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.

image of a dog licking a young woman's face

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