Human and animal bites

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Bites combine crush, laceration, puncture and inoculation injury. A small skin mark can overlie deep tendon, joint, nerve or bone damage, especially on the hand.

Microbiology reflects the mouth of the biter and the skin of the injured person. Polymicrobial infection is common; Pasteurella can cause rapid animal-bite inflammation, while Eikenella makes some routine skin-antibiotic choices unreliable for human bites.

Antibiotic prophylaxis is based on wound and host risk rather than being automatic for every uninfected bite. Once infection is present, treatment and source-control decisions follow depth and severity.

Post-exposure prevention runs in parallel with wound care. Tetanus vaccination or immunoglobulin, rabies vaccine and immunoglobulin, and blood-borne-virus assessment have time-dependent pathways that should be completed before discharge.

Key points

Document species, ownership and health, location and country, provocation, time, wound mechanism and the patient's immune and vaccination status.
Immediate high-volume irrigation, removal of foreign material and appropriate debridement reduces inoculum and allows true depth assessment.
Examine distal perfusion, sensation, tendon function and joint movement before local anaesthetic or repair whenever possible.
Human bites contain oral streptococci, staphylococci, anaerobes and Eikenella; cat punctures commonly inoculate Pasteurella deep into tissue.
NICE first-choice oral prophylaxis and treatment is co-amoxiclav 625 mg three times daily: three days for prophylaxis and five days for treatment.
In penicillin allergy when pregnancy is excluded, NICE uses doxycycline 200 mg on day one then 100 to 200 mg daily plus metronidazole 400 mg three times daily.
Do not close infected, heavily contaminated or high-risk puncture wounds routinely; facial wounds and selected clean wounds need specialist closure judgment.
Assess tetanus for every wound, rabies for relevant mammalian or bat exposure and hepatitis B, hepatitis C and HIV risk after human bites involving blood.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Human oral flora

Streptococci, Staphylococcus aureus, Eikenella corrodens and anaerobes enter damaged tissue through direct bites or clenched-fist contact with human teeth.

Cat and dog flora

Pasteurella species, streptococci, staphylococci and anaerobes are inoculated, with cat teeth creating particularly narrow deep punctures.

Host and wound risk

Hand anatomy, poor perfusion, lymphoedema, diabetes, asplenia, liver disease and immune suppression increase infection severity or unusual-organism risk.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
High-inoculum implantation
Teeth force saliva and bacteria beneath the skin while crush injury reduces local perfusion and impairs innate bacterial clearance.
2
Closed-space spread
Punctures seal over and permit bacterial multiplication within tendon sheath, joint, deep hand space or periosteum under rising pressure.
3
Polymicrobial synergy
Aerobes consume oxygen and damage tissue while anaerobes flourish in devitalised low-oxygen spaces, creating abscess and malodour.
4
Systemic invasion
Untreated local infection can spread through lymphatics and blood, with Capnocytophaga causing fulminant sepsis particularly after dog exposure in asplenia.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Clenched-fist injuryRed flag

A small dorsal wound over a metacarpophalangeal joint after punching teeth may track through extensor tendon into the joint.

Cat puncture patternRed flag

Narrow deep punctures, particularly to hand or near a joint, can seal over and develop rapid Pasteurella cellulitis, tenosynovitis or abscess.

Dog crush and tearRed flag

Dog bites may cause irregular laceration, tissue devitalisation, fracture and nerve or vascular injury in addition to bacterial inoculation.

Established wound infection

Increasing pain, erythema, warmth, swelling, purulence, lymphangitis, malodour, fever or reduced function indicates treatment rather than prophylaxis.

Flexor sheath involvementRed flag

Fusiform swelling, flexed posture, tenderness along the sheath and pain on passive extension requires emergency hand-surgical evaluation.

Exposure prevention riskRed flag

Bat exposure, overseas mammalian bite, uncertain tetanus vaccination or human blood contamination triggers separate urgent prevention assessment.

