Animal bites

What is the most likely organism to infect animal bite wounds?

Pasteurella Multocida

Clinical

• rapid evolution of an intense inflammatory response
• with substantial pain and swelling
  • in 70% within 24 hours of the initial injury in 70% of cases
  • in 90% by 48 hours
• Infections usually exhibit localized cellulitis and purulent discharge.
• has resulted in abscess formation, septic arthritis, osteomyelitis, sepsis, meningitis, endocarditis, and pneumonia.
• Fever, regional adenopathy, and lymphangitis are seen in fewer than 20% of patients.
• Wounds in proximity to bones or joints may be associated with the complications of septic arthritis, osteomyelitis, and tenosynovitis.
• If there is edema of the extremity, the risks of sepsis and serious cellulitis are increased. 

Microbiology

• facultatively anaerobic, bipolar staining, gram-negative coccobacillus
• is a primary pathogen in animals.
• found in the oral flora of 70% to 90% of cats, 25% to 50% of dogs, and the mouths of many other animals.
• Transmission occurs from the bite or scratch of a cat, dog, or less commonly, other animal.
• Cats cause only 5% of bites presenting to emergency departments, but these bites are associated with a high risk of infection (80%)*
• Dogs cause the majority (90%) of bites presenting to emergency departments but are associated with a low risk of infection (5%)*
• vs Chief Pearl: The rate of infection after a dog bite is about 15-20% (just like human bites), and cat bites have an infective rate of >/= 50%
• Respiratory spread from animals to humans also occurs.
• Human-to-human spread has not been documented.
• the incubation period usually is less than 24 hours.
• can be isolated from skin lesion drainage or other sites of infection.
• laboratory differentiation is not difficult, although ~ resembles several other organisms morphologically (eg, Haemophilus influenzae, Neisseria sp, and fastidious gram-negative rods, particularly Actinobacillus) and grows on many culture media at 98°F (37°C).

When to suture? When to Xray? When to refer?

• In general, recent, apparently noninfected, low-risk lesions may be sutured after thorough wound cleansing, irrigation, and debridement (although some prefer to approximate the wound edges with adhesive strips or tissue adhesive).   
• Hand and foot bites
  • have a greater chance of becoming infected and should have surgical evaluation.  When to refer to a hand surgeon: if suspicion of underlying tendon or bony compromise.
  • Radiographs are indicated for a patients whose hands have been bitten by an animal.   X-rays may reveal occult fx or foreign bodies.
  • All hand wounds should be left open (increased risk of infection).
• Face bite wounds
  • rarely become infected
  • because of the cosmetic implications, should be closed whenever possible.
  •  Radiographs are indicated for children who have been bitten on the scalp or face. X-rays may reveal occult fx or foreign bodies
• Puncture wounds should be left open (increased risk of infection)
• Human bites: see below

Tetanus

• Everybody bitten by an animal are at risk for tetanus. If no boosters in last 5 years, give 0.5 mL Td. If doesn't have primary immunization complete, give tetanus Ig (250 U IM)
• see Tetanus and Wound Care

Antiobiotic prophylaxis

• The drug of choice: amoxicillin-clavulanate.  Give one dose of unasyn IV and 3-5 days of augmentin¹. Treat the following (Red Book)
  • Moderate or severe bite wounds, especially if edema or crush injury is present
  • Puncture wounds, especially if penetrating bones, tendon sheath, or joint has occurred
  • Facial bites
  • Hand and foot bites
  • Genital area bites
  • Wounds in immunocompromised and asplenic patients
• For penicillin-allergic adults: cefuroxime 500 bid or (clinda 300 q4h + cipro 500 bid)¹
• For penicillin-alergic children: cefurox 30/kg div bid or (clinda + bactrim)¹
• Other effective agents include penicillin, ampicillin, cefuroxime, cefpodoxime, trimethoprim-sulfamethoxazole, and tetracycline.
• The duration of therapy usually is 7 to 10 days for local infections and 10 to14 days for more severe infections.
• Wound drainage or debridement may be necessary.

Followup should be in 24-48h to eval for infxn

Antibiotic treatment in special cases

• Many human bites are clenched fist injuries, which are particularly high infection risks. Amoxicillin/clavulanate is recommended as above. Consider passive immunization for hepatitis B with immune globulin. In high-risk exposures (eg, known HIV-positive patient, hollow bloody needle from high-risk patient), the recommended 3-drug regimen (ie, zidovudine [ZDV] plus lamivudine [3TC] plus indinavir [IDV]) should begin within 60 minutes of exposure. Other retroviral agents can be substituted for these agents. However, nevirapine is not recommended because of several reported cases of life-threatening hepatotoxicity occurring during prophylaxis.
• Treat splenectomized patients who have been bitten by a dog with prophylactic penicillin due to increased risk of sepsis and death due to the rare bacterial species Capnocytophaga canimorsus*
• For patients allergic to beta-lactam agents, tetracycline is effective, but it should not be administered to children younger than 8 years of age.
• For polymicrobial infection, which frequently involves Staphylococcus aureus, oral amoxicillin-clavulanate or intravenous ampicillin-sulbactam or ticarcillin-clavulanate (for severe infection) can be given.
• Parenterally administered broad-spectrum cephalosporins, such as cefotaxime or cefoxitin, are active against P multocida in vitro, but the therapeutic experience with these drugs for these infections is limited.

Other organisms. The incubation period for infections caused by these pathogens is longer than P multocida; symptoms most likely would not be apparent within 24 hours of an animal bite.

• Anaerobes. Eikenella corrodens is an anaerobic organism found in the oral flora of humans. It frequently causes infections in human bite wounds, but it is not usually a pathogen in animal bites.
• Francisella tularensis most commonly is acquired from a tick bite or from contact with infected animal carcasses.
• Both S aureus and Streptococcus pyogenes are frequent causes of skin infection and may complicate animal bites.
• Capnocytophaga species
• Moraxella species
• Corynebacterium species
• Neisseria species

References:

American Academy of Pediatrics. Pasteurella multocida infections. In:
Pickering LK, ed. 2000 Red Book: Report of the Committee on Infectious
Diseases. 25th ed. Elk Grove Village, Ill American Academy of
Pediatrics; 2000:426-427
American Academy of Pediatrics. Bite wounds. In: Pickering LK, ed.
2000 Red Book: Report of the Committee on Infectious Diseases. 25th
ed. Elk Grove Village, Ill: American Academy of Pediatrics;
2000:155-158
Garcia VF. Animal bites and Pasteurella infections. Pediatr Rev.
1997;18:127-130
Ginsberg CM. Animal and human bites. In: Behrman RE, Kliegman RM,
Jenson HB, eds. Nelson Textbook of Pediatrics. 16th ed. Philadelphia,
Pa: WB Saunders Co; 2000:790-793
*http://www.emedicine.com/emerg/topic803.htm#target2
1. Consultant for Pediatricians May 2006