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.