(See also Overview of Bartonella Infections.)
The domestic cat, particularly kittens, is a major reservoir for B. henselae. The prevalence of B. henselae antibodies in US cats is 14 to 50%.
About 99% of patients with cat-scratch disease report contact with cats, most of which are healthy. The specific location of the organism in the cat is unclear; however, periods of asymptomatic bacteremia occur in cycles. Infection is spread to humans via a bite or scratch. The cat flea transmits infection among cats and may be the cause of disease in humans who have not had contact with cats, although this theory is unproved. Children are most often affected.
Within 3 to 10 days after a bite or scratch, most patients with cat-scratch disease develop an erythematous, crusted papule (rarely, a pustule) at the scratch site. Regional lymphadenopathy develops within 2 weeks. The nodes are initially firm and tender, later becoming fluctuant, and may drain with fistula formation. Fever, malaise, headache, and anorexia may accompany lymphadenopathy.
Unusual manifestations occur in 11 to 12% of patients:
Patients may also present with a fever of unknown origin. B. henselae is one of the most common causes of culture-negative endocarditis, usually in patients with prior valvular heart disease. In immunosuppressed patients, B. henselae can cause bacillary angiomatosis and peliosis. Severe disseminated illness may occur in patients with AIDS.
Lymphadenopathy subsides spontaneously within 2 to 5 months. Complete recovery is usual, except in severe neurologic or hepatosplenic disease, which may be fatal or have residual effects.
Diagnosis of cat-scratch disease is typically confirmed by positive serum antibody titers (testing acute and convalescent sera 6 weeks apart is recommended) or PCR testing of samples from lymph node aspirates.
Because similar lymphadenopathy may be caused by other infections (eg, tularemia, mycobacterial infection, brucellosis, fungal infection, lymphogranuloma venereum), testing for those organisms may be done if the diagnosis is not clearly cat-scratch disease.
Lymph node biopsy may be done if cancer is suspected or if the diagnosis of cat-scratch disease needs to be confirmed. Diagnosis is suggested by characteristic histopathologic findings (eg, suppurative granulomas) or detection of organisms by immunofluorescence.
Immunocompromised patients and patients with systemic symptoms should also have blood cultures (which require prolonged incubation). Lymph node aspirates are rarely culture-positive. However, Bartonella species can be isolated from cultures of lymph node biopsy specimens. Special culture media are often required.
Treatment of cat-scratch disease in immunocompetent patients is local heat application and analgesics for this typically self-limited disease. If a lymph node is fluctuant, needle aspiration usually relieves the pain.
Antibiotic treatment is not clearly beneficial and generally should not be given for localized infection in immunocompetent patients. However, azithromycin or doxycycline is often given to reduce adenopathy and perhaps decrease the risk of systemic spread. A fluoroquinolone, rifampin, gentamicin, or doxycycline may be used for bacteremia in AIDS patients. Prolonged therapy (eg, weeks to months) is usually necessary for bacteremia to clear. In vitro antibiotic susceptibilities often do not correlate with clinical results.