I’ve always heard that dogs’ mouths are cleaner than humans. Is this true?
Neither dogs nor cats nor humans have mouths that can even remotely be considered clean. All are filled with bacteria, many of which can cause disease if they enter broken skin. Over 130 disease-causing microbes have been isolated from dog and cat bite wounds.¹ Animals’ saliva is also heavily contaminated with bacteria, so a bite may not even be necessary to cause infection; if you have a cut or scratch and allow a pet to lick it, you could be setting yourself up for trouble.

What are the particular dangers from animal bites?
Bites to the hand, whether from cats or dogs, are potentially dangerous because of the structure of the hand. There are many bones, tendons, and joints in the hand and there is less blood circulation in these areas. This makes it harder for the body to fight infection in the hand. Infections that develop in the hand may lead to severe complications, such as osteomyelitis or septic arthritis.

In small children, bites to the face, neck, or head are extremely hazardous. Because their small stature often puts their heads near dogs’ mouths, children are often bitten in these areas. Dog bites can cause fractures of the face and skull and lead to brain and nervous system infections. Dog bites cause, on average, about 15-20 fatalities a year in the United States. Most of these victims are infants and young children.

Which is worse, dog bites or cat bites?
Dogs have strong jaws—large dogs can exert more than 450 pounds of pressure per square inch—and their teeth are relatively dull. So the wounds caused by dogs are usually crushing of the tissue bitten and lacerations or tearing of the skin rather than puncture wounds. Most dog bites do not penetrate deeply enough to get bacteria into bones, tendons, or joints, but they often do a lot of damage just from the trauma of the bite. Tissue that has been crushed, however, such as may occur with a bite to the hand, is particularly susceptible to infection.

Cats’ teeth are thin and sharp, so the wounds they cause are more likely to be puncture wounds. These wounds can reach into joints and bones and introduce bacteria deeply into the tissue. Puncture wounds are very difficult to clean, so a lot of bacteria may be left in the wound. Also, most cat bites are to the hand, which makes infection more likely.

Dog bites often do more outright damage, but only 3 to 18 percent become infected. In contrast, cat bites may appear more trivial, but up to 80 percent of cat bites may become infected if proper care is not taken.

What kinds of infections can develop?
Many infection-causing bacteria have been isolated from dog and cat bite wounds. The four we discuss here are probably the most significant.

Pasteurellosis.
The most common bite-associated infection is caused by a bacterium called Pasteurella. Most cats and dogs—even healthy ones—naturally carry this organism in their mouths. When an animal bites a person (or another animal), these bacteria can enter the wound and start an infection. The first signs of pasteurellosis usually occur within 2 to 12 hours of the bite and include pain, reddening, and swelling of the area around the site of the bite. Pasteurellosis can progress quickly, spreading toward the body from the bitten area. It is important that you seek medical care immediately if these symptoms occur. Untreated, this infection can lead to severe complications. Bites to the hand need special attention; if pasteurellosis develops in the tissues of the hand, the bacteria can infect tendons or even bones and sometimes cause permanent damage if appropriate medical care is not administered promptly.

Streptococcal and Staphylococcal Infections.
These bacteria can cause infections similar to those caused by Pasteurella. Redness and painful swelling occur at or near the site of the bite and progress toward the body. As with pasteurellosis, you should seek prompt medical care if these symptoms develop.

Capnocytophaga Infection.
This is a very rare infection, but we mention it here because it is so dangerous if it develops. There is no common name for this infection, which is caused by the bacterium Capnocytophaga canimorsus. Most of the people who have become infected were bitten by dogs; in many instances the bite wounds themselves were tiny and would not have ordinarily called for any special medical care. But Capnocytophaga can cause septicemia, or blood poisoning, particularly in people whose immune systems are compromised by some underlying condition (see box below). Up to 30 percent of people who have developed this septicemia have died. People who have had their spleens removed are at special risk for this infection. Early symptoms may include nausea, headache, muscle aches, and tiny reddened patches on the skin.

If you have any of the risk factors listed below, particularly if you have had your spleen removed, it is very important that you take proper immediate care of any animal bite wound and promptly seek medical advice.