Disease
Bartonella henselae is the cause of cat-scratch disease (CSD) and bacillary angiomatosis (BA). CSD is one of the most common zoonotic diseases in the United States.
Important Properties
B. henselae is a small, pleomorphic gram-negative rod. It is a fastidious organism and will not grow on routine blood agar. It can be cultured on specialized media in the clinical laboratory.
Pathogenesis & Epidemiology
Cat scratches or bites, especially from kittens, are the main mode of transmission of B. henselae to humans. The organism is a member of the oral flora of many cats. There is evidence that it is transmitted from cats to humans by the bite of cat fleas. Exposure to cat urine or feces does not pose a risk of transmission. Person-to-person transmission of B. henselae does not play a significant role in infection. B. henselae is a low-virulence organism, and disease is self-limited in immunocompetent individuals.
The pathogenesis of angiomas that occur in Bartonella infections in immunocompromised individuals is uncertain. One current explanation is that infection of endothelial cells by Bartonella induces the synthesis of angiogenesis factor that causes endothelial cells to proliferate.
Clinical Findings
In immunocompetent people, B. henselae causes CSD. This disease is characterized by fever and tender, enlarged lymph nodes, typically on the same side as the scratch (Figure 1). A papule at the site of the scratch may precede the lymphadenopathy. CSD has a prolonged course but eventually resolves, even without antibiotics. A small percentage of those infected develop systemic disease, such as endocarditis or encephalitis.
Fig1. Cat-scratch disease. Note the two enlarged, inflamed axillary lymph nodes in a patient with cat-scratch disease. (Reproduced with permission from Wolff K, Johnson R: Fitzpatrick’s Color Atlas & Synopsis of Clinical Dermatology, 6th ed. New York, NY: McGraw Hill; 2009.)
In immunocompromised individuals, especially patients with acquired immunodeficiency syndrome (AIDS), B. henselae causes BA. BA is characterized by raised, cherry-red vascular lesions in the skin and visceral organs (Figure 2). The lesions appear papular or nodular. Bacillary peliosis (peliosis hepatis) is similar to BA except that in peliosis, the lesions occur primarily in the liver and spleen.
Fig2. Bacillary angiomatosis. Note the cherry-red hemangioma-like skin lesion. (Reproduced with permission from Wolff K, Johnson R: Fitzpatrick’s Color Atlas & Synopsis of Clinical Dermatology, 6th ed. New York, NY: McGraw Hill; 2009.)
Laboratory Diagnosis
The diagnosis of CSD is usually made serologically. Antibodies against B. henselae antigens can be detected in a patient’s serum by a variety of immunologic tests. The organism can be cultured on artificial media but takes 5 days or longer to grow and so is not usually done. The diagnosis of BA is often made by finding pleomorphic rods in biopsy tissue using the Warthin-Starry silver stain. Pathologic examination of tissue from the lesion will distinguish BA from Kaposi’s sarcoma. A PCR test for B. henselae is available.
Treatment & Prevention
No antibiotic therapy is typically recommended for CSD. If the patient has severe lymphadenitis, azithromycin is the drug of choice. Treatment of BA with doxycycline or erythromycin is effective. There is no significant antibiotic resistance. Antibiotics are not recommended for people who have sustained a cat scratch. There is no vaccine.
