Mammalian Bites

[Section Outline]

Each year, there are ∼300 dog and cat bites per 100,000 population in the United States, with most bites inflicted by pet animals.
The microbiology of bite wounds typically reflects the oral flora of the biting animal.
Bites from many different animals can transmit rabies and tularemia.

Dog Bites

Epidemiology: Dogs bite ≥4.7 million people per year, causing 80% of all animal bites; 15-20% of dog bites become infected.
Bacteriology (Table 29-1 Management of Wound Infections Following Animal and Human Bites): Includes aerobic and anaerobic organisms, such asβ-hemolytic streptococci; Eikenella corrodens; Capnocytophaga canimorsus; and Pasteurella, Staphylococcus, Actinomyces, Prevotella, Neisseria, and Fusobacterium species.
Clinical features: Typically manifest within 8-24 h after the bite as local cellulitis with purulent, sometimes foul-smelling discharge. Systemic spread (e.g., bacteremia, endocarditis, brain abscess) can occur. C. canimorsus infection can present as sepsis syndrome, disseminated intravascular coagulation (DIC), and renal failure, particularly in pts who are splenectomized, have hepatic dysfunction, or are otherwise immunosuppressed.

Cat Bites

Epidemiology: Cat bites and scratches result in infection in >50% of cases.
Bacteriology (Table 29-1 Management of Wound Infections Following Animal and Human Bites): Includes organisms similar to those involved in dog bites. Pasteurella multocida and Bartonella henselae (the agent of cat-scratch disease) are important cat-associated pathogens. Tularemia and sporotrichosis have been associated with cat bites.
Clinical features:P. multocida infections can cause rapidly advancing inflammation and purulent discharge within a few hours after the bite. Because of deep tissue penetration by narrow, sharp feline incisors, cat bites are more likely than dog bites to cause septic arthritis or osteomyelitis.

Other Nonhuman Mammalian Bites

Old World monkeys (Macaca species): Bites may transmit herpes B virus (Herpesvirus simiae), which can cause CNS infections with high mortality rates.
Seals, walruses, polar bears: Bites may cause a chronic suppurative infection known as seal finger, which is probably due to Mycoplasma species.
Small rodents and their predators: Bites may transmit rat-bite fever, caused by Streptobacillus moniliformis (in the United States) or Spirillum minor (in Asia).
- Rat-bite fever occurs after the initial wound has healed, a feature distinguishing it from an acute bite-wound infection.
- S. moniliformis infections manifest 3-10 days after the bite as fever, chills, myalgias, headache, and severe migratory arthralgias followed by a maculopapular rash involving the palms and soles. Disease can progress to metastatic abscesses, endocarditis, meningitis, and pneumonia.
Haverhill fever is an S. moniliformis infection acquired from contaminated milk or drinking water and has manifestations similar to those described earlier.
- S. minor infections cause local pain, purple swelling at the bite site, and associated lymphangitis and regional lymphadenopathy 1-4 weeks after the bite, with evolution into a nonspecific systemic illness.

Human Bites

Epidemiology: Human bites become infected 10-15% of the time.
- Occlusional injuries are inflicted by actual biting; clenched-fist injuries result when the fist of one individual strikes the teeth of another.
- Clenched-fist injuries are more common and typically result in more serious infections (e.g., septic arthritis, tenosynovitis).
Bacteriology: See Table 29-1 Management of Wound Infections Following Animal and Human Bites.

TREATMENT
Mammalian Bites Wound management: Wound closure is controversial in bite injuries. After thorough cleansing, facial wounds <24 h old are usually sutured for cosmetic reasons and because the abundant facial blood supply lessens the risk of infection. Elsewhere on the body, many authorities do not attempt primary closure of wounds that are or may become infected (e.g., wounds >12 h old), preferring instead to irrigate them copiously, debride devitalized tissue, remove foreign bodies, and approximate the margins. Delayed primary closure may be undertaken after the risk of infection has passed. Puncture wounds due to cat bites should be left unsutured because of the high rate at which they become infected. Antibiotic therapy: See Table 29-1 Management of Wound Infections Following Animal and Human Bites. Antibiotics are typically given for 3-5 days (as prophylaxis in pts presenting within 8 h of the bite) or for 10-14 days (as treatment for established infections). Other prophylaxis: Rabies prophylaxis (passive immunization with rabies immune globulin and active immunization with rabies vaccine) should be given in consultation with local and regional public health authorities. A tetanus booster for pts immunized previously but not boosted within 5 years should be considered, as should primary immunization and tetanus immune globulin administration for pts not previously immunized against tetanus.