cat scratch disease

Cat scratch disease (CSD) is caused by Bartonella henselae, a gram-negative, fastidious, intracellular bacillus. Cats (especially kittens) serve as the reservoir, and transmission occurs via scratch, bite, or contact with cat saliva on broken skin/mucosa. The organism is also transmitted between cats by fleas (Ctenocephalides felis). Pathophysiology: after inoculation, a papule or pustule develops at the scratch site within days, followed 1-3 weeks later by tender regional lymphadenopathy (most commonly axillary, epitrochlear, or cervical) that can persist for weeks to months. Lymph nodes may suppurate. Systemic symptoms are usually mild and include low-grade fever, malaise, headache, and anorexia. Diagnosis is primarily clinical, supported by serology (indirect fluorescent antibody or EIA for Bartonella henselae IgG), PCR of lymph node aspirate, or biopsy showing necrotizing granulomas with stellate microabscesses (though nonspecific, seen in other granulomatous diseases like LGV and tularemia). Warthin-Starry silver stain can demonstrate the organism in tissue. Most cases are self-limited in immunocompetent hosts, resolving over 2-4 months without treatment; however, azithromycin can shorten the duration of lymphadenopathy. Complications include Parinaud oculoglandular syndrome (conjunctivitis with preauricular lymphadenopathy from ocular inoculation), encephalitis, and hepatosplenic granulomas. In immunocompromised patients (e.g., HIV/AIDS with low CD4 counts), Bartonella henselae causes bacillary angiomatosis, a vascular proliferative disease affecting skin and visceral organs, which can mimic Kaposi sarcoma but is treated with antibiotics (erythromycin or doxycycline) rather than being neoplastic. Bartonella quintana, a related species, causes trench fever and is also associated with bacillary angiomatosis, transmitted by body lice. High-yield board associations: cat exposure + tender lymphadenopathy + granulomatous histology = cat scratch disease; HIV patient + skin/visceral vascular lesions = bacillary angiomatosis (Bartonella).