Epidemic West Nile virus encephalitis in Tunisia.

West Nile fever (WNF) is a mosquito-borne flavivirus infection. It is epidemic in Africa and Asia. In autumn 1997, a WNF epidemic occurred in the Sfax area (southeastern Tunisia). Fifty-seven patients were hospitalized with aseptic meningitis and/or encephalitis. Search for specific anti-West Nile virus (WNV) antibodies in serum and cerebrospinal fluid (CSF) was performed using an ELISA test. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to detect the WNV genome in CSF and brain specimens. Recent central nervous system (CNS) infection by WNV was confirmed in 30 patients, probable infection in 17 and it was excluded in 10. In the confirmed subgroup, patients with encephalitis were older than those with meningitis. CSF showed pleocytosis, high protein (47%) and normal glucose levels. Brain computed tomography-scan (CT-scan) and magnetic resonance imaging (MRI) were normal. RT-PCR disclosed WNV genome in the CSF in two cases and in a brain specimen in one. Three patients died rapidly, the remaining cases had favorable prognosis. Autopsy was performed in two cases and showed nonspecific lesions of encephalitis. No viral inclusions were seen with light microscopy. Seropositivity rate in patients' proxies for WNV was 23.4%. Prognosis of CNS involvement during WNF seemed to be poor in older patients. This is the first WNV encephalitis epidemic report in the Sfax area of Tunisia.