Animal bite

1. History

• Type of animal: Dog, cat, wild animal, human; domestic vs. stray; vaccination status (especially rabies) [2-3]
• Circumstances: Provoked vs. unprovoked attack (unprovoked raises rabies concern); animal behavior (erratic, aggressive, nocturnal activity in diurnal species) [4]
• Timing: Time since bite — critical for wound closure decisions (<12 hours generally favorable for closure) and rabies PEP initiation [5]
• Location of bite: Hand, face, scalp, over joints, genitalia — each carries different infection and management implications [1]
• Wound type: Puncture (cat bites), crush/avulsion (dog bites), laceration, scratch [1]
• Symptom progression: Increasing pain, swelling, erythema, drainage, fever since injury
• Important negatives: Numbness, weakness, inability to move joints (tendon/nerve injury); no systemic symptoms (fever, rigors)

2. Alarm Features

• Rapidly spreading cellulitis, lymphangitis, or crepitus — concern for necrotizing infection
• Fever, rigors, sepsis — especially in asplenic, immunocompromised, or alcoholic patients → think Capnocytophaga canimorsus (31% case mortality in one series) [3][6]
• Loss of function in affected extremity (tendon laceration, septic arthritis, compartment syndrome)
• Bite over MCP joint ("fight bite"/clenched-fist injury) — high risk for joint space penetration [5]
• Unprovoked bite by wild animal or stray — high rabies risk [4]
• Bat exposure (even without visible bite) — rabies PEP indicated unless bat tests negative [4]
• Deep puncture wounds to the hand — infection rate up to 28–80% for cat bites [5]

3. Medications

Prophylactic antibiotics (3–5 days for high-risk bites): [1][7]

• First-line: Amoxicillin/clavulanate 875/125 mg PO q12h (adults); 45 mg/kg/day divided q12h (children) [1]
• Penicillin allergy: Clindamycin 300 mg TID + ciprofloxacin 500 mg BID (adults); clindamycin + TMP-SMX (children) [1]
• Pregnancy with penicillin allergy: Clindamycin + TMP-SMX (avoid TMP-SMX in 1st/3rd trimester); azithromycin as alternative but has variable Pasteurella activity [1]
• Inpatient IV options: Ampicillin-sulbactam, piperacillin-tazobactam, or a carbapenem [3]

Contraindicated as monotherapy for animal bites (poor Pasteurella coverage): dicloxacillin, cephalexin, clindamycin alone, erythromycin [3]

4. Diet

• No specific dietary triggers or restrictions
• Ensure adequate hydration and nutrition to support wound healing
• Patients on warfarin or anticoagulants should be counseled about potential drug interactions with prophylactic antibiotics (e.g., metronidazole, TMP-SMX, fluoroquinolones)

5. Review of Systems

• Constitutional: Fever, chills, malaise (infection/sepsis)
• Skin: Erythema, warmth, swelling, purulent drainage, lymphangitis
• MSK: Joint pain/swelling near bite (septic arthritis), decreased ROM, inability to flex/extend digits
• Neurologic: Numbness, tingling, weakness distal to wound (nerve injury); paresthesias at bite site progressing to hydrophobia/aerophobia (rabies — late)
• Vascular: Pulselessness, pallor distal to wound (vascular injury)

6. Collateral History and Family History

• Animal owner information: Vaccination status of animal, animal's current health, ability to quarantine/observe for 10 days [1]
• Contact local/state public health department for rabies risk assessment, especially for stray, wild, or escaped animals [3-4]
• Social context: Occupation (veterinarian, animal handler), living situation (homeless with stray animal exposure), immunocompromised household members
• Family history is generally not contributory, though inherited immunodeficiency or asplenia status is relevant

7. Risk Factors

High-risk wounds: [7-8]

