Necrotizing granulomatous lymphadenitis caused by Bartonella henselae. A cat scratch, bite, or lick introduces the bacteria at the site of cutaneous inoculation, causing a self-limited infection, the cat scratch disease (CSD).

In the United States, approximately 22,000 cases are diagnosed annually, although many more cases may go unrecognized (1). National databases reveal an estimated incidence of 9.3 cases of CSD per 100,000 population per year; 55% of patients are 18 years of age or younger, and the distribution varies seasonally, with the majority of cases occurring between September and January (2). Patients, particularly children, report contact with a cat in 90% of cases and cat scratch or bite in three-fourths of these (3). The cats—young, healthy, and usually with fleas—are the reservoir for the B. henselae organism and act as the vector for the disease, as first recognized by Robert Debre in 1931 (1,3,4,5,6). In cats, B. henselae resides in erythrocytes and does not cause serious illness (7). In the United States, cats frequently have bacteremia with B. henselae (41% of cats in the San Francisco area) (5).

The bacterial pathogens of CSD, B. henselae, are gram-negative pleomorphic bacilli appearing as small rods 0.3 to 1.0 μm by 0.6 to 3.0 μm, or as coccoid or L-shaped forms singly, in chains, or in clumps (8). They are located in foci of necrosis and vessel walls, and characteristically in the vicinity of collagen fibers (8,9,10). CSD bacteria are faintly stained by the Brown-Hopps Gram’s stain but not by the Brown-Brenn Gram’s stain (8,9). The best results are obtained with formalin-fixed tissues stained with the Warthin-Starry silver impregnation stain, which slightly enlarges the microorganisms by depositing silver, thus increasing their visibility (8). CSD bacilli from the lymph nodes of patients with CSD lymphadenitis have been successfully cultured, and antisera to CSD bacilli have been produced (11). During the past 40 years, a variety of microbial agents have been suspected to be the cause of CDS. In 1988, with the use of the Warthin-Starry silver stain by D. Wear at the Armed Forces Institute of Pathology (AFIP), a bacterial agent was visualized in CSD lymphadenitis, then fully characterized and named Afipia fellis (8,11,12). Over the ensuing decade, bacillary angiomatosis was described in AIDS patients and Rochalimaea henselae identified as its etiologic agent (13). Subsequently, it was noted that patients with CSD have a high rate of seropositivity for R. henselae and a very low rate for A. felis, which caused a change in theories and nomenclatures (14). Based on genetic similarities, when prokaryotic ribosomal gene DNA extracted from organisms of various lesions was compared, it became apparent that the agent of CSD was R. henselae. Specific nucleic acid sequences of R. henselae were found in 84% of CSD lymph nodes studied (13,14,15,16). As a result of the genotypic evaluation, a change in nomenclature was proposed: the old genus Rochalimaea has been replaced by the genus Bartonella, and the agent of CSD has been designated as B. henselae (17,18,19,20). The genus Bartonella now includes B. henselae, B. quintana, and B. bacilliformis. According to current theories, CSD is caused by B. henselae, with flea-borne transmission to kittens that constitute the reservoir of the disease. The same bacterium, singly or in association with B. quintana, may cause bacillary angiomatosis in patients with the severe immune deficiency of AIDS (13,21,22,23).

Cat-scratch bacilli cause a spectrum of diseases, depending on the immunocompetence of the host (8,23). In normal, immunocompetent persons, within 3 to 10 days, the primary lesion that may be present in 20% to 50% of cases appears as an area of erythema at the site of the cat scratch. This is followed by a papular and then a vesicular lesion that oozes fluid and eventually dries to form a scab (24,25). Most often, the upper extremities are affected, followed by the cervical and facial regions. After 1 to 3 weeks, regional lymphadenopathy appears. This is usually unilateral and involves axillary, epitrochlear, cervical, or inguinal lymph nodes. One lymph node is involved in 50% of cases and multiple nodes, usually in the same region, in 30% of cases (1). The lymphadenitis may be associated with fever, malaise, headache, or aches of bones and joints. A distinctive manifestation of CSD is Parinaud oculoglandular syndrome, a moderate conjunctivitis with preauricular lymphadenopathy occurring when the site of inoculation was the conjunctiva or the eyelid. The involved lymph nodes are enlarged, nodular, matted, and adherent to the surrounding soft tissues and skin (Fig. 17.1). The sections show focal areas of necrosis and, on occasion, formation of microabscesses (Figs. 17.2 and 17.3). In the general population, CSD is a benign, self-limited illness, lasting 6 to 12 weeks in the absence of treatment (6). It is characterized by lymphadenitis, which is most common in children (26), with possible suppuration in 10% of cases (1). In contrast, in patients with AIDS, CSD may result in a systemic, severe, and sometimes life-threatening disease with involvement of multiple internal organs (27,28,29).