to determine vascular damage³
  • Culture for aerobes and anaerobes using tissue specimens or aspirates in cases of infection²
  • Gram stain³
  • Blood work in conjunction with other exam findings: erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and white cell count (WBC)with differential
  • Photograph the wound
  • Obtain vaccination history of the animal^1,4,7,8
    • Rabies: dog bites are the most common source of rabies worldwide;^2,6  however, bats, raccoons, skunks and foxes are the most common carriers of rabies in the United States.^2,4  Stray cats are more likely to carry rabies in the United States than dogs.
    • Rabies immunoprophylaxis in cases of rabid animal bite^1,4
      • According to the CDC, no individual has been infected with rabies from a quarantined dog or cat which has been observed to stay healthy during the 10 day quarantine.  In this situation, the patient with the bite should not be vaccinated unless the animal develops signs of rabies.  If the dog or cat is rapid or suspected, then immediate vaccination is recommended.  If the bite source is unknown, the attending physician should consult with a public health officer.  For wild animal bites, i.e. bat or raccoon, consider vaccination.  Domestic animals like horses, rabbits or chipmunks do not usually carry rabies.
      • Immediately and thoroughly irrigate wound with 1% benzalkonium chloride or povidone iodine;² follow with copious saline irrigation⁴

• In severe cases, loss of tissue (fingertip), loss of joint mobility, and loss of motor and/sensory function have been reported.^1,2
• Chronic infection e.g. osteomyelitis,  septic joint 
• Capnocytophaga canimorsus can cause septic shock, organ failure and death.^1,2,3

• Favorable outcome can be anticipated with prompt treatment. In cases where presentation is either delayed, insufficient, or patient is noncompliant, persistent infection, joint destruction and osteomyelitis can be anticipated.²
• Once developed, rabies is almost always fatal.⁴
  • Physicians must report any rabid animal bites/attacks.¹
  • Consultation with the state veterinarian will instigate appropriate measures to contain the spread of the virus necessary to prevent an outbreak from occurring.^1,6

• Infection with Capnocytophaga canimorsus, although rare, can lead to sepsis, meningitis, endocarditis, disseminated intravascular coagulopathy, gangrene, acute respiratory distress syndrome, renal failure, organ damage, and death.^1,2,3
• The elderly and immunocompromised patients are most vulnerable to persistent and chronic infection leading to morbidity and potentially death.²
• Timing of wound closure is controversial,but delayed closure is the conservative option.³
• Risk factors: diabetes, chronic lung or liver disease, immunosuppression, delay in presentation and severity of wound.³
• Prophylactic antimicrobial therapy is warranted in high-risk cases such as puncture and hand wounds.⁴

Cited

1. Rothe K, Tsokos M, Handrick W. Animal and human bite wounds. Dtsch Arztebl Int 2015;112:433-43. PMID: 26179017
2. Kennedy SA, Stoll LE, Lauder AS. Human and other mammalian bite injuries of the hand: evaluation and management. J Am Acad Orthop Surg 2015;23(1):47-57. PMID: 25538130
3. Kwo S, Agarwal JP,  Meletious S. Current treatment of cat bites to hand and wrist. J Hand SurgAm 2011;36:152-53. PMID: 20006917
4. Dire DJ. Emergency management of dog and cat bite wounds. Emerg Med Clin North Am 1992;10(4):719-36. PMID: 1425400
5. Babovic N, Cayci C, Carlsen BT. Cat bite infections of the hand: assessment of morbidity and predictors of severe infection. J Hand Surg Am 2014;39(2):286-90. PMID: 24480688
6. Ellis R, Ellis C. Dog and cat bites. Am Fam Physician 2014;90(4):239-43. PMID: 25250997
7. https://www.cdc.gov/vaccines/hcp/vis/vis-statements/rabies.pdf
8. https://www.cdc.gov/rabies/exposure/animals/domestic.html

New Articles

1. Babovic N, Cayci C, Carlsen BT. Cat bite infections of the hand: assessment of morbidity and predictors of severe infection. J Hand Surg Am 2014;39(2):286-90.  PMID: 24480688
2. Kennedy SA, Stoll LE, Lauder AS. Human and other mammalian bite injuries of the hand: evaluation and management. J Am Acad Orthop Surg 2015;23(1):47-57. PMID: 25538130
3. Dedy NJ, Coghill S, Chandrashekar NKS, Bindra RR.  Capnocytophaga canimorsus sepsis following a minor dog bite to the finger; case report.  J Hand Surg Am 2016;41(1):81-84. PMID: 26710739

Reviews

1. Ellis R, Ellis C. Dog and cat bites. Am Fam Physician 2014;90(4):239-43. PMID: 25250997
2. Kwo S, Agarwal JP,  Meletious S. Current treatment of cat bites to hand and wrist. J Hand Surg Am 2011;36:152-53. PMID: 20006917

Classics

1. Dire DJ. Emergency management of dog and cat bite wounds. Emerg Med Clin North Am 1992;10(4):719-36. PMID: 1425400
2. Arons M, Fernando L, Polayes IM. Pasturella multocida – the major cause of hand infections following domestic animal bites. J Hand Surg 1982;7(1):47-52. PMID: 7061808