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Emergency and Acute Medicine – Animal Bite
Overview
Most animal bites are provoked. Dogs cause the majority of bites, with large dogs responsible for the most severe injuries; pit bulls account for the highest number of fatalities. Children represent about 70% of fatalities, most often from bites to the face or neck. The majority of dog bites involve animals owned by family or friends. Cat bites usually involve household pets and have a high infection rate, approximately 50% among those seeking care, because of deep puncture wounds. Rat bites occur mainly in laboratory workers or children of low socioeconomic status. Rabies transmission from rats is rare, and prophylaxis is not routinely indicated.
Special Syndromes
Catscratch disease (CSD) is diagnosed when three of four criteria are present: contact with a cat and a scratch or inoculation lesion, positive catscratch skin test, characteristic lymph node histopathology, and exclusion of other causes of lymphadenopathy. Rat-bite fever (RBF) is uncommon in the United States but carries a high mortality rate and does not require an actual bite, as transmission may occur through handling rats.
Microbiology and Etiology
Dog and cat bites commonly involve Pasteurella multocida, found twice as often in cat bites as dog bites and present in up to 80% of cat bite infections, typically within 24 hours. Staphylococcus and Streptococcus infections usually appear after 24 hours. Other pathogens include anaerobes and Capnocytophaga canimorsus (dog bites). Catscratch disease is caused by Bartonella henselae. Rat-bite fever is caused by Spirillum minus and Streptobacillus moniliformis.
Epidemiology of Bites
Dog bites account for 80–90% of all mammalian bites, cat bites 5–15%, human bites 2–5%, and rat bites 2–3%.
Clinical Presentation
Dog bites most commonly cause crush injuries but may also produce tears, avulsions, punctures, and scratches. Infection rates are lower than with cat or human bites and typically present with cellulitis, malodorous gray discharge, fever, and lymphadenopathy. Cat bites usually cause puncture wounds and have infection rates of 30–50%. Catscratch disease begins with a small macule or vesicle that becomes a papule within 3–10 days, followed weeks later by tender, nonsuppurative regional lymphadenopathy that resolves over 2–4 months, often with low-grade fever and malaise. Rat-bite fever due to S. moniliformis presents 2–10 days after exposure with fever, rigors, migratory polyarthralgias, headache, nausea, and vomiting; S. minus has a 1–3 week incubation and is more common in Asia.
History and Examination
History should include animal behavior, provocation, ownership, location, time since injury, tetanus status, allergies, and immunocompromising conditions. Examination must document wound location and extent, swelling, crush injury, devitalized tissue, range of motion, tendon and nerve function, joint or bone involvement, and signs of infection including regional adenopathy.
Diagnostic Evaluation
Aerobic and anaerobic cultures are indicated for infected wounds but not for clinically uninfected bites. Catscratch disease may be confirmed by elevated Bartonella henselae titers or a positive catscratch antigen skin test, defined as induration ≥5 mm at 48–72 hours. Plain radiographs are indicated for suspected fractures, foreign bodies such as teeth, baseline evaluation of bone or joint space violation, and infection near bone or joints to assess for osteomyelitis.
Differential Diagnosis
Consider human bites, other animal bites, reactive lymphadenopathy, chronic lymphadenitis, infection, drug reactions, malignancy, and congenital causes of lymphadenopathy.
Prehospital and Initial Care
Apply direct pressure to control bleeding. In the emergency department, prioritize hemostasis and airway stabilization for bites to the face or neck.
Emergency Department Management
Irrigate wounds copiously with normal saline using an 18-gauge plastic catheter directed along the wound tract; avoid forceful injection into tissue planes. Débride foreign material, necrotic tissue, and eschar, but do not débride puncture wounds. Wound closure increases infection risk and must be individualized. Do not close infected wounds or wounds older than 24 hours. Facial wounds may be closed with patient counseling regarding infection risk. Infected wounds, delayed presentations, and deep hand wounds should be left open, with delayed primary closure if appropriate.
