Which organism is the etiologic agent of cat scratch disease?

• A. Bartonella henselae
• B. Borrelia burgdorferi
• C. Staphylococcus aureus
• D. Streptococcus pyogenes

Answer: (A)

Cat scratch disease is caused by Bartonella henselae, a small Gram-negative bacterium that lives inside macrophages and endothelial cells. It’s transmitted when a cat scratch or bite inoculates the bacterium, often involving kittens and flea exposure as part of the transmission cycle. The typical presentation is regional lymphadenopathy near the site of the scratch, sometimes with low-grade fever and malaise. Because the organism is intracellular and fastidious, it’s not always easy to culture with routine methods, so serology or PCR is often used for diagnosis. The other organisms listed are linked to different diseases—Borrelia burgdorferi causes Lyme disease; Staphylococcus aureus and Streptococcus pyogenes are common culprits in skin, soft tissue, and throat infections—so Bartonella henselae best explains cat scratch disease.