Nearly 3 in 4 Dogs' Mouths Contain Potentially Deadly Bacteria, Should You Be Concerned?

capnocytophaga infection

Story at-a-glance -

  • Two recent very serious cases of human infections caused by bacteria found in dog and cat saliva has pet parents concerned
  • The bacteria is capnocytophaga canimorsus, which is normal oral flora present in the mouths of most dogs and cats
  • Despite wide news coverage, this type of infection is extremely rare; pet parents should be aware and take common sense precautions, but there’s no need to panic or overreact
  • It’s important to avoid animal bites, prevent pets from licking broken skin or open wounds, and seek immediate medical attention if the site of a bite or lick becomes red, puffy or painful

By Dr. Karen Shaw Becker

Some of you may have recently heard about a dog bite-related bacteria that caused the death of one person in Wisconsin and serious injury to another. The news coverage was wide and the gruesome details were disturbing, to say the least. According to USA Today:

“The bacteria led to the June 23 death of Sharon Larson, 58, a South Milwaukee woman and the June amputation of the hands and parts of the legs of Greg Manteufel, 48, of West Bend. In 2015, 3-year-old Liam Young of Louisburg had to have his fingers and toes amputated after he developed the same kind of infection.”1

The bacteria species is capnocytophaga (pronounced cap-no-sa-TOE-faga) canimorsus, which is present in the saliva of dogs and cats. According to the Centers for Disease Control (CDC), up to 74 percent of dogs and 57 percent of kitties have capnocytophaga in their mouths.2

Capnocytophaga Infections Are Exceedingly Rare

The devastating effect of the infections in Wisconsin is horrific to contemplate, which is why it’s also important to understand that such infections are extremely rare.

The CDC doesn’t track the number of cases of capnocytophaga infections, but is confident illness from the bacteria is rare. While not every infection is reported to the CDC, the agency is able to look at a database called MicrobeNet to get a general idea of the prevalence of the bacteria across the U.S. In the last year, the database received only 12 reports of capnocytophaga infections from doctors and hospitals around the country.

“There are so many dogs and so many people and interactions with dogs, that tells you how rare this is," CDC veterinarian Jennifer McQuiston and one the nation’s leading experts on capnocytophaga told USA Today. "Pets play a really important part of human existence. The answer is not to get rid of your pet or test your dog.”

How Humans Get Infected and People at Highest Risk

Capnocytophaga is considered normal oral flora. Unfortunately, capnocytophaga canimorsus, which is commonly found in the saliva of dogs and cats, has the potential to cause serious infection when it’s transmitted to a human. For a variety of reasons, it’s not practical to test pets for the bacteria.

For example, the bacteria might be present in saliva on Monday, but not on Tuesday. In addition, since it’s part of the normal oral microbiome of the majority of dogs and cats, it’s counterproductive to try to eliminate it with drugs like antibiotics.

Humans typically contract capnocytophaga from a dog bite. However, some people become infected without a bite, when a pet carrying the bacteria licks them. The saliva from the lick comes in contact with a mucous membrane or a cut, scrape or other opening on the skin.

According to the CDC, while anyone can become infected from the capnocytophaga bacteria, people with certain health conditions are at greater risk. These include:

  • Excessive alcohol use
  • Not having a spleen
  • Immunocompromising conditions, including but not limited to cancer, diabetes and HIV infection
  • Taking drugs that are toxic to cells (such as chemotherapy)

The majority of infections occur in adults over 40 years of age, and the bacteria can cause serious illness in pregnant women and their fetuses.

Signs of Possible Infection

Symptoms of infection with capnocytophaga bacteria can include:



Swelling or pus at the bite site




Stomach pain

Muscle or joint pain

As the infection progresses, there can be gangrene requiring amputation, sepsis, organ failure and death. According to the CDC, about 30 percent of people who acquire a capnocytophaga infection die.3 The high fatality rate is due in part to the speed at which the infection turns healthy people into very sick people.

Another problem is that early symptoms of this infection are common in many other illnesses, so neither patients nor their doctors are likely to immediately suspect capnocytophaga.

Awareness Is Important, but Overreacting Is Counterproductive

It’s important to realize that news reports like those detailing the capnocytophaga infections in Wisconsin tend to get a lot of attention and widespread circulation. In this case, the stories involve a scary infection that humans can acquire from their canine best friends, which is enough to give any dog lover pause.

But again — capnocytophaga infections are incredibly rare, so please don’t panic or overreact. It’s conceivable the infection isn’t as dangerous as the fatality rate would suggest, because there could be many people out there who get a mild infection and recover, never identifying the cause of their illness.

Your best bet is to simply be aware that the bacteria exists in the mouths of most dogs and cats, and take proper precautions, especially if you or a member of your household is at increased risk. Obviously, it’s always a good idea to avoid animal bites, and it’s also smart to prevent your pet from licking broken skin or open wounds.

If you’ve been bitten by a dog or cat, the CDC recommends that you call your doctor right away, even if you don’t feel sick. Wash the wound immediately and thoroughly with soap and water. If the bite site becomes red, swells or gets puffy, is painful or there’s a discharge, seek medical help right away. Some infections can lead to death within 24 to 72 hours after symptoms start.

If you start having symptoms within 14 days of a bite, again, seek immediate medical, care and tell your doctor you were recently bitten by an animal. The CDC’s McQuiston has pets, believes the risk of capnocytophaga is not a major concern for most people and also believes the benefits of having animal companions far outweigh the risks of any kind of animal-borne illness.

“I think pets are really important parts of many of our lives,” says McQuiston in an interview with Huffpost, “and they bring us really positive health benefits in addition to companionship.”4