While a cat scratch may be the most common vehicle for transmitting CSD to people, the common cat flea is probably the vector for cats. The cat flea is a competent vector for Bartonella henselae, the organism that causes CSD, according to Jane Koehler, MD, of the University of California at San Francisco. Bacterium recently identified Cat scratch disease has been recognized since the 1950s but the bacterium that causes it, B. henselae has only recently been identified. The most common mode of transmission to humans is a scratch from an infected cat.
Infections apparently cause no harm to cats, and they display no symptoms.
Symptoms in humans begin with an inflammation around the scratch site, which progresses to swelling of the lymph nodes and a low-grade fever. B. henselae infection in people with weakened immune systems can lead to a potentially fatal disease called bacillary angiomatosis, which looks like Kaposi's sarcoma. Because so few HIV-infected people acquire this infection from their cats and cat ownership is so beneficial, we do not recommend giving up pet cats. In a study of bacillary angiomatosis patients published in the Journal of the American Medical Association in February 1994, Koehler and her colleagues identified the cat as the reservoir of B. henselae and determined the number of cats that were bacteremic. In the first experiment, Koehler and her colleagues evaluated the ability of the cat flea to transmit B. henselae by removing fleas from infected cats and transferring them to two uninfected kittens in a controlled environment that was free of fleas.