Antibiotic Therapy
Antibiotics are indicated for infected wounds, cat bites, hand injuries, crush injuries, puncture wounds, full-thickness wounds of hand, face, or lower extremity, wounds involving joints, tendons, ligaments, or fractures, immunocompromised patients, wounds requiring surgical débridement, and presentations more than 8 hours after injury. Elevate the affected extremity.
Tetanus and Rabies Prophylaxis
Update tetanus prophylaxis as indicated. Rabies prophylaxis is unnecessary unless rabies is suspected. Rodents and rabbits rarely transmit rabies; skunks, raccoons, bats, and foxes are major reservoirs.
Condition-Specific Treatment
Catscratch disease is usually self-limited; provide analgesia, local heat, and avoid lymph node trauma. Antibiotics are controversial but may be considered in severe disease or immunocompromised patients. Rat-bite fever requires IV penicillin or doxycycline due to significant mortality risk.
Medications
First-line options include amoxicillin–clavulanate orally, ampicillin–sulbactam IV, penicillin IV, piperacillin–tazobactam IV, ticarcillin–clavulanate IV, or ceftriaxone plus metronidazole. Second-line regimens involve combination therapy with trimethoprim–sulfamethoxazole, penicillin VK, ciprofloxacin, or doxycycline plus anaerobic coverage with clindamycin or metronidazole.
Disposition
Admit patients with infected wounds at presentation, severe or progressive cellulitis or lymphangitis, systemic infection, failure of outpatient therapy, or severe catscratch disease with prolonged fever or marked lymphadenopathy. Healthy patients with localized infection may be discharged on antibiotics with 24-hour follow-up. Noninfected wounds require follow-up within 48 hours.
Follow-Up and Referral
Refer infected hand wounds to a hand specialist. Ensure close follow-up as outlined above.
Key Clinical Cautions
Animal bites are reportable to authorities in many jurisdictions.
Overview
Most animal bites are provoked. Dogs cause the majority of bites, with large dogs responsible for the most severe injuries; pit bulls account for the highest number of fatalities. Children represent about 70% of fatalities, most often from bites to the face or neck. The majority of dog bites involve animals owned by family or friends. Cat bites usually involve household pets and have a high infection rate, approximately 50% among those seeking care, because of deep puncture wounds. Rat bites occur mainly in laboratory workers or children of low socioeconomic status. Rabies transmission from rats is rare, and prophylaxis is not routinely indicated.
Special Syndromes
Catscratch disease (CSD) is diagnosed when three of four criteria are present: contact with a cat and a scratch or inoculation lesion, positive catscratch skin test, characteristic lymph node histopathology, and exclusion of other causes of lymphadenopathy. Rat-bite fever (RBF) is uncommon in the United States but carries a high mortality rate and does not require an actual bite, as transmission may occur through handling rats.
Microbiology and Etiology
Dog and cat bites commonly involve Pasteurella multocida, found twice as often in cat bites as dog bites and present in up to 80% of cat bite infections, typically within 24 hours. Staphylococcus and Streptococcus infections usually appear after 24 hours. Other pathogens include anaerobes and Capnocytophaga canimorsus (dog bites). Catscratch disease is caused by Bartonella henselae. Rat-bite fever is caused by Spirillum minus and Streptobacillus moniliformis.
Epidemiology of Bites
Dog bites account for 80–90% of all mammalian bites, cat bites 5–15%, human bites 2–5%, and rat bites 2–3%.