Red flags requiring action

A clenched-fist wound over a metacarpophalangeal joint can penetrate tendon and joint despite a tiny opening.
Reduced movement, severe pain on passive motion or tendon dysfunction suggests sheath, joint or structural injury.
Absent pulse, delayed capillary return, sensory loss or uncontrolled bleeding requires emergency surgical assessment.
Fever, lymphangitis, rapidly spreading erythema or hypotension indicates invasive infection and possible sepsis.
Deep puncture to hand, face, genitals, foot or near a prosthetic joint has high functional or infection consequence.
An overseas mammalian exposure or bat contact requires urgent rabies-risk assessment without waiting for symptoms.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Wound exploration and functional examinationFirst step
Why
Define depth, devitalised tissue, retained tooth, tendon, joint, nerve and vascular injury.
Interpretation and limitations
Document tendon movement, two-point or relevant sensation, capillary return and joint testing before repair; inadequate examination warrants specialist exploration.
02
Deep wound culture
Why
Identify organisms and susceptibility when discharge or clinical infection is present.
Interpretation and limitations
Collect from deep tissue or pus after cleaning where possible. Do not routinely culture a clean uninfected bite or rely on a superficial skin swab.
03
Plain radiography
Why
Detect fracture, joint injury, gas, foreign body or retained tooth in penetrating and crush wounds.
Interpretation and limitations
Image when bone or joint penetration, deep hand injury or foreign material is possible; a normal film does not exclude tendon or early infection.
04
Ultrasound, CT or MRI
Why
Define abscess, deep-space infection, tendon injury or bone and joint extension when examination is incomplete.
Interpretation and limitations
Choose imaging with the surgeon for the anatomical question and do not delay exploration for obvious neurovascular compromise or septic joint.
05
Blood cultures and organ-function tests
Why
Assess systemic infection and safe intravenous treatment in fever or sepsis.
Interpretation and limitations
Obtain blood cultures before antibiotics when this causes no delay; renal and liver function affect antimicrobial dosing and operative risk.
06
Post-exposure risk assessment
Why
Determine need for tetanus, rabies and blood-borne-virus prophylaxis and baseline testing.
Interpretation and limitations
Use current UKHSA pathways with exposure country, animal, wound, vaccination and source information; specialist advice is time critical and should be documented.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Non-infected traumatic inflammation

Early pain, bruising and swelling after crush injury may occur without bacterial invasion but still requires structural and prophylaxis assessment.

Septic joint or tenosynovitis

Joint-centred restriction or pain along a tendon sheath indicates deep infection needing aspiration, washout or operative exploration.

Retained foreign body

Tooth fragment, claw, gravel or other material causes persistent pain and inflammation until identified and removed.

Allergic or venom reaction

Rapid itch, urticaria, wheeze or diffuse swelling after an arthropod or animal exposure suggests hypersensitivity rather than bacterial infection.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01CLEANIrrigate and define anatomyFirst stepAny human or animal bite has broken the skin or caused crush injury.

1Control bleeding, remove jewellery, provide analgesia and irrigate copiously with potable water or saline while removing visible contamination and foreign material.
2Record species, location, timing, provocation, country, animal availability, host immune status, allergies and vaccination history.
3Assess depth, tissue viability, perfusion, sensation, tendon function and joint penetration and obtain radiography when tooth, fracture or joint injury is possible.
4Refer hand, face, genital, neurovascular, tendon, joint, fracture or extensive-crush injuries for specialist exploration and closure decisions.

02PROPHYLAXISPrevent infection selectivelyA currently uninfected bite meets organism, anatomy, tissue-damage or host-risk criteria.

1Offer antibiotic prophylaxis for human bites drawing blood and consider it for high-risk non-bleeding human wounds under NICE criteria.
2Offer or consider prophylaxis for cat and dog bites according to depth, contamination, high-risk site, poor perfusion and comorbidity.
3Use co-amoxiclav 625 mg orally three times daily for three days when suitable, or the guideline allergy combination with pregnancy review.
4Arrange early wound review and explain that increasing pain, swelling, discharge, fever or loss of function changes the pathway to treatment and possible surgery.

03TREATTreat infection and control sourceThe bite is infected or deep structural involvement is suspected.

1Clean, debride and obtain a deep culture before antibiotics when feasible, then start co-amoxiclav for five days or appropriate intravenous treatment according to severity.
2Extend treatment only after review for slow response, deep structure involvement, poor perfusion or incomplete debridement rather than automatically.
3Drain abscess, wash out septic joint or tendon sheath and remove devitalised tissue or foreign body with the relevant surgical service.
4Review culture within 48 to 72 hours and narrow or change therapy while monitoring function, perfusion and systemic physiology.

04PREVENTComplete exposure prophylaxisThe wound is tetanus prone, involves human blood or follows a relevant mammalian or bat exposure.

1Check the complete tetanus vaccine record and wound category and give vaccine and tetanus immunoglobulin according to the current Green Book pathway.
2Contact the UKHSA rabies service urgently for risk assessment and, when advised, give vaccine with wound-infiltrated human rabies immunoglobulin according to exposure and prior vaccination.
3For human bites involving blood, assess source and recipient hepatitis B, hepatitis C and HIV risk and involve sexual-health or infection specialists for time-dependent prophylaxis.
4Document every product, batch, site and follow-up dose and provide written appointments because starting a course without completing it is inadequate prevention.

