Early Interferon-beta Treatment for West Nile Virus

Diagnosis of WNV infection will be based on the following: 1. Patients with clinical presentation suspected as compatible with WNV infection, with symptoms including elevated fever, headache or flaccid paralysis or fever with encephalopathy. And: 2. Positive anti-WNV IgM serology / WNV PCR from either serum, urine or CSF. Inclusion criteria: We aim to focus on three patients' populations: 1. Patients older than 70 years of age, who are at higher risk for the presence of neutralizing anti-Type I IFN auto-antibodies, and therefore at higher risk for developing severe neuroinvasive disease. Only patients who fulfill the diagnostic criteria above will be included. 2. Patients presenting with neuroinvasive WNV disease, including either flaccid paralysis or encephalitis, independent of their age, excluding a presentation consistent with isolated aseptic meningitis (headache, fever, 6th nerve palsy). Only patients who fulfill the diagnostic criteria above will be included. 3. Immunocompromised patients at any age. Immunocompromised patients will be defined as patients with hematologic malignancy (treated or untreated); chemotherapy within previous 4 weeks, stem cell transplant recipient or solid organ transplant recipient; use of any immunosuppressant drug including prednisone greater than or equal to 20 mg/day within the previous 4 weeks; primary / acquired immunodeficiency disorder. Only patients who fulfill the diagnostic criteria above will be included. Exclusion Criteria: 1. Patients younger than 18 years old. 2. Pregnant women. 3. Contraindication for the administration of the drug: Hypersensitivity to natural or recombinant interferon beta, and decompensated liver disease. 4. A patient with neuroinvasive disease showing consistent spontaneous improvement over a period of \> 2 days and mRS of below 4. 5. More than 8 days from onset of neurological symptoms in immunocompetent patients and more than 10 days in immunocompromised patients. This time frame will be renewed if a patient with flaccid paralysis develops new onset encephalitis. 6. Patients who are receiving active chemotherapy treatment or suffer concurrent severe viral infection.