What causes cat scratch disease?

Bartonella henselae is a bacteria that causes cat scratch disease.  It is found in the blood stream of healthy cats, especially kittens less than 6 months old.  The bacteria is transmitted when a cat scratches or bites the skin of a human.  The symptoms of cat scratch disease occur 1 to 4 weeks after contact with the cat.  Sometimes an affected child can not recall exposure to a cat and this has led some to believe that there may be other unknown ways to become infected.

What are the symptoms of cat scratch disease?

The most common presenting sign of cat scratch disease is a large, swollen lymph node.  The lymph node appears as a tender, moveable, "marble-like" object under the skin of the neck, in front of the ear, under the chin, in the arm pit, or leg crease.  There is often only one large lymph node, which may be as large as a golf ball!  There may be several lymph nodes in a group.

The site of the original scratch may also have a small, red bump or a line of bumps (due to a linear cat scratch).  These bumps are not always found.

Other symptoms are less common, including: mild fever, fatigue, and headache.

Some cases of cat scratch disease may affect the eye, causing redness and swelling (i.e., occuloglandular syndrome).  This probably occurs when a child plays with a cat and then rubs her eyes.  The lymph nodes in front of the ear on the same side as the affected eye are typically swollen.

How is cat scratch disease diagnosed?

A doctor may make the diagnosis based on the history of cat exposure, a characteristic bump at the scratch site, and the large, swollen lymph node on the same side as the scratch.

Blood tests are available to determine if antibodies to Bartonella henselae are present in the blood stream.  If present, infection is likely.

If the tests are negative, other causes of swollen lymph nodes should be considered.

How is cat scratch disease treated?

Most cases of cat scratch disease will resolve without treatment.  There is little evidence that antibiotics shorten recovery time.  When antibiotics are used, azithromycin, septra, ciprofloxicin, or clarithromycin are often used.

When a swollen lymph node is large and painful, the lesion may need to be drained with a needle.

The swollen lymph node may last for several months (and sometimes a year) before returning to a normal size.

How can cat scratch disease be prevented?

Avoidance of cats is probably the most effective avoidance measure.  This may be difficult for cat owners.  Fortunately the disease is mild and can not be transmitted from person to person.

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