From the Center for Disease Control and Prevention (CDC)

Many species of Capnocytophaga bacteria live in the mouths of dogs and cats. These bacteria do not make dogs or cats sick.

Rarely, Capnocytophaga species can spread to humans through bites, scratches, or close contact from a dog or cat and cause illness. Most people who have contact with a dog or cat do not become sick. People with a weakened immune systems who have difficulty fighting off infections (for example, people with cancer or those taking certain medications such as steroids) are at greater risk of becoming ill.

How Do I Get Infected?

Many Capnocytophaga species are considered normal oral flora (bacteria commonly found in the mouths) of humans, dogs, and cats. These bacteria cause opportunistic infections, which means they have to have the right conditions to cause an infection, such as in a person with a weakened immune system. People with weakened immune systems include, for example, those who drink alcohol excessively, who have had their spleens removed, and who have HIV infection or cancer. People with these conditions should speak with their doctors about how to safely interact with cats and dogs.

The Capnocytophaga species that are common in dogs and cats can be spread to people through a bite or after close contact with dogs or cats. Infections are more often linked to dog bites or dog contact.

In fact, up to 74% of dogs have Capnocytophaga species detected in their mouths, compared with up to 57% of cats.

See the Preventing Dog Bites page for information on how to prevent dog bites and what to do if you are bitten, regardless of your health status.

Other Capnocytophaga species can also be found in human mouths and can cause illness in some people. When the illness is caused by the bacteria within one’s own mouth, it’s called an endogenous infection. People who have weak immune systems get endogenous infections more often than healthy people. Most reported infections occur in tissues connected to the mouth and throat, including:

  • Periodontal (gum) disease
  • Respiratory tract infections
  • Eye infections

In both infections—those that spread from animals or from oneself—the bacteria can enter the blood stream, which can lead to infection in various parts of the body. Infection can also cause the following:

  • Septicemia (blood infection)
  • Endocarditis (inflammation of the lining of the heart)
  • Abscesses (collections of pus in the tissue that cause redness and swelling) in various body tissues

Inflammation of the eye, face, lymph nodes, or brain membranes

Signs and symptoms

People who are infected with Capnocytophaga experience a range of signs and symptoms such as:

  • Blisters around the bite wound within hours of the bite
  • Redness, swelling, draining pus, or pain at the bite wound
  • Fever
  • Diarrhea and/or stomach pain
  • Vomiting
  • Headache and/or confusion
  • Muscle or joint pain

After being bitten, most people who become ill will show symptoms within 3 to 5 days, but this can range anywhere from 1 to 14 days.

Although infections are usually associated with dog or cat bites, some people who develop a Capnocytophaga infection have not been bitten. People may be infected after close contact with a dog or cat, especially after contact with the animal’s saliva (spit).

There can be long-term side effects from infection, including amputation from gangrene, heart attack, and kidney failure.

About 3 in 10 people who get infected die. Some infections can lead to death within 24 to 72 hours after symptoms start.

If you have been bitten by a dog or cat, call your doctor right away, even if you don’t feel sick.

Risk of infection

People with certain health conditions are at greater risk of infection, but anyone could become sick from Capnocytophaga bacteria.

Risk factors include:

  • Excessive alcohol use
  • Not having a spleen
  • Immuno-compromising conditions, including but not limited to:
  • Cancer
  • Diabetes
  • HIV infection
  • Taking drugs that are toxic to cells (such as chemotherapy)

The majority of infections occur in adults over 40 years of age.

Capnocytophaga can cause serious illness in pregnant women and their fetuses. Infection during the last few weeks of pregnancy can lead to chorioamnionitis (inflammation of the membranes that surround the fetus), and sepsis (bacterial infection in the bloodstream or body tissues) in the newborn. Infection has also been linked to low birth weight.

If you have any of these conditions and have contact with dogs or cats, see the Prevention and Pets pages for more information. If you are bitten by a dog or cat, call your doctor immediately and describe your animal contact.


See the Preventing Dog Bites page to learn how to prevent bites, and what to do in case you are bitten by a dog or cat. If you are in a higher risk group, it is important to seek medical care promptly.

If you start having symptoms within 14 days of being bitten, get medical care immediately. Tell your health care provider that you were recently bitten by an animal. About 30% of people who get infected die. Some infections can lead to death within 24 to 72 hours after symptoms start.

If you have been bitten by a dog or cat, call your doctor right away, even if you don’t feel sick.

People may be infected after close contact with a dog or cat without being bitten. If you are at higher risk of infection, speak with your doctor about how to protect yourself when you have contact with pets. Also, see the Pets page for information about safer contact with pets.