Diagnosis: Cat-Scratch Disease
• Bartonella henselae is a gram-negative bacillus that causes intraerythrocytic bacteremia in cats (the reservoir host) and is the most common Bartonella infection of humans worldwide. The spectrum of disease includes cat scratch disease, endocarditis, bacillary angiomatosis, and neuroretinitis. It is transmitted to humans by cat scratch or bite and, possibly, by cat flea bites.
• Classic cat scratch disease begins with an erythematous papule at the infected site and is characterized by fever and cervical or axillary lymphadenopathy that may suppurate.
• Uncomplicated cat scratch disease usually resolves in 1 month and is often treated with tetracyclines, macrolides, or aminoglycosides. Cat scratch disease may progress to infective endocarditis in patients who have a history of previous heart valve injury.
• Isolation of B. henselae is difficult because it is highly fastidious and often does not grow despite 2 to 6 weeks of culture. Diagnosis of infection is best confirmed by the serologic detection of antibodies in the patient’s serum or by molecular detection of B. henselae DNA from the patient’s tissues.
• A Warthin-Starry stain of infected tissue may demonstrate Bartonella henselae in chains, clumps, or filaments within areas of necrosis. Gram stains are usually negative.
