venous occlusive diseases, have been described in association with focal retinitis [113, 118–122].

Other posterior segment ocular complications include epiretinal membrane formation, an inflammatory mass of the optic nerve head, peripapillary angiomatosis, intermediate uveitis, retinal white dot syndromes, orbital abscesses, isolated disc swelling, and panuveitis [113, 118–122].

Genetics

There does not appear to be any genetic influence that alters human susceptibility to ocular bartonellosis.

Diagnosis/Treatment/Complications

The diagnosis of ocular bartonellosis is based on the characteristic clinical findings together with confirmatory serologic testing. The detection of serum anti- Bartonella henselae antibodies is available by indirect fluorescent antibody (IFA) assay. Titers >1:64 are 88% sensitive and 94% specific [123]. Enzyme immunoassays (EIA) together with Western blot analysis have been developed, and are more sensitive than indirect fluorescent antibody tests. A single positive IFA or EIA titer for IgG or IgM antibodies is sufficient to confirm the diagnosis of CSD. Bacterial cultures from primary inoculation sites, lymph nodes, or blood, can be used, but require several weeks for colonies to become apparent. Another diagnostic approach is a skin test for reaction to an intradermal cat-scratch antigen. Fortyeight hours post-inoculation, an area of induraction >5 mm is 79–100% sensitive and 90–98% specific [124]. Lastly, there are PCR based-techniques that target the bacterial 16S rRNA gene or B. henselae DNA, but this test is not readily available [125].

In most cases, CSD is a self-limited illness with an excellent overall systemic and visual prognosis. Because of this, there is no generally accepted first-line medication whose efficacy has been conclusively demonstrated. A variety of antibiotics, including doxycycline, erythromycin, rifampin, trimethoprim/sulfamethoxazole, ciprofloxacin, and gentamycin have been used in severe systemic or ocular disease. Children with CSD may be treated with azithromycin. The efficacy of oral corticosteroids on the course of systemic and ocular disease is not known [108, 110].

19.5.4  Diffuse Unilateral Subacute

Neuroretinitis

19.5.4.1  Historical Context/Pathophysiology

Diffuse unilateral subacute neuroretinitis (DUSN) is an uncommon but important nematode infection that primarily affects the outer retina and retinal pigment epithelium in otherwise healthy, young patients. A motile, subretinal worm was first described and photographed in a living eye by Parsons in 1952. Subsequently, a thorough description of DUSN was formulated by Gass in 1978, but it was known at the time that the clinical syndrome might be due to nematode infestation [126]. Current evidence suggests that DUSN is primarily caused by nematodes of two different sizes that migrate through subretinal space. The smaller worm of 400–1,000 mm in length is more common in the southeastern US and Caribbean, and is believed to be Ancylostoma canium (dog roundworm) or Toxocara canis. The larger worm of 1,500–2,000 mm in length is more common in the northern midwestern US and Canada, and is believed to be Baylisascaris procyonis (raccoon roundworm) [127]. Since these types of nematodes are extremely common, increased recognition may ultimately lead to more cases being diagnosed in other parts of the world.

As nematodes causing DUSN are probably intestinal roundworms, there is likely a fecal-oral route of contamination. Embryonated eggs are ingested from contaminated soil, penetrate intestinal wall as motile larvae, and migrate to the subretinal space. Since virtually none of the cases described have had evidence of systemic larval infection, ocular disease is probably caused by a rare, random event. The relative immune privilege of the eye may permit larvae to survive intraocularly. The exact pathophysiology of DUSN is uncertain, but local gray-white lesions may be inflammatory changes related to toxic effects or immunologic stimulation from excretory products of the larva.

19.5.4.2  Clinical Findings/Natural History

The mean age of patients with DUSN is 14 years, and the disorder is almost always unilateral. The onset of disease is frequently insidious and goes unnoticed, but patients may complain of paracentral or central