West Nile virus (WNV) is an important emerging flavivirus resulting in acute and sometimes fatal encephalitis in humans. In animal models, WNV can persistently infect the central nervous system (CNS) and the kidneys. We became concerned that a similar persistent infection could occur in humans when we discovered a larger than expected number of WNV patients in our cohort were experiencing progressive neurologic disease and kidney failure. The applicant has a large, well-documented cohort of 112 WNV patients who she has followed since 2002. We have found that 77% of patients who presented with encephalitis have abnormal neurologic exams, including 63% who have impaired tandem gait, suggestive of vestibular-cerebellar and/or dorsal column dysfunction. Additionally, 23% of patients developed renal disease, including 5 who died from renal failure. Our preliminary research found associations between persistence of symptoms, sustained detectable IgM antibody response, and altered cytokine expressions, which strengthened our hypothesis that some patients might have persistent infection. Recently, we reported 5 out of 25 (20%) cohort participants' urine contained WNV viral RNA, which is the first ever documented evidence of persistent WNV infection in humans. Two of these individuals are in renal failure. Further testing of the cohort has revealed a total of 21/55 (38%) patients shedding WNV RNA in the urine; 45% of these patients reported developing kidney disease after their acute infection. Our findings are very novel and worrisome considering more than 25,000 WNV patients across the US have been reported to CDC. We urgently need to further investigate the pathologic lesions underlying these gross endpoints and the clinical parameters that define persistent infection with WNV, which is the goal of this proposal. Thus, the objective of the proposed study is to determine the renal and neurological pathology and outcomes associated with persistent infection with WNV. We plan to identify the degree of renal failure and pattern of shedding of virus in the urine, identify the infected cell types through histopathologic examination of renal biopsies, genotypic and phenotypic analysis of virus isolates to determine mutations potentially related to renal tropism, and perform neurocognitive examinations, volumetric MRI, and electrophysiological studies to determine the location of pathologic lesions in the CNS. It is the hypothesis of this proposal that persistent infection is associated with severe and progressive renal and neurological pathology. This research will provide the information necessary to evaluate patients for persistent infection and develop treatment protocols.