• Cat bites (deep puncture mechanism; infection rate 28–80%) [5]
• Hand and foot wounds (28% infection rate without antibiotics vs. 2% with) [9]
• Puncture wounds (difficult to irrigate)
• Crush injuries with devitalized tissue
• Wounds involving tendons, joints, or bone
• Delayed presentation (>12 hours)

High-risk patients: [6-7]

• Immunocompromised (HIV, chemotherapy, transplant)
• Asplenic patients (high risk for fulminant Capnocytophaga sepsis)
• Advanced liver disease / chronic alcohol use
• Diabetes mellitus
• Preexisting edema of affected area
• Extremes of age

8. Differential Diagnosis

• Cellulitis/abscess from other causes (non-bite trauma, MRSA skin infection)
• Necrotizing fasciitis — rapidly progressive, crepitus, pain out of proportion
• Septic arthritis/osteomyelitis — if bite overlies a joint or bone [10-11]
• Tendon laceration — loss of function without infection
• Foreign body retention (embedded tooth fragment)
• Cat-scratch disease (Bartonella henselae) — subacute lymphadenopathy after cat scratch/bite
• Sporotrichosis — nodular lymphangitis after animal scratch
• Non-accidental trauma — especially in children; bite pattern inconsistent with stated mechanism

9. Past Medical History

• Splenectomy or functional asplenia — dramatically increases risk of overwhelming Capnocytophaga sepsis [3][6]
• Immunosuppressive therapy (steroids, biologics, chemotherapy)
• Diabetes mellitus, chronic liver disease, chronic kidney disease
• Prior bite history and any complications
• Tetanus and rabies vaccination history
• Prosthetic joints or hardware near bite site

10. Physical Exam

• Vital signs: Fever, tachycardia, hypotension (sepsis)
• Wound assessment: Type (puncture, laceration, avulsion, crush), depth, size, location; presence of devitalized tissue, foreign bodies, exposed bone/tendon [1][3]
• Neurovascular exam: Distal pulses, capillary refill, sensation (two-point discrimination), motor function of tendons crossing the wound [1]
• Joint assessment: ROM of adjacent joints; assess for joint capsule penetration (saline load test if concern for joint involvement)
• Lymph node exam: Regional lymphadenopathy
• Signs of infection: Erythema, warmth, induration, fluctuance, purulent drainage, lymphangitis, crepitus
• Mark wound borders with pen to monitor for spreading cellulitis

11. Lab Studies

• Routine labs generally not required for uncomplicated bites [1]
• If infection present or suspected:
  • CBC with differential, CRP, ESR
  • Blood cultures (if systemic signs/sepsis) — critical for identifying Capnocytophaga, Pasteurella bacteremia [3][10]
  • BMP (renal function for antibiotic dosing)
  • Wound culture: Gram stain + aerobic and anaerobic cultures from deep wound aspirate or tissue (not superficial swabs) — indicated only for clinically infected wounds, not prophylactically [10]
  • Lactate if sepsis concern
• Coagulation studies if significant hemorrhage or DIC suspected (Capnocytophaga sepsis)

12. Imaging

• Plain radiographs: First-line if suspicion for fracture, foreign body (retained tooth), bony penetration, or osteomyelitis [3]
• CT or MRI: If concern for deep space infection, abscess, osteomyelitis, or joint penetration [3]
• Imaging generally unnecessary for superficial, uncomplicated bite wounds [1]
• Ultrasound: Can be useful for identifying superficial abscess or foreign body at bedside

13. Special Tests

• Saline load test: Inject sterile saline into adjacent joint to assess for capsule penetration (if saline leaks from wound, joint is violated)
• Wound exploration: Assess tendon integrity through full ROM; explore through full range of motion the hand was in at time of injury (especially for fight bites over MCP joints)
• Rabies risk assessment algorithm: [1]
  • Animal available → 10-day quarantine/observation
  • Animal unavailable/escaped → consult public health for rabies risk assessment
  • Wild animal (bat, skunk, raccoon, fox) → presume rabid unless tested negative
  • Small rodents/lagomorphs → almost never rabid in the US [4]