Clinical Presentation
Dog bites most commonly cause crush injuries but may also produce tears, avulsions, punctures, and scratches. Infection rates are lower than with cat or human bites and typically present with cellulitis, malodorous gray discharge, fever, and lymphadenopathy. Cat bites usually cause puncture wounds and have infection rates of 30–50%. Catscratch disease begins with a small macule or vesicle that becomes a papule within 3–10 days, followed weeks later by tender, nonsuppurative regional lymphadenopathy that resolves over 2–4 months, often with low-grade fever and malaise. Rat-bite fever due to S. moniliformis presents 2–10 days after exposure with fever, rigors, migratory polyarthralgias, headache, nausea, and vomiting; S. minus has a 1–3 week incubation and is more common in Asia.
History and Examination
History should include animal behavior, provocation, ownership, location, time since injury, tetanus status, allergies, and immunocompromising conditions. Examination must document wound location and extent, swelling, crush injury, devitalized tissue, range of motion, tendon and nerve function, joint or bone involvement, and signs of infection including regional adenopathy.
Diagnostic Evaluation
Aerobic and anaerobic cultures are indicated for infected wounds but not for clinically uninfected bites. Catscratch disease may be confirmed by elevated Bartonella henselae titers or a positive catscratch antigen skin test, defined as induration ≥5 mm at 48–72 hours. Plain radiographs are indicated for suspected fractures, foreign bodies such as teeth, baseline evaluation of bone or joint space violation, and infection near bone or joints to assess for osteomyelitis.
Differential Diagnosis
Consider human bites, other animal bites, reactive lymphadenopathy, chronic lymphadenitis, infection, drug reactions, malignancy, and congenital causes of lymphadenopathy.
Prehospital and Initial Care
Apply direct pressure to control bleeding. In the emergency department, prioritize hemostasis and airway stabilization for bites to the face or neck.
Emergency Department Management
Irrigate wounds copiously with normal saline using an 18-gauge plastic catheter directed along the wound tract; avoid forceful injection into tissue planes. Débride foreign material, necrotic tissue, and eschar, but do not débride puncture wounds. Wound closure increases infection risk and must be individualized. Do not close infected wounds or wounds older than 24 hours. Facial wounds may be closed with patient counseling regarding infection risk. Infected wounds, delayed presentations, and deep hand wounds should be left open, with delayed primary closure if appropriate.
Antibiotic Therapy
Antibiotics are indicated for infected wounds, cat bites, hand injuries, crush injuries, puncture wounds, full-thickness wounds of hand, face, or lower extremity, wounds involving joints, tendons, ligaments, or fractures, immunocompromised patients, wounds requiring surgical débridement, and presentations more than 8 hours after injury. Elevate the affected extremity.
Tetanus and Rabies Prophylaxis
Update tetanus prophylaxis as indicated. Rabies prophylaxis is unnecessary unless rabies is suspected. Rodents and rabbits rarely transmit rabies; skunks, raccoons, bats, and foxes are major reservoirs.
Condition-Specific Treatment
Catscratch disease is usually self-limited; provide analgesia, local heat, and avoid lymph node trauma. Antibiotics are controversial but may be considered in severe disease or immunocompromised patients. Rat-bite fever requires IV penicillin or doxycycline due to significant mortality risk.
Medications
First-line options include amoxicillin–clavulanate orally, ampicillin–sulbactam IV, penicillin IV, piperacillin–tazobactam IV, ticarcillin–clavulanate IV, or ceftriaxone plus metronidazole. Second-line regimens involve combination therapy with trimethoprim–sulfamethoxazole, penicillin VK, ciprofloxacin, or doxycycline plus anaerobic coverage with clindamycin or metronidazole.
Disposition
Admit patients with infected wounds at presentation, severe or progressive cellulitis or lymphangitis, systemic infection, failure of outpatient therapy, or severe catscratch disease with prolonged fever or marked lymphadenopathy. Healthy patients with localized infection may be discharged on antibiotics with 24-hour follow-up. Noninfected wounds require follow-up within 48 hours.
Follow-Up and Referral
Refer infected hand wounds to a hand specialist. Ensure close follow-up as outlined above.
Key Clinical Cautions
Animal bites are reportable to authorities in many jurisdictions.
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