When I was a child, I thought “Cat Scratch Fever” was something my grandmother made up to keep me from spending so much time playing with her cat. I was grown before I found out that it was a real disease.

Cat Scratch Fever was first recognized in 1931, but it is an oddball disease. It took a long time to find out that it had a bacterial cause, and even longer to identify the particular type of bacteria. Scientists now agree that the culprit is Bartonella henselae, a small (even by microscopic standards), fragile organism that lives inside the cells of its host. This is pretty much the only thing that is cut-and-dried about it. I am more confused about the condition now than when I first started to research it.

Apparently B. henselae is a fairly common infection in cats, although it seldom produces any illness in them. Some cats may experience a mild fever for a few days, and they may have some lymph node swelling and/or a mild anemia. Few owners would even take notice. There have been some recent reports of eye involvement. About 40% of cats are affected at some point in their lives and they can carry the bacteria in their blood for long periods.

B. henselae has also been found in fleas, and experimentally they can spread the infection from one cat to another. It is reasonable to assume that this also happens under natural conditions, but that has not been proven. A higher percentage of the cat population is infected in warmer climates where the flea population is larger. The disease can also be transmitted cat to cat by blood transfusions.

So how do people get Cat Scratch Fever? (Baby Boomers, I know what you're thinking-get those Ted Nugent lyrics out of your head!)

Most people who get the disease have been bitten or scratched by a kitten less than 6 months old. Outdoor cats are more likely to be affected than indoor pets. Two human populations are most often affected-children/young adults and veterinarians. (The two groups who don't know any better than to keep their hands away from an unhappy cat!) These make up 80-90% of human cases. Occasionally, people who have no known exposure to cats will develop the disease.

The exact mode of transmission is not understood. It may be that some “flea dirt,” which is actually dried, digested blood, may cling to a cat's claws after grooming, and this may be how it enters the human body when scratched by a cat. Cats also have the potential for this to be in their mouths after grooming. It stands to reason that outdoor cats would be more likely to have larger flea populations, and therefore more flea dirt present. Kittens would be less efficient at keeping their nails clean.

In humans, signs of the disease first appear as small pimples or pustules near the site of a cat scratch or bite, followed in about 1-4 weeks by swollen and tender lymph nodes, usually in the armpit. It is common to experience headache, fatigue, poor appetite, and sometimes a tonsillitis and neck pain. About 90% of cases resolve on their own, but the symptoms may linger for several months. Antibiotics will shorten the course of the disease.

Rarely, much more serious, even fatal, problems can develop. These complications are much more common in people with poor immune systems. Many cancer patients and organ transplant recipients are given therapies to suppress their immunity. People with HIV/AIDS are also at risk.

The Centers for Disease Control has the following recommendations to reduce your risk of contracting Cat Scratch Disease:

Avoid “rough play” with cats, especially kittens. This includes any activity that could lead to cat scratches and bites.

Wash cat bites and scratches immediately and thoroughly with running water and soap.

Do not allow cats to lick open wounds that you may have.

Control fleas.

If you develop an infection (with pus and pronounced swelling) where you have been scratched or bitten by a cat or develop symptoms, including fever, headache, swollen lymph nodes, and fatigue, contact your physician.