dog bite injury

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# 🐶 **DOG BITE – COMPLETE DETAILED MEDICAL NOTE**

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# **1. Definition**

A **dog bite injury** is trauma caused by teeth of a dog that may lead to:

* **Soft-tissue injury** (abrasions → deep lacerations)
* **Infection** with mixed aerobic/anaerobic flora
* **Rabies exposure** (most important fatal risk)
* **Tetanus contamination**
* **Crush injury + devitalization + risk of compartment syndrome**

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# **2. Pathophysiology**

### **A. Mechanical injury**

* Penetrating bite → skin & subcutaneous tissue tears.
* Strong jaw force → **crush injury**, avulsion, devascularization.
* Hand bites → high risk due to closed fascial spaces.

### **B. Microbial contamination**

Dog oral cavity flora includes:

* **Pasteurella multocida**
* **Capnocytophaga canimorsus**
* Staphylococcus, Streptococcus
* Anaerobes: Bacteroides, Fusobacterium
* Rare: MRSA

**Capnocytophaga** = severe sepsis risk in **asplenia, alcoholics, immunocompromised**.

### **C. Rabies**

Rabies virus inoculated through saliva → binds nicotinic receptors → retrograde axonal transport → CNS infection → encephalitis → death.

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# **3. Classification of Dog Bite (WHO Categories)**

### **Category I**

* Touching/feeding animal
* Licks on intact skin
➡ **No PEP required**

### **Category II**

* Nibbling of uncovered skin
* Minor scratches **without bleeding**
➡ **Rabies vaccine needed**
➡ No RIG

### **Category III**

* Single/multiple transdermal bites
* Deep wounds, lacerations
* Scratches with **bleeding**
* Saliva contamination of mucosa
➡ **Rabies vaccine + RIG mandatory**

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# **4. Risk Factors for Infection**

* Deep puncture wounds
* Hand & face bites
* Crush injuries
* Immunocompromised host
* Delay >8 hrs before cleaning
* Cat bites higher risk; dog bites moderate

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# **5. Clinical Features**

### **Local**

* Pain, swelling, erythema
* Warmth, tenderness
* Pus, foul discharge
* Tissue loss, tendon injury
* Numbness (nerve injury)

### **Systemic**

* Fever
* Lymphangitis
* Cellulitis
* Sepsis (esp. in Capnocytophaga)

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# **6. Complications**

### **Early**

* Cellulitis
* Abscess
* Necrotizing fasciitis
* Osteomyelitis
* Septic arthritis
* Tendon rupture
* Neurovascular injury
* Sepsis (Capnocytophaga)

### **Late**

* Rabies
* Tetanus
* Scarring & contractures
* PTSD in children

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# **7. Investigations**

Most cases = **clinical**.

### **Indicated in complicated wounds**

* CBC, CRP (if infection suspected)
* X-ray:

* Foreign body (teeth fragments)
* Fracture
* Gas (necrotizing fasciitis)
* Ultrasound:

* Abscess
* Wound culture:

* Only if infected

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# **8. Management (COMPLETE STEPWISE PROTOCOL)**

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## 🌟 **A. First Aid & Emergency Care**

### **1. Immediate wound washing (critical)**

* Wash for **15 minutes** with:

* Soap and running water
* Povidone-iodine or chlorhexidine

**Best immediate protection against both infection + rabies.**

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## 🌟 **B. Wound Care**

### **Examination**

* Depth, bleeding
* Devitalized tissue
* Location (hand = high risk)
* Tendon/joint involvement
* Neurovascular status

### **Debridement**

* Remove devitalized tissue
* Irrigate with **normal saline** (at least 500–1000 ml)

### **Wound Closure Decision**

| Wound | Recommendation |
| --------------------- | -------------------------------------- |
| Face | Primary closure (good vascularity) |
| Hand, feet, punctures | **Do NOT close** (high infection risk) |
| Large lacerations | Delayed closure |

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## 🌟 **C. Tetanus Prophylaxis**

### **Clean wound**

* If vaccinated within 5 years → **no booster**
* If >5 years → **Td/Tdap booster**

### **Dirty wound**

* If >5 years OR unknown → **Td/Tdap**
* If incomplete vaccination → **TIG + Td**

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## 🌟 **D. Antibiotic Therapy (VERY IMPORTANT)**

### **When Antibiotics Are Required**

* Deep wounds
* Hand/face/genitals
* Crush injuries
* Immunocompromised
* Delayed presentation
* All Category III bites

### **First-line (Adults)**

**Amoxicillin–Clavulanate 625 mg TID for 5–7 days**

### **Penicillin allergy**

* **Doxycycline 100 mg BID** + **Metronidazole 400 mg TID**
* OR
* **Clindamycin 300 mg QID** + **Ciprofloxacin 500 mg BID**

### **Children**

* Amoxicillin–Clavulanate:

* **25–45 mg/kg/day** in 2–3 divided doses

### **Infected wounds requiring IV**

* IV **Ampicillin–Sulbactam**
* Alternative: **Piperacillin–Tazobactam**, **Ceftriaxone + Metronidazole**

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# **9. Capnocytophaga Canimorsus (Must Know)**

Severe sepsis in:

* Asplenia
* Chronic alcoholism
* Immunocompromised

Treatment:

* IV **Penicillin G**
* If allergic: **Carbapenem** or **Ceftriaxone**

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# **10. Rabies Management (PEP – MOST IMPORTANT)**

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# **A. Rabies Vaccination Protocol (WHO 2024)**

### 💉 **Day 0 – 3 – 7 – 14 (IM regimen)**

Injection: **1 ml IM** in deltoid (anterolateral thigh in children).

Alternate schedule: **0–7–21 days**.

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# **B. Rabies Immunoglobulin (RIG)** – for **Category III**

### **Dose**

* **ERIG:** 40 IU/kg
* **HRIG:** 20 IU/kg

### **Administration**

* Infiltrate **as much as possible INTO/AROUND the wound**.
* Remaining volume → IM at a distant site.

**Never mix RIG and vaccine at the same site.**

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# **11. Pre-Exposure Prophylaxis (PrEP)**

For:

* Veterinarians / dog handlers
* Travelers to endemic regions
* Children with high exposure risk

**Schedule:**
Day 0 – Day 7
Booster after 1 year, then every 3 years.

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# **12. Special Situations**

### **Facial bites**

* High risk → **Category III**
* Primary closure allowed
* RIG mandatory

### **Hand bites**

* Do NOT close
* Always give prophylactic antibiotics

### **Immunocompromised**

* Give full RIG + vaccine regardless of wound category

### **Pregnancy**

* Rabies vaccine + RIG **safe**
* Give full PEP

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# **13. Patient Counselling**

* Immediate washing is life-saving
* Complete full course of vaccine
* Avoid alcohol and steroids during PEP
* Watch dog for **10 days** (if domestic)

* If healthy = no need to stop PEP once started
* Return urgently if:

* Fever, spreading redness
* Numbness, pus, severe pain

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# **14. Differential Diagnosis**

* Cat bites (higher infection risk)
* Human bites
* Snake/scorpion envenomation
* Cellulitis of other cause

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