Animal bites account for approximately 1% of all ED visits in the United States (~1.5 million annually), with dogs responsible for the majority, followed by cats and then humans. [1-2] The following is a comprehensive clinical summary for emergency medicine and primary care management.
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]
Immunizations
- Tetanus: Tdap/Td booster if >5 years since last dose for contaminated wounds; full primary series + TIG if never vaccinated [3]
- Rabies PEP: See Special Tests/Treatment sections below
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]
Severity stratification
- Low risk: Superficial abrasion/scratch, easily cleansed, non-hand/non-face location, immunocompetent patient
- Moderate risk: Laceration requiring closure, hand/face location, cat bite puncture
- High risk: Deep puncture, crush injury, joint/bone penetration, immunocompromised patient, signs of established infection
Complications: Wound infection (most common), abscess, septic arthritis, tenosynovitis, osteomyelitis, sepsis/DIC (especially Capnocytophaga in asplenic patients), meningitis, endocarditis, rabies [3][6][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
Discharge criteria
- Uncomplicated wound after irrigation and debridement
- Reliable patient with ability to follow up in 24–48 hours
- Appropriate antibiotics prescribed if indicated
- Tetanus and rabies prophylaxis addressed
Specialist consultation triggers
- Hand surgery/orthopedics: Hand bites, tendon injuries, joint penetration, fractures
- Plastic surgery: Complex facial lacerations, tissue loss requiring flap/graft
- Infectious disease: Refractory infection, Capnocytophaga sepsis, immunocompromised host
- Neurosurgery: Pediatric scalp bites with possible cranial penetration [3]
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]
References
1. Dog and Cat Bites: Rapid Evidence Review. — Ortiz DD, Lezcano FO. American Family Physician. 2023.
2. Dog and Cat Bites. — Ellis R, Ellis C. American Family Physician. 2014.
3. Bite-Related and Septic Syndromes Caused by Cats and Dogs. — Oehler RL, Velez AP, Mizrachi M, Lamarche J, Gompf S. The Lancet. Infectious Diseases. 2009.
4. FDA Drug Label. — Food and Drug Administration (DailyMed)..
5. Current Management of Acute Cutaneous Wounds. — Singer AJ, Dagum AB. The New England Journal of Medicine. 2008.
6. Capnocytophaga Zoonotic Infections: A 10-Year Retrospective Study (The French CANCAN Study). — Beauruelle C, Plouzeau C, Grillon A, et al. European Journal of Clinical Microbiology & Infectious Diseases : Official Publication of the European Society of Clinical Microbiology. 2022.
7. Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections: 2014 Update by the Infectious Diseases Society of America. — Stevens DL, Bisno AL, Chambers HF, et al. Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of America. 2014.
8. Infectious Complications of Bite Injuries. — Greene SE, Fritz SA. Infectious Disease Clinics of North America. 2021.
9. Antibiotic Prophylaxis in Trauma: Global Alliance for Infection in Surgery, Surgical Infection Society Europe, World Surgical Infection Society, American Association for the Surgery of Trauma, and World Society of Emergency Surgery Guidelines. — Coccolini F, Sartelli M, Sawyer R, et al. The Journal of Trauma and Acute Care Surgery. 2024.
10. Guide to Utilization of the Microbiology Laboratory for Diagnosis of Infectious Diseases: 2024 Update by the Infectious Diseases Society of America (IDSA) and the American Society for Microbiology (ASM). — Miller JM, Binnicker MJ, Campbell S, et al. Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of America. 2024.
11. Capnocytophaga Spp. Involvement in Bone Infections: A Review. — Piau C, Arvieux C, Bonnaure-Mallet M, Jolivet-Gougeon A. International Journal of Antimicrobial Agents. 2013.
12. Antibiotic Prophylaxis in Injury: An American Association for the Surgery of Trauma Critical Care Committee Clinical Consensus Document. — Appelbaum RD, Farrell MS, Gelbard RB, et al. Trauma Surgery & Acute Care Open. 2023.
13. Use of a Reduced (4-Dose) Vaccine Schedule for Postexposure Prophylaxis to Prevent Human Rabies: Recommendations of the Advisory Committee on Immunization Practices. — Rupprecht CE, Briggs D, Brown CM, et al. MMWR. Recommendations and Reports : Morbidity and Mortality Weekly Report. Recommendations and Reports. 2010.
14. FDA Drug Label. — Food and Drug Administration (DailyMed)..