The patient in the clinical vignette is experiencing cat scratch disease which is transmitted by, as the name implies, a cat scratch or bite.
Cat scratch disease is caused by a small pleomorphic, oxidase negative, aerobic, Gram-negative rod called Bartonella Hensalae; it is carried in the saliva of asymptomatic, bacteremic cats. When the cat scratches or bites a human, a small papule forms within a few days followed by lymphadenopathy in the affected region and generalized fever. If a biopsy is performed on the enlarged lymph nodes, B. hensalae can be visualized using a Warthin-Starry silver stain.
Klotz et al. review cat scratch disease which typically presents as tender lymphadenopathy and fever of unknown origin. Cats serve as the vectors of transmission to humans via a bite or a scratch from the cat and cat fleas serve as the vector of transmission between cats (horizontal transmission). Culturing of B. hensalae is difficult, therefore the diagnosis relies on a history of cat exposure and immunoglobulin G reactivity towards B. hensalae. Most cases resolve spontaneously, but if an antibiotic is given, azithromycin may be administered.
Smith reviews B. hensalae infections such as bacillary peliosis hepatitis and splenitis, bacillary angiomatosis, and cat scratch disease. A large percentage of young cats carry this bacteria but complications resulting from this bacteria are rare in the immunocompetent. If an individual does experience cat scratch disease, antibiotics are not necessary as the individual will recover spontaneously but more severe cases have shown to be responsive to erythromycin and doxycycline.
Image A shows suppurative right axillary lymphadenopathy secondary to cat scratch disease.
Illustration A demonstrates a Warthin-Starry stain of a lymph node containing B. hensalae which stain as black clumps or stains.
Answer 1: Leptospira is transmitted via animal urine.
Answer 3: Parrots are a vector of transmission of Chlamydophila psittaci.
Answer 4: Armadillos are a vector of transmission for Mycobacterium leprae.
Answer 5: Rabbits are a vector of transmission for Francisella tularensis.
Klotz SA, Ianas V, Elliott SP. Cat-scratch Disease. Am Fam Physician. 2011 Jan 15;83(2):152-5. Review.
PMID:21243990 (Link to Abstract)
Smith DL. Cat-scratch disease and related clinical syndromes. Am Fam Physician. 1997 Apr;55(5):1783-9, 1793-4. Review.
PMID:9105205 (Link to Abstract)