There is no accurate data about the number of animal bites that occur each year other than emergency-room visits (approximately 320,000 a year). There are 70 million pet dogs and 74 million pet cats in the U.S., and there are an estimated three to six million animal bites per year, approximately 80 to 90% are from dogs, five to 15% are from cats, and two to five percent are from rodents, with the balance from other small animals (e.g. rabbits, ferrets), farm animals, monkeys, reptiles and others.

Treatment depends on the type of animal, location of the bite and the potential of rabies. In this article, we will discuss the initial first aid at home and needed follow-up with a physician for the most common types of bites. We will also discuss indications for rabies vaccinations.

Common causes of wound infections

Bites from dogs and other larger mammals are characterized by crushed tissue because of the round teeth and strong jaws. Dogs can exert from 200 to 450 pounds per square inch of pressure depending on the size of the animal. Besides lacerating the skin, deeper tissues such as bones, nerves, blood vessels, tendons and muscle can also be damaged. This differs from cats, because their sharp pointed teeth cause puncture wounds and lacerations that may introduce bacteria deep into tissues.

The location of the bite is also important in terms of developing infection. Bites to the hands have a very high incidence of infection. Common bacterial contamination from dog bites includes Staphylococcus, Streptococcus, Pateurella, Bacteroides and others.

Most infections from a cat bite involve Pasteurella, Actinomyces (fungus) and Bacteroides. Infections caused by cat bites generally develop faster than those from dogs. Unprovoked bites by wild or sick-appearing animals (most notably by dogs, cats, raccoons, foxes, skunks and bats) raise concerns about likelihood of rabies exposure.

Local soft tissue infection and cellulitis are the most common complications of an animal bite. Blood and joint infections are the most serious, especially in immune-compromised persons. Pasteurella infections also may be complicated by sepsis. meningitis, osteomyelitis (bone infection), abscesses, pneumonia, endocarditis and septic arthritis are additional concerns.

First Aid Care of an animal bite

After a bite has occurred, it is important first to wash the wound with soap and water. You can use an antibiotic cream if it involves a small area without extensive tissue damage. If there is excessive bleeding, put gentle pressure on the area. Cover the wound area with a clean cloth, and then seek treatment from your doctor or at an emergency room.

Follow-up care of an animal bite

Most serious bite wounds are treated in the emergency room because of the concern for rabies. The treating physician will do the following:

Wounds are carefully inspected for deep injury and crushed tissue. This may require local anesthesia because it is painful to probe wounds.

The wound is then irrigated with sterile water or a salt solution to remove dirt and blood clots. In some cases the doctor has to trim out crushed tissue. This is important because it significantly decreases the chance of infection, including rabies.

Closing of an open wound is considered in bite wounds that can be effectively cleansed. A decision to keep the wound open or to delay closing for more than eight to 12 hours may be made in the case of bite wounds to the hands and lower extremities or in people with decreased immunity. This usually involves consultation with a plastic surgeon to determine the best way to reduce scarring if the bite area is large.

It may be difficult to irrigate small puncture wounds, especially those inflicted by the teeth of a cat. Because of the higher rate of infection, the wound may be extended with scalpel so that the area can be irrigated and left open to heal.

Facial wounds have a low risk of infection even when closed due to an increased blood supply to the head and neck. To reduce facial scaring, facial wounds are usually closed along with giving an antibiotic.

A tetanus booster is recommended, and everyone is assessed for rabies prophylaxis. Anti-rabies treatment is indicated for bites by dogs and cats whose rabies status cannot be determined, or in foxes, bats, raccoons or skunks.

The choice of antibiotics is determined by the type of animal bite and whether there are any drug allergies for the person. The most commonly recommended antibiotic prescribed is amoxicillin-clavulanate for dog, cat and human bites. There are a number of other antibiotics that can be prescribed prophylactically, if needed. For monkey bites, an antiviral antibiotic is prescribed.

Rabies Treatment

If rabies protection is required, a series of injections is given. For individuals not previously given rabies vaccine, a dose of human rabies immune globulin is given along with a series of rabies vaccine on day 0, 3, 7 and 14, post bite. These injections are given in the shoulder. If a person has previously received vaccinations only two doses of vaccine (on the day of exposure and then three days later) are needed.

There can be mild, local reactions to the rabies vaccine, such as pain, redness, swelling, or itching at the injection site. For some individuals, headache, nausea, abdominal pain, muscle aches and dizziness have been reported. Local pain and low-grade fever may follow injection of rabies immune globulin.