Cat Scratch Disease is a human disease characterized by a painful regional lymphadenitis usually proceeded by a cat scratch. About 25,000 cases of Cat Scratch Disease are diagnosed in the United States every year. The causative agent of Cat Scratch Disease is Bartonella henselae, a bacteria that attaches to or enters the red blood cells of infected individuals.

Fleas transmit the bacteria between cats. The likely means of transmission of Bartonella from cats to humans is the inoculation of flea feces containing Bartonella through a contaminated cat scratch wound or across a mucosal surface. Humans who are immunocompromised for any reason are at greater risk of developing disease, and often have more serious disease than those with an uncompromised immune system.

The incidence of infection in cats is not known, but may be as high as 50% of healthy cats in flea endemic areas. Most infected cats are less than two years old. The majority of infected cats show only mild symptoms of disease or none at all. An infected cat may experience a short period of fever, anorexia, lethargy, and enlarged lymph nodes. Most of the time Cat Scratch Disease in humans produces only mild, self-limiting symptoms of fever and benign lymphadenopathy. However, more serious diseases such as bacillary angiomatosis, endocarditis, central nervous system disorders, and prolonged or relapsing fever can result from infection with Bartonella. Diagnosis of the infection in cats can be difficult due to the small number of organisms present and the cyclic nature of the organisms’ presence in the bloodstream.

There is no good treatment for feline Bartonella infection. No antibiotic has proven to clear the organism from a cat’s bloodstream, but treatment may reduce the numbers of bacteria present.

The most effective means of preventing transmission is to keep your cat free of flea infestation by using a monthly preventative. Behaviors that encourage cats to scratch or bite, such as aggressive play, should be avoided. Keeping cats' claws trimmed may help prevent transmission. Any scratches or bites should be immediately washed using soap and water, and consult a physician if necessary.