Diffuse unilateral subacute neuroretinitis (DUSN) is a progressive parasitic disease affecting the outer retina and retinal pigment epithelium (RPE). This syndrome is primarily unilateral, although bilateral cases have occurred.  DUSN has been reported to develop in association with other infectious processes such as catscratch disease caused by Bartonella henselae  and herpes simplex virus type 2 infection  . The ocular findings of DUSN include visual loss, vitreous cells, optic disc inflammation and leakage, and transient recurrent crops of gray-white outer retinal lesions. [4, 5, 6]
Stationary or migrating nematodes have been identified deep in the retina or in the subretinal space. Later in the course of the disease, slowly progressive RPE changes and optic atrophy may be observed, as well as narrowing of the retinal vessels.
The exact pathophysiology is uncertain, but the local inflammatory changes may be related to toxic effects or immunologic stimulation from excretory products of the larva or from release of unknown soluble tissue toxins. The fleeting gray-white lesions in the outer retina appear to be a local reaction to noxious stimulation. The loss of vision and progressive optic atrophy secondary to death of ganglion cells and neural fibers may be a remote reaction to soluble toxins.
The southeast and the upper Midwest are known endemic areas for the disease.
DUSN has been reported initially in the Caribbean islands, Brazil, Ghana, and Germany. [7, 8] In the last few years, DUSN has been reported in many other countries, including China,  India,  South Africa, Spain, and Korea  .
No cases of mortality have been reported. Four cases of severe neurologic degeneration with DUSN have been reported in children.
The natural history of untreated DUSN involves multiple recurrent episodes of diffuse and focal inflammation of the retina and RPE with secondary progressive visual loss and optic atrophy in the affected eye.
It rarely affects the fellow eye. Only 2 cases with bilateral involvement have been reported.
DUSN does not show any particular racial preference.
This condition occurs more frequently in males than in females.
It occurs most frequently in the second and third decades. Young children and older adults also may be affected.
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