DIFFUSE UNILATERAL SUBACUTE NEURORETINITIS - MORPHOMETRIC, SEROLOGIC,AND EPIDEMIOLOGIC SUPPORT FOR BAYLISASCARIS AS A CAUSATIVE AGENT

Purpose: Several nematodes have been postulated as etiologic agents in diffuse unilateral subacute neuroretinitis (DUSN), but the cause of t his condition remains uncertain. The authors report the first case of DUSN from the western United States (northern California), along with morphometric, serologic, and epidemiologic evidence supporting Baylisa scaris procyonis as its cause. Methods: One patient was examined and e valuated for disc edema and transient obscurations of vision. A diagno sis of DUSN was confirmed when a motile nematode was identified within the substance of the patient's retina. Morphometric analysis of the n ematode was done from projected fundus photographs. Serologic evidence of Baylisascaris infection was suggested by Western blot analysis. A necropsy was done on 12 raccoons from the area. They were examined for evidence of Baylisascaris infection, previously believed to be nonend emic in the region. Results: The intraocular nematode measured 1727 X 67 mum, most consistent with Baylisascaris. The patient had considerab le exposure to raccoons, and was seropositive for B. procyonis infecti on on Western blot analysis. Necropsy evaluation showed B. procyonis i nfection in 8 of 12 raccoons examined from the area.Conclusions: The m orphometric, serologic, and epidemiologic findings in this case provid e evidence that the raccoon ascarid, B. procyonis, is a cause of the l arge nematode variant of DUSN.