Bites - human and animal
Exam Tips
- Small dorsal MCP wounds after a fight are high risk: treat as joint/tendon-penetrating clenched-fist injuries until proven otherwise.
- Cat bites infect more often than dog bites because deep narrow punctures trap bacteria despite minor skin appearances.
- In OSCEs, score highly by documenting neurovascular status, tendon function through full range of motion, contamination, and exact mechanism/time of bite.
- Know first-line UK oral antibiotic: co-amoxiclav 500/125 mg TDS (3 days prophylaxis, 5 days treatment).
- Always address tetanus status and blood-borne virus/rabies risk where relevant.
- Image spotter: classic clenched-fist injury over the 3rd/4th MCP with minimal skin defect but deep structural risk (see standard hand trauma figure in surgical texts).
Definition
A human or animal bite is a traumatic wound caused by teeth, ranging from superficial abrasions to deep puncture, crush, avulsion, or degloving injury. In clinical practice, bite injuries are treated as both a trauma problem and a contamination problem because saliva inoculates polymicrobial flora into damaged tissue, creating a time-critical risk of local and systemic infection.
Pathophysiology
Bite injury combines mechanical tissue damage and microbial inoculation. Dog bites often produce crush/shear trauma with devitalized tissue and possible neurovascular, tendon, joint, or bone injury; cat bites create narrow deep punctures that seed bacteria into poorly draining spaces (higher infection risk); human bites (especially clenched-fist injuries over MCP joints) can penetrate extensor tendon/joint capsule despite a small skin wound. Infection is usually polymicrobial (aerobes + anaerobes): human bites commonly include Streptococcus spp, Staphylococcus aureus, Eikenella corrodens and anaerobes; animal bites often include Pasteurella species, with Pasteurella multocida particularly important in cat bites. Severe complications arise from progressive soft-tissue infection, contiguous spread to tendon sheath/joint/bone, or haematogenous/systemic spread (for example sepsis).
Risk Factors
- Delayed presentation or delayed wound toilet
- Deep puncture, crush, devitalized tissue, or significant tissue destruction
- Site: hand, foot, face, genitalia, or overlying a joint
- Clenched-fist ('fight bite') injury
- Cat bite (deep inoculation; higher infection rate than dog bites)
- Bone, tendon, joint, or vascular involvement
- Immunocompromise (including diabetes, asplenia, steroid/immunosuppressant use)
- Extremes of age, poor peripheral perfusion, chronic liver disease, alcohol excess
Clinical Features
Symptoms
- Pain at bite site, worsening tenderness, swelling
- Discharge, malodour, or reduced function of affected limb/digit
- Fever, rigors, malaise (suggesting systemic involvement)
- Reduced hand grip or painful finger movement after hand bites
- History of bite mechanism: occlusal vs clenched-fist injury, animal species, provoked/unprovoked event
Signs
- Visible puncture/laceration/avulsion/crush injury, sometimes deceptively small skin wound
- Erythema, warmth, induration, cellulitis, lymphangitis, regional lymphadenopathy
- Fluctuance or abscess, necrotic tissue, purulent exudate
- Reduced range of motion, tendon dysfunction, pain on passive movement (deep space/tendon sheath concern)
- Neurovascular deficit distal to wound
- Systemic toxicity or sepsis physiology in severe infection
Investigations
Management
Lifestyle Modifications
- Immediate first aid: irrigate thoroughly with running water or normal saline (high-volume lavage), remove visible debris, and avoid primary closure of high-risk wounds
- Elevation and immobilization of affected limb/hand to reduce swelling and pain
- Analgesia and clear safety-net advice (return urgently for spreading erythema, fever, increasing pain, reduced movement, or systemic symptoms)
- Document mechanism, timing, assailant animal/person details, and baseline photos/diagram for medico-legal accuracy
Pharmacological Treatment
Empirical antibiotic prophylaxis/treatment (adult oral first line)
- Co-amoxiclav 500/125 mg orally three times daily
Use 3 days for prophylaxis in high-risk but not yet infected wounds; 5 days for established infection (extend to 7 days if extensive tissue damage or slow response). Avoid in true penicillin allergy.
