Viral etiology of adult encephalitis in Egypt: the role of West Nile Virus

West Nile Virus (WNV) is a neurotropic virus in the Orthoflavivirus genus of the Flaviviridae family that typically causes asymptomatic infections. Despite the high seroprevalence of WNV in Egypt, no documented cases of neurological involvement were previously recorded. This study aimed to document the causes of encephalitis, including WNV, in Egypt. Data were extracted retrospectively from laboratory records of adult patients suspected of encephalitis who underwent cerebrospinal fluid (CSF) and serum examinations during the study period (2018–2024). Eligible records were identified using the laboratory information system. Non-viral causes were detected in (4%) of the patients. Approximately 7% of patients tested positive for WNV IgM in serum and/or CSF, and one patient tested positive for WNV RT-PCR in CSF. Herpes simplex virus (HSV) (4%) and BK virus (4%) were also identified using real-time PCR. West Nile virus should be recognized as a potential cause of encephalitis in Egypt. Routine testing for WNV in encephalitis investigations is recommended to improve the detection of arboviral neuroinvasive diseases and support effective public health monitoring.