Cat Scratch Disease (Bartonellosis)

GENERAL PRINCIPLES

B. henselae is facultative intracellular, coccobacillus that can be transmitted from animals to humans

through a bite or scratch. Other Bartonella spp. are transmitted by vectors (e.g., fleas, lice) and include B.

Clinical Presentation

• Cat scratch disease is usually a self-limiting disease with few papulopustular lesions appearing 3-30 days after a cat bite or scratch, followed by regional lymphadenitis (usually cervical or axillary) and mild constitutional symptoms. Atypical presentations include oculoglandular disease (Parinaud syndrome), encephalopathy, retinitis (stellate exudates), arthritis, FUO, and culture-negative endocarditis.

• In immunocompromised hosts, especially HIV-infected patients with a CD4 count of infected livestock (e.g., cattle, sheep, and goats). Urban outbreaks have also been reported from cats and rabbits.

C. burnetti undergoes antigenic variation which forms the basis of differentiating acute from chronic Q fever. When C. burnetti express phase I antigen, it is highly infectious and a single bacteria is sufficient to cause disease.

DIAGNOSIS

Clinical Presentation

• Q fever commonly presents acutely as a mild, self-limiting, subacute fever; but it is also a well-known cause of FUO.

• Atypical pneumonia with fever and headache is the predominant presenting symptom. Chest radiography demonstrating a coin-shaped pulmonary infiltrate (round pneumoniae) is a classic finding.

• Endocarditis is the well-characterized chronic form of Q fever, presenting with subacute constitutional symptoms. In the right epidemiological setting, the presence of a heart valve vegetation with negative blood cultures should always prompt diagnostic testing for Q fever.

Diagnostic Testing

Diagnosis is based on detection of phase I and II, IgM and IgG antibodies, as C. burnetti does not grow in standard routine cultures. Acute infection is characterized by a fourfold rise of phase II antibodies between serum samples taken 3-6 weeks apart. Phase I antibodies become dominant as the infection becomes chronic and a single phase I IgG titer >1:800 is diagnostic in chronic Q fever.⁵⁶ In tissue histopathology, Q fever is a cause of granulomatous inflammation, typically ring shaped (“donut granuloma”).

TREATMENT

• Acute Q fever pneumonia and hepatitis are treated with doxycycline 100 mg PO q12h for 14 days. Macrolides, fluoroquinolones, and TMP-SMX are alternative drugs.

• Chronic Q fever, including endocarditis, is treated with doxycycline 100 mg PO q12h and hydroxychloroquine 200 mg PO q8h for 18-24 months. Repeat serological testing every 3 months to document response is recommended. Cure is established when phase I IgG titers fall below 1:800.