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
Many infection-causing bacteria have been isolated from dog and cat bite
wounds. The four we discuss here are probably the most significant.
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.
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
How do I know if I am at risk for
Anyone who is bitten by a cat or a
dog and who does not take proper
care of the wound is at risk of
But some people are at increased
- Are you over 50 years of age?
- Do you have diabetes,
circulatory problems, liver
disease, alcoholism, or HIV/AIDS?
- Have you had a mastectomy or
- Are you taking chemotherapy or
- Have you had your spleen
If you answered “yes” to any
of these questions, you may be more
likely to develop a serious
infection than other people. You
should take special care to avoid
being bitten or scratched by any
I do if I am bitten?
Immediately and thoroughly wash the wound with
plenty of soap and warm water. The idea is to remove as
much dirt and saliva—and therefore, bacteria—as
possible. It may hurt to scrub a wound, but an infection
will hurt a lot more. Scrub it well and run water over
it for several minutes to make sure it is clean and all
soap is rinsed out. It is a good idea to follow the
washing with an antiseptic solution, such as iodine or
other disinfectant, but always wash with soap and water
first. Apply antibiotic ointment and cover the wound
with gauze or a bandage. If the wound is severe, or if
you have any of the risk factors listed above, seek
medical advice at once. Your doctor may want you to take
antibiotics to prevent infection from developing. If you
have not had a recent tetanus booster, you may be
advised to take one. And if you are bitten by a wild or
stray animal that could have rabies, you may need to
begin anti-rabies treatment. (See
You Should Know About Rabies Prevention).
If you have had your spleen removed, you should be
aware that the potential for fatal infection exists,
even from seemingly minor wounds. Some experts recommend
that people without spleens should completely avoid
contact with cats and dogs. This is an issue you and
your doctor should discuss in detail.
For most people, however, the benefits of companion
animals outweigh the risk. If you have any of the risk
factors shown in the box above, you should do everything
possible to avoid being bitten or scratched by dogs or
cats. If wounds do occur, you should clean them promptly
and thoroughly and seek medical advice. A little care
and common sense can go a long way in preventing
The information presented here is
not intended to take the place of
professional medical advice. If you are
bitten by any animal, always consult your
physician for his/her recommendations.
1Talan DA, Citron DM, Abrahamian FM, et
al, 1999. Bacteriologic analysis of infected dog and cat
bites. New England Journal of Medicine 340:85-92.