(Bartonella henselae)

The predominant manifestation of cat-scratch disease (CSD) in an immunocompetent person is regional lymphadenopathy. Fever and mild systemic symptoms occur in approximately 30% of patients. A skin papule or pustule often is found at the presumed site of bacterial inoculation and usually precedes development of lymphadenopathy by 1 to 2 weeks. Lymphadenopathy involves nodes that drain the site of inoculation-typically axillary, but cervical, submental, epitrochlear, or inguinal nodes can be affected. The skin overlying affected lymph nodes typically is tender, warm, erythematous, and indurated. In approximately 25% of people with CSD, the affected nodes suppurate spontaneously. Occasionally, infection can produce Parinaud oculoglandular syndrome, in which inoculation of the eyelid conjunctiva results in conjunctivitis and ipsilateral preauricular lymphadenopathy. Less common manifestations of CSD (approximately 25%) include encephalopathy, aseptic meningitis, fever of unknown origin, neuroretinitis, osteolytic lesions, hepatitis, granulomata in the liver and spleen, glomerulonephritis, pneumonia, thrombocytopenic purpura, erythema nodosum, and endocarditis.

Etiology

Bartonella henselae , the causative organism of CSD, is a fastidious, slow-growing, gram-negative bacillus that also is the causative agent of bacillary angiomatosis (vascular proliferative lesions of skin and subcutaneous tissue) and bacillary peliosis (reticuloendothelial lesions in visceral organs, primarily the liver). The latter 2 manifestations of infection are reported primarily in patients with human immunodeficiency virus infection. B henselae is closely related to Bartonella quintana , the agent of louseborne trench fever and a causative agent of bacillary angiomatosis and bacillary peliosis. B quintana also can cause endocarditis.

Epidemiology

CSD probably is a common infection, although the true incidence is unknown. Cats are the natural reservoir for B henselae , with a seroprevalence of 81% in stray cats and 28% in domestic cats in the United States. Cat-to-cat transmission occurs via the cat flea (Ctenocephalides felis) , with infection resulting in bacteremia that usually is asymptomatic and lasts weeks to months. Kittens are more likely to be bacteremic than are older cats. Most reported cases occur in people younger than 20 years of age, with more than 90% of patients having a history of recent contact with apparently healthy cats, often kittens. No evidence of person-to-person transmission exists. Infection occurs more often during the autumn and winter. The role of fleas or other arthropods in transmission of B henselae to humans is not well established.

The incubation period from the time of the scratch to appearance of the primary cutaneous lesion is 7 to 12 days; the period from the appearance of the primary lesion to the appearance of lymphadenopathy is 5 to 50 days (median, 12 days).

Diagnostic Tests

The indirect immunofluorescent antibody (IFA) assay for detection of serum antibodies to antigens of Bartonella species is useful for diagnosis of CSD. The IFA test is available at many commercial laboratories and through the Centers for Disease Control and Prevention (CDC). Enzyme immunoassays for detection of antibodies to B henselae have been developed; however, they have not been demonstrated to be more sensitive or specific than the IFA test. Polymerase chain reaction assays are available in some commercial and research laboratories and at the CDC. If tissue (eg, lymph node) specimens are available, bacilli occasionally may be visualized using Warthin-Starry silver stain; however, this test is not specific for B henselae . Early histologic changes in lymph node specimens consist of lymphocytic infiltration with epithelioid granuloma formation. Later changes consist of polymorphonuclear leukocyte infiltration with granulomas that become necrotic and resemble granulomas from patients with tularemia, brucellosis, and mycobacterial infections.

Treatment

Management of localized CSD primarily is aimed at relief of symptoms, because the disease usually is self-limited, resolving spontaneously in 2 to 4 months. Painful suppurative nodes can be treated with needle aspiration for relief of symptoms; incision and drainage should be avoided, and surgical excision generally is unnecessary.

Antimicrobial therapy may hasten recovery in acutely or severely ill patients with systemic symptoms, particularly people with hepatic or splenic involvement or painful adenitis, and is recommended for all immunocompromised people. Reports suggest that several oral antimicrobial agents (azithromycin, erythromycin, ciprofloxacin, trimethoprim-sulfamethoxazole, and rifampin) and parenteral gentamicin are effective, but the role of antimicrobial therapy is not clear. The optimal duration of therapy is not known.

Antimicrobial therapy for patients with bacillary angiomatosis and bacillary peliosis has been shown to be beneficial and is recommended. Azithromycin, erythromycin, and doxycycline are effective for Treatment of these conditions; therapy should be administered for several months to prevent relapse in immunocompromised people.

Isolation of the Hospitalized Patient

Standard precautions are recommended.

Control Measures

People, especially children, should avoid playing roughly with cats and kittens to minimize scratches and bites. Stray cats should not be handled by children. Immunocompromised people should avoid contact with cats that scratch or bite and, when acquiring a new cat, should avoid cats younger than 1 year of age or stray cats. Sites of cat scratches or bites should be washed immediately. Care of cats should include flea control. Testing of cats for Bartonella infection is not recommended.