Background Information
Aetiology
Organisms implicated in human bites: [Ref]
- Eikenella corrodens – most common
- Aerobes (e.g. Staphylococcus aureus, Streptococcus species)
- Anaerobes (e.g. Fusobacterium, Peptostreptococcus, Prevotella, and Porphyromonas species)
Organisms implicated in animal bites (mainly dogs and cats): [Ref]
- Pasteurella species (Pasteurella canis in dogs and Pasteurella multocida in cats) – most common
- Capnocytophaga canimorsus (dogs)
- Streptococci, staphylococci, Moraxella, and saprophytic Neisseria species
Animal bite wounds are also often polymicrobial, with a mix of aerobes and anaerobes
Management
There are 3 main domains to consider regarding the management of human and animal bites
1. Antibiotic Therapy
Decision Algorithm
If the wound is infected → offer antibiotics to all patients
If the wound is NOT infected → do not routinely give antibiotics, depending on the severity of the bite (3 severities) and the type of bite (3 types):
| The bite did not break the skin → | Human bite → | Do not offer antibiotics |
| Cat bite → | ||
| Dog or other traditional pet bite → | ||
| The bite broke the skin but did not draw blood → | Human bite → | Consider antibiotics if at a high-risk areaHigh-risk areas include hands, feet, face, genitals, skin overlying cartilaginous structures or an area of poor circulation / person is at high riskE.g. diabetes, immunosuppression, asplenia, decompensated liver disease |
| Cat bite → | Consider antibiotics if the wound is deep | |
| Dog or other traditional pet bite → | Do not offer antibiotics | |
| The bite broke the skin and drew blood → | Human bite → | Offer antibiotics |
| Cat bite → | ||
| Dog or other traditional pet bite → | Only offer antibiotics if:
Consider antibiotics if at a high-risk areaHigh-risk areas include hands, feet, face, genitals, skin overlying cartilaginous structures or an area of poor circulation / person is at high riskE.g. diabetes, immunosuppression, asplenia, decompensated liver disease |
Human and cat bites usually need antibiotics due to high infection risk.
Dog bites are less likely to require antibiotics, as they tend to cause more superficial crushing injuries rather than deep puncture wounds.
Choice of Antibiotics
In adults:
- 1st line: co-amoxiclav
- 2nd line: doxycycline + metronidazole
Children:
- 1st line: co-amoxiclav
- 2nd line: co-trimoxazole
2. Tetanus Post-Exposure Prophylaxis (PEP)
Decision-making for tetanus PEP is based on whether the patient has received an adequate priming course, which is defined as ≥3 doses of a tetanus vaccine.
This is not the same as the full UK tetanus immunisation schedule, which consists of 5 doses given at set intervals to provide long-term protection.
The decision regarding whether tetanus PEP is required depends on 2 factors:
- Immunisation status – did the patient receive an adequate priming course (≥3 doses of tetanus vaccine) and is the last dose <10 years ago?
- Wound type
| Clean wound | ALL the following:
|
| Tetanus-prone wound | Including any of the following:
|
| High-risk tetanus-prone wound | Any of the tetanus-prone wound features AND any of the following:
|
There are two ways to present this decision algorithm. The first table is designed for intuitive learning and may be helpful for some students, while the original guideline table is also included for reference. Both tables convey the same core information, so students can choose whichever format suits their learning style best.
Student-Friendly Version
One of the most important thing is to learn when PEP is NOT necessary:
- PEP is NOT necessary in only 2 situations: 1) patients received adequate priming <10 years ago, 2) patients received adequate priming >10 years ago, and have a clean wound
- All other patients would need some form of PEP – vaccine booster +/- tetanus immunoglobulin
| Immunisation status | Management |
|---|---|
| Patient received ≥3 doses of tetanus vaccine (adequate priming) | Management depends on when the last dose of vaccine was:
|
| Vaccination status unknown / inadequate priming |
|
Original Guideline Version
| Immunisation status | Clean Wound | Tetanus-prone wound | High-risk tetanus-prone wound |
|---|---|---|---|
| ≥3 doses (adequate priming) + last dose <10 years ago | No PEP required | ||
| ≥3 doses (adequate priming) + last dose >10 years ago | No PEP required | Give a vaccine booster | Give vaccine booster + tetanus immunoglobulin |
| Vaccination status unknown / inadequate priming | Give a vaccine booster | Give vaccine booster + tetanus immunoglobulin | |
3. Rabies Post-Exposure Prophylaxis
Note that rabies is almost always transmitted from infected animals (most commonly dogs, bats, raccoons, foxes), not from humans.
Key point: If a person is bitten by a common animal (e.g. dogs, cats) in the UK, and NOT by bats or primates or rodents → no rabies PEP is necessary (regardless of exposure and immunisation status)
Otherwise, the decision algorithm is rather complicated, depending on:
- Animal
- Type of exposure
- Composite rabies risk
- Person’s immunisation status
Students are not expected to memorise the full decision-making algorithm for rabies exposure. In clinical practice, a rabies post-exposure treatment request form is provided, and you simply complete it according to the exposure details.
As a key concept, if the patient is at high risk of contracting rabies (i.e. high-risk exposure Any bite that breaks the skin (terrestrial mammals) Severe or deep lacerations Licks to mucous membranes (eyes, mouth) Bats Scratches Saliva contacting mucous membranes Urine contacting mucous membranes Bats (worldwide; UK and Ireland bats relatively low risk) Dogs Foxes Skunks Raccoons Wolves Jackals Wild cats Any laboratory-confirmed rabid animal Most of Asia and Africa.
, high-risk animal
- If the patient is immunised → give further vaccine course
- If the patient is not fully immunised / immunocompromised → give full course of vaccine + human rabies immunoglobulin
References
NICE guideline Human and animal bites: antimicrobial prescribing
UK Health Security Agency Guidance on Rabies post-exposure treatment: management guidelines