Key medicines and prescribing safety4 treatments · regimens, roles and cautions

NICE first-choice oral therapy covering common aerobic and anaerobic human, dog and cat oral flora.

Co-amoxiclav

Give 625 mg orally three times daily for three days as prophylaxis or five days as treatment for an adult bite wound.

Check immediate penicillin allergy, renal function and previous co-amoxiclav liver injury; review at 24 to 48 hours and extend only for a supported deep or slow response.

NICE alternative combination for penicillin allergy when pregnancy and individual contraindications have been addressed.

Doxycycline plus metronidazole

Give doxycycline 200 mg orally on day one then 100 to 200 mg daily, plus metronidazole 400 mg orally three times daily, for three prophylaxis days or five treatment days.

Avoid doxycycline in pregnancy, separate it from iron and antacids, counsel about photosensitivity and oesophagitis, and review metronidazole alcohol and warfarin interactions.

Provides broad initial bite-flora coverage while surgical assessment, deep culture and source control are arranged.

Intravenous co-amoxiclav

Give 1.2 g intravenously three times daily when severe infection, inability to take oral therapy or deep tissue involvement makes parenteral treatment necessary.

Check penicillin allergy, renal and hepatic function and local policy; review intravenous therapy within 48 hours and use wider cover only for supported resistant or healthcare-associated risk.

Prevents fatal rabies after a qualifying mammalian or bat exposure when started promptly and completed correctly.

Rabies vaccine and immunoglobulin

Use the exact current UKHSA post-exposure schedule; infiltrate the calculated human rabies immunoglobulin dose into and around wounds when indicated and give remaining vaccine doses on specified dates.

Contact the UKHSA rabies service for product, schedule and immunoglobulin decisions; previous vaccination, immune suppression and exposure category change management, and wound washing remains essential.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Deep hand infection

Tendon-sheath, web-space or joint infection causes adhesions, cartilage destruction, stiffness and permanent loss of hand function.

Osteomyelitis

Penetration to periosteum or delayed infection can seed bone and require debridement and prolonged organism-directed treatment.

Sepsis

Rapid local extension or bloodstream invasion can produce shock, particularly in asplenia, liver disease or immune compromise.

Tetanus or rabies

Inadequate post-exposure prevention permits toxin-mediated tetanus or fatal neuroinvasive rabies despite otherwise successful local wound bacterial treatment.

Blood-borne-virus transmission

Human bites involving blood can transmit hepatitis B and rarely other viruses, requiring exposure-specific testing and prophylaxis.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Review high-risk hand, cat puncture, immunocompromised and infected wounds within 24 to 48 hours even when initial treatment appears adequate.
At each review document erythema, swelling, discharge, pain, range of motion, tendon function, sensation and distal perfusion.
Check culture and susceptibility promptly and ensure oral therapy covers the relevant oral flora rather than defaulting to simple cellulitis treatment.
Escalate fever, lymphangitis, passive-movement pain, loss of function or progressive swelling for deep-space, tendon or joint assessment.
Verify tetanus, rabies and hepatitis B course completion and ensure HIV and hepatitis follow-up testing follows specialist advice.
After closure or repair monitor for infection, tissue necrosis, wound dehiscence and functional limitation and arrange hand therapy where needed.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

The tooth may enter the joint

During a punch, the metacarpophalangeal joint is flexed; the wound moves away from the injured tendon and capsule when the hand later extends.

Pasteurella can declare early

Rapid pain and inflammation within hours of a cat or dog bite should not be dismissed because the wound is small.

Eikenella changes drug choice

Human-bite flora are not reliably covered by flucloxacillin alone, making broad oral-flora coverage important when prophylaxis or treatment is indicated.

Closure is anatomical judgment

Cosmetic benefit may support carefully selected facial closure after irrigation, while puncture, infected and high-risk hand wounds are commonly left open.

Rabies prevention cannot wait

Once clinical rabies begins it is almost invariably fatal, so risk assessment and post-exposure prophylaxis must occur before symptoms.

Blood exposure is separate

A human bite can expose both people to blood; bacterial treatment does not replace hepatitis and HIV risk assessment.

11Common pitfallsFrequent interpretation and management errors.

01
Do not describe a clenched-fist wound as a superficial knuckle cut without examining tendon and joint through the range of motion.
02
Do not close an infected or heavily contaminated puncture wound routinely after a cursory wash.
03
Do not give flucloxacillin alone for a human bite when oral-flora coverage is required.
04
Do not take a superficial swab from an uninfected wound and prescribe against colonising growth.
05
Do not forget tetanus, rabies and blood-borne-virus assessment after finishing the bacterial prescription.
06
Do not reassure after a normal radiograph when tendon, sheath or joint penetration remains clinically possible.