What Is Cat Scratch Disease?

Medical Author: Melissa Stoppler, MD
Medical Editor: Barbara K. Hecht, PhD

Cat scratch disease is an infection caused by bacteria known as Bartonella henselae. Although about 40% of cats carry the bacteria in their saliva at some point in their lives, cats that carry Bartonella henselae do not themselves show any signs of illness. Most people contract the disease after being scratched or bitten by a cat.

Since these bacteria may also be present on cat fur, it is possible to contract the disease from petting a cat and then rubbing your eyes. Kittens are more likely than older cats to carry the bacteria and to transmit the infection to humans. Sometimes people who get cat scratch disease do not recall ever being scratched or bitten by a cat.

In people who have a normal immune system, cat scratch disease is usually not a serious illness. A small papule (a little raised lump) develops at the site of injury within 10 days. The signs and symptoms that follow may include:

As the disease progresses, more nodules may develop under the skin at the point of injury.

Most cases of cat scratch disease are self-limited, meaning that they resolve on their on without specific treatment. That usually happens within a few weeks. If the lymph nodes remain persistently inflamed or if the illness is very severe, your doctor may prescribe antibiotics. Antibiotics are given until the skin lesions resolve, usually three to four weeks.

Bartonella henselae can cause a more serious illness in people with an impaired immune system such as from HIV/AIDS or from chemotherapy for cancer. In people with HIV/AIDS, the infection can lead to an abnormal growth of blood vessels that form tumor-like masses, a condition called bacillary angiomatosis. This condition can cause severe inflammation of multiple organs including the brain, spleen, liver, lungs, and bone marrow. Untreated, the disease can be fatal in people with HIV/AIDS.

The best way to prevent cat scratch disease is to avoid situations in which you might be bitten or scratched by a cat. Don't play roughly with a cat, and don't force your attentions on a cat who clearly does not welcome them.

In any case, wash your hands thoroughly after playing with a cat. If you are bitten or scratched, wash the affected area well with soap and water. Cats should never be allowed to lick open sores or scratches on your skin.

It is not known exactly how cats acquire the infection. Since Bartonella henselae has been found in fleas, many experts believe that cats get the bacteria from fleas. Controlling fleas is also recommended as a way to help prevent infection.

If you are bitten or scratched by a cat and then develop any symptoms of cat scratch disease, contact your doctor immediately.

Last Editorial Review: 10/11/2007