ANIMAL BITES

ANIMAL BITES - George R. Bergus, MD
BASICS
DESCRIPTION
• Bite wounds to humans from dogs, cats, other animals including humans
• System(s) Affected: Endocrine/Metabolic; Hemic/Lymphatic/Immunologic; Nervous; Skin/Exocrine
ALERT
Geriatric Considerations
• Serious injury from any bite wound is more common >50 years old, those with wounds in the upper extremities, or those with puncture wounds.
• Increased risk of infection >50 years old
Pediatric Considerations
Young children are more likely to have severe bites.
GENERAL PREVENTION
• Instruct children and adults about animal hazards.
• Educate dog owners about responsible dog ownership.
• Strongly enforce animal control laws.
EPIDEMIOLOGY
Incidence
• Dog bites: 1,200/100,000
• Cat bites: 160/100,000
• Snake bites: 15/100,000 nonvenomous bites and 3/100,000 venomous bites per year
• Lifetime prevalence for animal bite: 50,000/100,000
• Dog bites are responsible for 1/3 million emergency room visits per year
Prevalence
• Predominant age: All ages, but children more likely to be affected
• Predominant sex: Male > Female
RISK FACTORS
• Dog bites are more common during warm weather.
• Male dogs are more likely to bite.
• Clenched-fist injuries are frequently associated with the use of alcohol.
ETIOLOGY
• Most bite wounds are from a domestic pet known to the victim.
• Large dogs are the most common source of bite wounds.
• Human bites are often the result of one person striking another in the mouth with a clenched fist.


DIAGNOSIS
SIGNS AND SYMPTOMS
• Bite wounds can be tears, punctures, scratches, avulsions, or crush injuries.
• Dog bites (80-90% of bites)
- In adults, hands are most commonly affected.
- In children, the face is the most common site of injury, and involvement of the trunk is uncommon.
• Cat bites (10% of bites)
- Predominantly involve the hands, followed by lower extremities, face, and trunk
- Are more likely to become infected because of puncture nature of wounds
TESTS
Lab
• 85% of bite wounds will yield a positive culture, but culturing at time of injury is of little benefit
• Wound culture is essential in directing therapy.
- Some pathogens are slow growing, so cultures should be kept for 7-10 days
- Gram stain is sensitive but not specific for infecting organism
• Dog bites
- Pasteurella species is present in 50% of bites.
- Also found: Streptococcus viridans, Staphylococcus aureus, coagulase-negative Staphylococcus, Bacteroides, Capnocytophaga canimorsus, Fusobacterium
• Cat bites
- Pasteurella species is present in 75% of bites.
- The wound is often contaminated by other mixed bacteria, including several species of both aerobic and anaerobic organisms.
• Human bites
- Streptococcus species, Staphylococcus aureus, Eikenella corrodens, and various anaerobic bacteria are very common.
• Other animal bites
- Scant information on pathogens
• Drugs that may alter lab results
- Previous antibiotic therapy
Imaging
• If bite wound is near a bone or joint, a plain radiograph is needed to check for bone injury and to use for comparison later if osteomyelitis is suspected.
• In human bite wounds from clenched-fist injuries, order plain-film radiographs to check for metacarpal or phalanx fracture.
Diagnostic Procedures/Surgery
• Consider rabies prophylaxis for bats, nondomestic dogs; rarely skunks, foxes and raccoon
• Surgical exploration may be needed to ascertain extent of injuries.
• Exploration should be performed on all serious hand wounds, especially clenched-fist injuries involving a joint.
DIFFERENTIAL DIAGNOSIS
Diagnosis is straightforward; what is of concern is judging the risk to the patient from the injury and resulting infection.
TREATMENT
GENERAL MEASURES
• Appropriate health care: Outpatient, unless patient has fulminant infection requiring systemic antibiotics, close observation, or surgery
• Elevation of the injured extremity to prevent swelling
• Contact the local health department and consult about the prevalence of rabies in the species of animal involved.
MEDICATION (DRUGS)
First Line
• Consider antirabies therapy.
