I would like to know what exactly is "cat-scratch fever". I would also like to know how serious it is. Why do children get it? Do all cats have the potential to give it to them? Is it the same as germs in a paper cut?

The uncovering of the cause of cat-scratch fever (now called cat-scratch disease) has been one of the great mystery stories of modern medicine. The hallmarks of cat-scratch disease are enlarged, tender lymph nodes (especially in the armpit) found under toughened, warm, red skin. For centuries children have often had these symptoms with no known cause. For centuries children have played with cats and been scratched, but no connection was made.

In 1946, a Dr. Hanger in New York, the owner of a "ferocious tiger," got what appeared to be an infected hangnail and then a swollen, tender lymph node full of pus under his collarbone. His friend, Dr. Rose, drained the pus from the lymph node -- but to their surprise, the pus was found to be sterile (containing no germs). They re-injected Dr. Hanger with some of this material, under the skin of his arm, and he had a strong skin reaction (sort of like a TB skin test, but this was a tiger-claw skin test).

Then, across the Atlantic in 1950 Paris, a 6-year-old French boy was observed to have a swollen, tender lymph node near the site of a scratch from a house cat. His physician, Dr. Debre, obtained some of the Hanger/Rose material (which he actually got from the University of Cincinnati, where microbiologists were now trying to figure out this stuff). He injected some of the material under the Parisian boy's skin, and the boy developed a positive skin-test reaction!

This was the first documented case of what they called "La maladie des griffes de chat." Over the next several years the international collaboration continued, and cat-scratch fever was defined as a specific disease. A positive skin test in someone with swollen lymph nodes, who had been exposed to a cat, was considered to make the diagnosis.

When I entered medical school, cat-scratch disease was still a mystery. We knew that it happened after cat scratches, and it seemed that it must be caused by some type of bacteria, but no bacteria had ever been found in those swollen lymph nodes. Then, while I was in my second year of medical school, very tiny proteobacteria were seen in early cat-scratch lymph nodes that had been stained with silver. An organism had been found!

But what was it? Many possible identities were proposed and then disproved. When I was a pediatric intern, someone was finally able to grow the bacteria. The definitive pediatric infectious disease textbook (Feigin and Cherry -- a wonderful book) announced in the 1992 edition: "The bacterium that causes cat-scratch disease has been conclusively identified over the past decade...Afipia felis."

I received my copy of the next edition of Feigin and Cherry in today's mail. It says, "further study has now discredited Afipia felis as the cause of cat-scratch disease!" Even as the previous edition was going to press, new DNA diagnostic techniques applied to cat-scratch disease in AIDS patients were providing a wealth of new information.