Penicillin-allergy oral alternative (adults)
- Doxycycline 200 mg on day 1, then 100 mg once daily (can increase to 200 mg daily) PLUS
- Metronidazole 400 mg orally three times daily
Covers mixed aerobic/anaerobic flora. Doxycycline is contraindicated in pregnancy and generally avoided in children under 12 years; counsel regarding photosensitivity and oesophagitis risk.
Severe infection / unable to take oral therapy
- Co-amoxiclav 1.2 g IV three times daily
Admit if systemic toxicity, deep hand-space involvement, suspected septic arthritis/osteomyelitis, rapidly progressive cellulitis, or immunocompromise. Step down to oral guided by clinical response/microbiology.
Tetanus prophylaxis
- Td/IPV vaccine 0.5 mL IM booster when indicated by immunization history and wound risk
- Human tetanus immunoglobulin 250 IU IM (500 IU IM if heavily contaminated or delayed presentation)
Assess every bite for tetanus risk, especially puncture/devitalized contaminated wounds.
Viral exposure prophylaxis (selected high-risk human bites or rabies risk exposure)
- HIV PEP: initiate urgently as per local specialist protocol when transmission risk is significant
- Rabies vaccine +/- rabies immunoglobulin for relevant bat/travel-related exposures
Human-bite HIV transmission risk is low but not zero; involve HIV/ID specialists early. UK terrestrial rabies risk is very low, but bat exposures and overseas bites require urgent UKHSA/public health advice.
Surgical / Interventional
- Urgent surgical/hand specialist referral for clenched-fist injuries, deep punctures to hand, tendon/joint/bone involvement, neurovascular compromise, abscess, necrotizing infection, or major tissue loss
- Formal exploration, washout, and debridement (often in theatre for hand/joint injuries)
- Drainage of abscess and management of septic arthritis/tenosynovitis as emergencies
- Delayed primary closure or healing by secondary intention for high-risk infected wounds; selected facial wounds may be closed early after meticulous irrigation and risk assessment
Complications
- Cellulitis and abscess formation
- Pyogenic flexor tenosynovitis
- Septic arthritis
- Osteomyelitis
- Necrotizing soft tissue infection
- Bacteraemia/sepsis, meningitis, endocarditis, organ abscess
- Tetanus (rare, but severe)
- Cat-scratch disease (Bartonella henselae)
- Rare viral transmission after human bite (hepatitis B/C, HIV, HSV)
- Functional impairment, scarring, and disfigurement
Prognosis
Most minor bites have good outcomes with prompt irrigation, risk stratification, and appropriate antibiotics when indicated. Prognosis worsens with delayed care, deep hand/joint involvement, immunocompromise, and missed clenched-fist injuries; severe systemic complications are uncommon but can be life-threatening. In the UK, death from dog bites is rare, but morbidity from infection and functional hand damage is clinically important.
Sources & References
💊BNF Drug References(4)
- Ceftriaxone[management.pharmacological]
- Co-amoxiclav[management.pharmacological]
- Doxycycline[management.pharmacological]
- Metronidazole[management.pharmacological]
✅NICE Guidelines(1)
- Bites - human and animal[overview]
📖Textbook References(20)
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1553)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 408)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1549, 1550)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1567)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1673)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1518)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1553)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1647)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1567)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1517)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1673)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1504)[context]
- Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 155)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 44)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 88)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 431, 432)[context]
- [Williams, Bailey and Love's Short Practice of Surgery] Norman Williams, Christopher Bulstrode, P Ronan O'Connell - Bailey & Love's Short Practice of Surgery 26E (2013, CRC Press) - libgen.li.pdf(pp. 56)[context]
- [Williams, Bailey and Love's Short Practice of Surgery] Norman Williams, Christopher Bulstrode, P Ronan O'Connell - Bailey & Love's Short Practice of Surgery 26E (2013, CRC Press) - libgen.li.pdf(pp. 141)[context]
- [Williams, Bailey and Love's Short Practice of Surgery] Norman Williams, Christopher Bulstrode, P Ronan O'Connell - Bailey & Love's Short Practice of Surgery 26E (2013, CRC Press) - libgen.li.pdf(pp. 44)[context]
- [Williams, Bailey and Love's Short Practice of Surgery] Norman Williams, Christopher Bulstrode, P Ronan O'Connell - Bailey & Love's Short Practice of Surgery 26E (2013, CRC Press) - libgen.li.pdf(pp. 91)[context]