Bite Wounds

This discussion will focus on dog, cat and human bites.

Dog Bites

It is estimated that there are 4 million bites annually in the United States and about 80 percent of these are caused by dogs. Twenty percent of these dog bites will require medical attention due to concerns about infection, rabies, and cosmesis. In 85 percent of dog bites, the dog is owned by the victim's family, friend, or neighbour. There are about 20 deaths yearly in the U.S.A. due to a dog mauling. Serious maulings and bite-related fatalities are usually restricted to more powerful species such as pit bulls and rottweilers. Although most dogs never bite a human, any dog may, particularly when provoked. The majority of dog bites occurring in children are in the head and neck area, while dog bites to adults are mostly to the extremities. It is important to look for underlying fractures in head and hand bites sustained from dogs, as the pressure between the teeth can be up to 450 psi.

Cat Bites

Cat bites are responsible for 10 percent of mammalian bites. The victims tend to be older females. Whereas dog bites are more crushing in nature with ripping and avulsion of the soft tissue, cat bites are sharp puncture wounds. Due to the deep inoculum of bacteria from such a puncture, the risk of septic arthritis, suppurative tenosynovitis, and osteomyelitis of the hand is much higher with cat than with dog bites. The infection rate from a cat bite is up to 50 percent, and tends to present a few hours earlier than dog bites, likely due to their higher likelihood of carrying Pasteurella multocida.

Human Bites

Although human bites are less common than cat bites, they are more problematic and worrisome than any other type of mammalian bite. Human bites are either classified as "fight bites" or "occlusal bites". Fight bites occur on the hand when one punches someone in the mouth. The point of a tooth enters the victim's hand, often at the MCP joint level of the long, ring, or little finger. The inoculum may well be driven into the skin and underlying fat, through the extensor tendon, and into the joint capsule of the MCP joint. Often an accurate history is not obtained and may be deliberately altered by the victim due to embarrassment. Lacerations over the 3rd, 4th, and 5th metacarpals must be viewed as highly suspect for a human bite. Early exploration in the E.R. should include surgical extension of the wound proximally and distally and then moving the fingers into full flexion and extension to see the "path of the tooth" and to better determine if the extensor tendon or MCP joint is damaged. Untreated patients often present about 3 days later in exquisite pain with cellulitis, or worse, in the affected area. These wounds need to be opened, drained of pus, and likely taken to the Operating Theatre for exploration, debridement, and incision and drainage of the involved MCP joint. Usually such hands need to be admitted to hospital following surgery with elevation and appropriate antibiotics. X-rays should be performed to rule out an underlying bone injury, gas, or foreign body, such as a tooth fragment.

Occlusal human bites occur when one bites tissue directly, such as someone biting a piece of lip or ear. In general, completely detached fragments will not survive when reattached unless the injury occurs in a child (it may be worthwhile to try reattachment, however).

All Bites

Cultures from a mammalian bite are best taken at the time of infection to help direct antibiotic choices. If taken initially after a bite they tend to be nonspecific. Culture the specimen for both aerobes and anaerobes.

With all bite wounds it is important to know when the bite occurred. Infections that present within hours of a dog or cat bite tend to be caused from Pasteurella. It is important to ask of the species of animal that caused the bite, the animal's health and behaviour, vaccination status, observation availability, and whether the bite appeared to be provoked or not. It is important to know the patient's medication and allergy status and whether they are immunocompromised, particularly if they are suffering from diabetes or alcohol abuse.

Tetanus status must be ascertained and updated if necessary. All bites should be measured and described. Many cases go on to medical/legal activity and diagrams or photographs are often useful later. Good hand examinations, along with x-rays for dog bites, should be obtained. Bite wounds need to be copiously irrigated and then debrided with removal of any necrotic tissue. All but puncture wounds may benefit from debridement of the wound edges.

Bites to the hands should not be closed unless there is flap-like tissue from a dog bite that can be tacked down loosely following aforementioned care. Nonpuncture-type wounds to the face may possibly be closed loosely following irrigation and debridement, knowing the risk of subsequent infection is moderately high just the same. It is always feasible to perform a delayed primary closure 2 to 3 days post injury once the wound has better declared itself.

I tend to put all mammalian bites on antibiotics and, if being discharged home, I suggest close follow up in 1 to 2 days time.

Bacteriology of human bites is often complex and most bites are polymicrobial in nature. The most common organisms, however, remain staphylococcus aureus, various strains of streptococcus (both aerobic and anaerobic species), and bacteroides. As well, in 1/3 of human bites, Eikenella corrodens is encountered and in dog and cat bites one will see Pasteurella-induced infections. There is emerging antibiotic resistance amongst the staphylococcal and streptococcal species and drugs such as Clindamycin and Clavulin are now better choices against these organisms than Cloxacillin and Keflex.

Pasteurella and Eikenella, however, may be resistant to Clindamycin, and Clavulin is not effective against anaerobes, therefore combination therapy tends to be prescribed for mammalian bites.

First choice antibiotics are Clavulin plus Clindamycin or, if there is a pencillin allergy consider Cipro plus Clindamycin for adults or Septra plus Clindamycin for children. Antibiotic duration should be 5 to 7 days prophylactically and 10 to 14 days if an infection does occur. Most farm related bites can be treated in a similar fashion, although the risk of rabies is a bit higher.

Rabies

All mammalian bites should be assessed for risk of rabies, keeping in mind that 50,000 people in the world still die annually of this disease. There is usually one rabies death in Canada every 5 to 10 years. It is spread only through saliva, is universally fatal and has an incubation period of 3 to 8 weeks. Vaccinations include both an active regimen (5 inoculations over 1 month) along with a passive immune globulin given on day 0. The common carrying species vary throughout regions of North America. In Nova Scotia the rabies virus is carried only in a small percentage of brown bats, which in turn can expose other animals or humans through a bite. Keep in mind that it is possible to be bitten by a bat and not know it, nor see the bite wound. This is important if there is a history of finding a bat in a room where someone has been sleeping. A recommendation for post exposure prophylaxis towards rabies is given below.

Keep in mind that water-borne diseases tend to carry additional organisms such as Vibrio species which respond to Doxycycline. Later water-borne infections include various Mycobacterium species.

- Michael Brennan

Thanks to Dr. Mihkel Oja, Plastic Surgeon at the Dr. Everett Chalmers Hospital in Fredericton, New Brunswick for reviewing the draft copy of this article.