Infected Animal Bite

Infected animal bite is a bite or scratch wound by a mammal that becomes infected by oral flora or skin organisms. Dogs and cats account for most, but monkeys and baboons, rats, livestock (horses, camels, pigs), hyenas and wild carnivores cause notable injuries in Kenya.

• Pathogens differ by animal: Pasteurella (cats, dogs), Staphylococcus, Streptococcus, anaerobes, Capnocytophaga, Streptobacillus moniliformis and Spirillum minus (rat bite fever), Cercopithecine herpesvirus 1 or B virus (macaques).
• Rabies and tetanus must always be considered, and other zoonoses for exotic animals.

Pain, erythema, swelling and purulence at the bite, lymphangitis and fever; the time course varies from hours (Pasteurella) to days.

• Rat bite fever: fever, rash, migratory polyarthritis 3 to 10 days after the bite.
• Monkey bite: vesicles at the wound, neurological features if B virus encephalitis (1 to 3 weeks).
• Large animal bites cause crush injury, fractures, vascular injury and contamination.
• Differential diagnosis: non infected laceration, bacterial cellulitis, necrotising soft tissue infection, snake bite, insect envenomation, cat scratch disease, tularaemia, sporotrichosis, anthrax.
• Complications: abscess, tenosynovitis, septic arthritis, osteomyelitis, sepsis, necrotising fasciitis, endocarditis, tetanus, rabies, B virus encephalitis, scarring.

Clinical assessment of wound, animal and exposure.

• Wound swab (aerobic and anaerobic), blood cultures if febrile, full blood count, CRP.
• Radiograph or CT for bone injury, teeth fragments, gas; ultrasound for collections.
• Record species, provoked or unprovoked, vaccination status of the animal, and whether it can be observed for 10 days.

Wound care, selective antibiotics, tetanus and rabies prophylaxis, and pathogen specific therapy.

• Supportive: irrigation with at least 500 mL of sterile saline or clean water, debridement of devitalised tissue, leave wounds open (primary closure only for facial wounds after irrigation), elevate, analgesia, tetanus toxoid 0.5 mL IM if immunisation is out of date and tetanus immunoglobulin 250 units IM for dirty wounds.
• Pharmacological: amoxicillin clavulanate 625 mg three times daily for 3 to 5 days as prophylaxis, 7 to 14 days for established infection; severe infection: ampicillin sulbactam 3 g IV every 6 hours, or ceftriaxone 2 g IV daily plus metronidazole 500 mg IV every 8 hours. Penicillin allergy: doxycycline 100 mg twice daily with metronidazole 400 mg three times daily. Rat bite fever: benzylpenicillin 600,000 to 1.2 million units IV daily, or procaine penicillin 1.2 million units IM daily, for 7 to 14 days (doxycycline 100 mg twice daily if allergic). Monkey bite: valaciclovir 1 g three times daily for 14 days as post exposure prophylaxis against B virus, with wound cleaning for 15 minutes. Rabies post exposure prophylaxis for any bite from a mammal of unknown or unobservable status (dog, cat, monkey, hyena, bat, mongoose): wash with soap and water for 15 minutes; human rabies immunoglobulin 20 IU/kg infiltrated around the wound; vaccine intradermal 0.1 mL at two sites on days 0, 3 and 7, or intramuscular 1 mL on days 0, 3, 7 and 14.
• Procedures: surgical exploration, debridement and repair; drainage of abscess; vascular repair; fracture fixation.
• Special groups: pregnancy, amoxicillin clavulanate and rabies vaccine are safe; children, weight based doses and early admission for head, neck or hand bites; asplenia, alcohol dependence and immunosuppression, parenteral antibiotics; HIV, complete the rabies schedule and check antibody response.
• Red flags: deep wound over a joint or tendon, extensive crush injury, spreading redness, fever, bleeding from a large vessel, suspected rabid animal, neurological symptoms after monkey bite.
• Follow-up: review at 24 to 48 hours; complete vaccination schedules; observe the animal for 10 days where possible; surgical review for functional loss.