Summary

Mammalian bites (Dog, Cat, Human) are common injuries with significant infection risk due to inoculation of oral flora deep into tissues. Dog bites are most common; Cat bites are small punctures but highly prone to infection; Human bites (especially the "Fight Bite" – Clenched fist injury over MCP joint) carry the worst prognosis due to joint penetration. Key organisms include Pasteurella multocida (Dogs/Cats), Capnocytophaga canimorsus (Dogs – Especially dangerous in Asplenic/Immunocompromised), and Eikenella corrodens (Human bites). Management includes thorough wound irrigation, appropriate antibiotic prophylaxis (Co-Amoxiclav is first-line), Tetanus prophylaxis, assessment for Rabies risk, and careful consideration of wound closure (Facial bites usually closed; Hand/puncture wounds often left open).

Key Facts

• Dog Bites: Most common. Crush injuries. Pasteurella. Capnocytophaga (Asplenic).
• Cat Bites: Deep punctures. High infection rate (30-50%). Pasteurella (Fast onset).
• Human Bites: "Fight Bite" = Clenched fist injury. Eikenella corrodens. High complication rate.
• Antibiotic: Co-Amoxiclav (Covers Pasteurella, Staph, Strep, Eikenella, Anaerobes).
• Closure: Facial bites – Close (Good blood supply). Hand/Puncture – Leave open or delayed closure.
• Tetanus: Booster if >10 years (or >5 years if dirty wound).
• Rabies: Assess risk (Animal source, Country, Vaccination status).

Clinical Pearls

"Fight Bite = Septic Arthritis Until Proven Otherwise": A wound over MCP in a clenched fist position likely penetrated the joint capsule. Treat aggressively.

"Cat Bites Infect Fast": Small punctures inoculate bacteria deep. Infection develops within 24 hours.

"Capnocytophaga in Asplenic Patients = Fulminant Sepsis": Dog bites in asplenic patients can cause rapid, fatal septicaemia.

"Co-Amoxiclav Covers Everything": First-line antibiotic for mammalian bites.

Why This Matters Clinically

Bites cause significant morbidity. Early recognition of high-risk wounds (Cat bites, Human fight bites, Immunocompromised host) and prompt antibiotic therapy prevent serious complications.

Organisms by Bite Type

Special Organisms

Asplenic / Hyposplenic Patients

Immunocompromised (Diabetes, Cirrhosis, Steroids, HIV)

• Higher infection risk.
• Lower threshold for antibiotics.

Key Guidelines

Scenario 1:

• Stem: A man punched another person in the mouth. He presents with a wound over his right 4th MCP joint. What is the diagnosis and management?
• Answer: Fight Bite (Clenched Fist Injury). High risk of septic arthritis. X-Ray (Tooth fragment). Admit. IV Co-Amoxiclav. Washout in theatre.

Scenario 2:

• Stem: A woman is bitten on the hand by a cat. 12 hours later, she has swelling, redness, and purulent discharge. What organism is most likely?
• Answer: Pasteurella multocida (Rapid onset cellulitis from cat bite).

Scenario 3:

• Stem: What antibiotic is first-line for mammalian bite wounds?
• Answer: Co-Amoxiclav (Covers Pasteurella, Eikenella, Staph, Strep, Anaerobes).

What should I do if I'm bitten?

1. Clean the wound: Wash thoroughly under running water for at least 5 minutes.
2. Seek medical attention: Especially for cat bites, hand bites, or large wounds.
3. Antibiotics: You may need a course to prevent infection.
4. Tetanus: Make sure your vaccinations are up to date.

When should I worry?

• Wound getting redder, more swollen, or more painful.
• Pus or discharge.
• Fever or feeling unwell. Go back to the doctor or A&E if this happens.

Key Counselling Points

1. Complete Antibiotic Course: "Finish all the antibiotics even if it looks better."
2. Watch for Worsening Signs: "Come back if it gets redder, more swollen, or you feel unwell."
3. Elevate Hand: "Keep your hand raised to reduce swelling."

• Pasteurella first described late 19th Century. Named for Louis Pasteur.
• Capnocytophaga Sepsis: Increasingly recognised from 1970s. High mortality in asplenic patients.