For almost 100 years, cat scratches have been associated with illness in people.

Cat Scratch Disease (CSD) is also called Cat Scratch Fever and benign lymphoreticulosis. While CSD is found all over the world, it is an uncommon disease.

One estimate by the Centers for Disease Control found that there were 2.5 cases of CSD per 100,000 people per year in the United States. While multiple cases of CSD in one household can occur, this situation is rare. A study in Florida found that more than one member of a family contracted CSD only 3.5% of the time. The majority of individuals who contract CSD are under the age of 17, and are usually under the age of 12.

Typically, a small skin lesion (resembling an insect bite) develops at the site of a cat scratch or (less commonly) a bite, followed within two weeks by swollen lymph nodes and sometimes a fever.

The illness is mild and self-limiting in the majority of patients, although it may take some months for the swollen lymph nodes to return to normal. Treatment is usually not required.

Reports over the last few years, however, have extended the spectrum of problems associated with CSD to include such things as tonsillitis, encephalitis, hepatitis, pneumonia and other serious illnesses in a very small number of cases. People with compromised immune systems, such as AIDS and cancer patients, are most at risk and can become most seriously ill.

Diagnosis of CSD may not be easy. There is no simple diagnostic test. Most physicians rely on history of exposure to a cat , the presence of typical clinical signs, failure to find another cause, and examination of tissues, such as biopsy of a swollen lymph node. Other diseases, such as tuberculosis, brucellosis, and lymphoma, can cause similar symptoms.

Over the years, the cause of CSD had remained elusive, although bacteria were commonly suspected to be the culprit. In 1988, a bacterium called Afipia felis was cultured from the lymph nodes of patients with CSD. In recent years, many studies have implicated the gram negative bacterium Bartonella henselae as the primary (but not the sole) cause of CSD. B. henselae is related to the agent of Trench Fever, B. quintana, a disease common in the trenches of World War I. Other Bartonella species may also be involved in CSD.