14. ECG

• Not routinely indicated for animal bites
• Consider if sepsis develops (evaluate for tachyarrhythmia, signs of myocarditis)
• Obtain if planning procedural sedation for wound repair

15. Assessment

Animal bites are polymicrobial wounds containing a mix of aerobes and anaerobes from the animal's oral flora and the patient's skin flora. [3] Key pathogens include Pasteurella spp. (especially P. multocida in cat bites, P. canis in dog bites), Capnocytophaga canimorsus (dogs), streptococci, staphylococci (including MRSA), and various anaerobes. [3][10]

16. Treatment Plan

Initial wound management: [1-3]

• Copious irrigation: Normal saline or tap water using a 20-mL syringe with 18–20 gauge catheter for high-pressure irrigation
• Debridement: Remove devitalized tissue and foreign bodies
• Wound exploration: Assess depth, tendon/nerve/vessel/bone involvement

Wound closure: [5][7]

• Face wounds: Primary closure after copious irrigation + prophylactic antibiotics (low infection risk due to rich blood supply)
• Low-risk lacerations (<12 hours old, non-hand): May be closed primarily
• High-risk wounds (punctures, hand bites, cat bites, crush injuries, >12 hours old): Leave open for secondary intention or delayed primary closure at 3–5 days
• Clenched-fist injuries: Never close primarily [5]

Antibiotic prophylaxis (3–7 days) — indicated for: [7][12]

• All cat bites (deep puncture mechanism)
• Hand or foot wounds
• Immunocompromised, asplenic, advanced liver disease
• Moderate-to-severe injuries
• Wounds penetrating periosteum or joint capsule
• Wounds with significant crush component or edema

Established infection — requires: [3]

• IV antibiotics: Ampicillin-sulbactam, piperacillin-tazobactam, or carbapenem
• Surgical debridement and drainage if abscess present
• Deep wound cultures (aerobic + anaerobic) before starting antibiotics

Rabies PEP (for previously unvaccinated): [1][4][13]

• HRIG: 20 IU/kg — infiltrate as much as possible into and around the wound; remainder IM at distant site from vaccine
• Rabies vaccine: 1 mL IM on days 0, 3, 7, and 14 (4-dose ACIP schedule for immunocompetent); 5 doses (add day 28) for immunocompromised [13-14]
• Previously vaccinated: 2 doses on days 0 and 3; no HRIG [4]

Tetanus prophylaxis: Per standard guidelines based on wound type and vaccination history [3]

17. Disposition

Admission criteria: [3]

• Fever, sepsis, or septic shock
• Spreading cellulitis or lymphangitis not responding to oral antibiotics
• Significant crush injury or tissue loss requiring surgical management
• Loss of function (tendon/nerve injury requiring operative repair)
• Septic arthritis or osteomyelitis
• Immunocompromised patient with moderate-to-severe bite
• Noncompliance concerns or inability to follow up

18. Follow Up / Return Precautions

• Wound recheck at 24–48 hours — this is critical, as most bite wound infections manifest within 24–72 hours [3]
• Pasteurella infections typically present within 24 hours; other bacterial infections may take 2–3 days
• Return precautions: Increasing redness, swelling, warmth, drainage, red streaking, fever >100.4°F, worsening pain, decreased function of affected area
• Complete rabies vaccine series on schedule if initiated (days 0, 3, 7, 14) [13]
• Animal observation: Confirm 10-day quarantine outcome with animal control/public health [1]
• Counseling: Animal safety education (especially for children); consider PTSD screening after severe attacks [3]
• Expected recovery: Uncomplicated wounds typically heal within 1–2 weeks; hand wounds may require prolonged immobilization and physical therapy

Reporting: Most states require physicians to report animal bites to local animal control or public health authorities. [2]