The estimated annual occurrence of CSD in the United States is 9.3 per 100,000 people, with the highest agespecific incidence among children less than 10 years old [113, 114]. Eighty percent of patients are younger than 21 years of age [114]. In the United States, CSD is most common in the southern states, California, and Hawaii. In temperate climates, the disease follows a seasonal pattern, with the highest number of cases in the fall and winter.

Cats are the primary mammalian reservoir of B. henselae, and the cat flea is thought to be an important vector for transmission of organism among cats [115]. The disease is transmitted to humans by scratches, licks, and bites of domestic cats, particularly kittens [116]. Human to human transmission has not been reported, and no data support transmission from fleas to humans.

In immunocompetent patients, Bartonella infection causes a granulomatous and suppurative response. In immunocompromised patients, the response can be a vasculoproliferative disease called bacillary angiomatosis, which mostly involves the skin but can become disseminated. Histopathological specimens of conjunctival tissue and lymph nodes demonstrate granulomatous necrosis, a mixed cellular infiltrate, and a reactive follicular hyperplasia. Typically, there is a central acellular necrotic area surrounded by lymphocytes, epithelioid cells and histiocytes. Numerous bacillary organisms may be present in vessels walls and are more likely found in the presence of necrosis and granuloma formation [109].

19.5.3.2  Clinical Findings/Natural History

In more than 90% of cases of CSD, an initial inoculation is followed by an incubation period of 3–12 days and the subsequent development of one or more cutaneous erythematous papules or pustules at the inoculation site [117]. Over 1–3 weeks the primary lesion recedes as regional lymphadenopathy appears; it is often the symptom that prompts medical evaluation. Systemic manifestations include a mild to moderate flu-like illness. Ocular involvement, present in 5–10% of patients with CSD, appears approximately 2–3 weeks later. Less commonly, more severe and disseminated disease may develop that is associated with encephalopathy, aseptic meningitis, osteomyelitis, hepatosplenic disease, pneumonia, pleural and pericardial effusions.

Fig. 19.9  The photograph reveals neuroretinitis in a patient with cat scratch disease

The most common ocular involvement, present in 5% of patients with CSD, is a unilateral granulomatous conjunctivitis and regional preauricular and submandibular lymphadenopathy termed Parinaud oculoglandular syndrome. There is a wide array of posterior segment findings in CSD, the most wellknown of which is a neuroretinitis present in 1–2% of patients (Fig. 19.9). It consists of a constellation of findings that includes abrupt visual loss, unilateral optic disc swelling, and macular star formation. Initial presenting vision varies between 20/25 to worse than 20/200. It is now known that this syndrome, formerly known as idiopathic stellate maculopathy and later renamed Leber idiopathic stellate neuroretinitis, is caused by B. henselae infection in approximately two thirds of cases. Most patients with Bartonella-associated neuroretinitis exhibit some degree of anterior chamber inflammation and vitritis. Two to four weeks prior to the appearance of the macular star, optic disc edema associated with peripapillary serous retinal detachment has been observed, and may be a sign of systemic B. henselae infection. Development of the macular star is variable and may be partial, in which case it is usually nasal to the macula. In typical cases the macular star resolves in approximately 8–12 weeks [113, 118–121].

Another common posterior segment finding is discrete, focal, or multifocal retinal and/or choroidal lesions that may occur in the presence or absence of disc edema or exudates. These focal white lesions, measuring 50–300 mm in size, can involve the inner retina and overlie vessels, and may look like cotton-wool spots. When present, these lesions strongly support for diagnosis of B. henselae infection. Localized neurosensory macular detachments, as well as both arterial and