Bartonella henselae is a Gram-negative bacterium found inside cells. It is the most frequent cause of cat-scratch disease. B. henselae is transmitted by fleas and ticks which feed on the blood of infected mammals (humans, cats and dogs). There is a risk of a direct infection in the case of a bite or scratch by a sick animal.

B. henselae attacks macrophages, erythrocytes and vascular endothelial cells causing their lysis. The most frequent symptom of the infection is a papule (pustule) at the bite site. After some time, nearby lymph nodes will swell. This may be accompanied by flu-like symptoms (fever, muscle and joint pain, shivering and fatigue); however, in the overwhelming majority of cases, the disease is asymptomatic. The disease constitutes a hazard for immunodeficient humans and animals.