• Use tetanus toxoid in those previously immunized, but >5 years since their last dose.
• Consider tetanus immune globulin (TIG) in patients without a full primary series of immunizations.
• Prophylactic therapy if wound seen in 1st 12 hours
- Dog, cat, or animal: Amoxicillin-clavulanate 500-875 mg b.i.d. PO (pediatric: 20-40 mg/kg/d PO given t.i.d.)
- Snake bite: If venomous, the patient needs rapid transport to a facility capable of definitive evaluation. If an envenomation has occurred, the patient will need to receive antivenin unless envenomation was only minimal. Be sure patient is stable for transport; consider measuring and or treating coagulation and renal status along with any anaphylactic reactions before transport.
- Human bites: Amoxicillin-clavulanate (Augmentin) potassium, adult: 500 mg PO t.i.d. (pediatric: 20-40 mg/kg/d PO given t.i.d.)
• Established infection
- After patient has developed a clinical infection, amoxicillin-clavulanate potassium (Augmentin) can be used pending culture reports
• Contraindications: Do not use penicillin-derived antibiotics in those with penicillin allergy.
• Precautions: Prescribe dosage of antibiotics by body weight and renal function.
• Significant possible interactions: Antibiotics may decrease efficacy of oral contraceptives
Second Line
• Alternative therapy for penicillin-allergic patients (for prophylaxis or empiric treatment)
- ~10% cross-reactivity with cephalosporins in penicillin-allergic patients
- Dog bite: Moxifloxacin 400 mg/day  7 days in adults (pediatric: trimethoprim- sulfamethoxazole along with Clindamycin); avoid cephalexin due to resistant strains of Pasteurella multocida
- Cat bite: As for dog bite
- Human bite: Moxifloxacin 400 mg/day
• If hospitalized with established infection: Ampicillin-sulbactam (Unasyn) 1-2 g IV q6h or ticarcillin-clavulanate (Timentin) 3.1 g IV q4-6h
SURGERY
• Copious irrigation of the wound with normal saline via a catheter tip is needed to reduce risk of infection.
• Devitalized tissue needs debridement.
• Debridement of puncture wounds not advised.
• Consider surgical closure if the wound is clean after irrigation and bite is 12 hours old. Puncture wounds should be left open.
• Delayed primary closure in 3-5 days is an option for infected wounds.
• Splint hand if it is injured.
• Human bite wounds on the hands should not be primarily closed because of the high risk of infection. Large, gaping wounds should be reapproximated with widely spaced sutures or Steri-Strips.
FOLLOW-UP
PROGNOSIS
Wounds should steadily improve and close over by 7-10 days.
COMPLICATIONS
• Septic arthritis
• Osteomyelitis
• Extensive soft tissue injuries with scarring
• Sepsis
• Hemorrhage
• Death
• Gas gangrene can take an exceedingly rapid course and should be treated very aggressively.
PATIENT MONITORING
• Patient should be re-checked in 24-48 hours if not infected at time of 1st encounter
• Daily follow-up is warranted with active infections.
• If antibiotics are used for an active infection, the duration of therapy should be 7-14 days, depending on the severity of the infection and the clinical response.
REFERENCES
1. Stevens DL, et al. Practice guidelines for the diagnosis and management of skin and soft-tissue infections. Clin Infect Dis. 2005;41(10):1373-1406.
2. Fleisher GR. The management of bite wounds. N Engl J Med. 1999:340:138-140.
3. Griego RD, et al. Dog, cat and human bites: A review. J Am Acad Dermatol. 1995;33: 1019-1029.
4. Presutti RJ. Prevention and treatment of dog bites. Am Fam Physician. 2001;63(8):1567-1572, 1573-1574.
5. Sacks JJ, et al. Fatal dog attacks 1989-1994. Pediatrics. 1996;97:891-895.
MISCELLANEOUS
Rabies
• Contact your local health department for information about the risk of rabies.
• Most human rabies are related to bat bites. See also: Bartonella Infections; Cellulitis; Rabies; Snake Envenomations; Crotalidae; Elapidae