Cat-scratch disease is an infection caused by the bacteria Bartonella henselae.

What is going on in the body?

The Bartonella henselae bacteria causes a local infection at the site where it entered the body. Lymph nodes near the area become swollen 1 to 7 weeks after exposure to the bacteria. Sometimes, a small, solid skin lesion will develop at the site. Most cases of cat- scratch disease are self-limited, which means they go away on their own.

In rare cases, cat-scratch disease can cause infections in other body areas, such as the following:

People with impaired immune systems are more likely to suffer severe and complicated infections. This includes people with immunodeficiency disorders, such as HIV. People who are being treated with chemotherapy or radiation therapy for cancer are also at higher risk.

What are the causes and risks of the infection?

Bartonella henselae bacteria cause cat-scratch disease. They are transmitted by contact with the saliva of a cat. An individual can become infected from a cat bite or scratch, or even from petting the cat. The saliva is found on the cat's fur and paws after the cat grooms itself. The cat itself is usually healthy. Young cats are the most common source of infection for humans.

Cat-scratch disease is most common in children and adolescents. It is seen most often in late summer, fall, and early winter.