A 30-year-old man develops a pustular lesion at the site of a cat scratch on his forearm. This is followed 1 week later by malaise, fever, and lymphadenopathy. On examination, he has tender axillary lymph nodes. Which of the following is the most likely causative organism?
Bartonella henselae
Bartonella bacilliformis
Bartonella quintana
Coxiella burnetii
The cause of cat-scratch fever is a tiny Gram-negative bacillus, B. henselae. Cats acquire the organism from the soil and inoculate humans via scratches or bites. The disease is generally benign and self-limited, and is treated with analgesics and antipyretics. Encephalitis, seizures, coma, meningitis, and transverse myelitis can occasionally occur even in immunocompetent patients. A variety of antibiotics have been used when severe disease is present but an optimal regimen has not been identified.
Infection