West Nile virus belongs to the flavivirus genus of the flaviviridae family, the same genus as Japanese encephalitis, St. Louis encephalitis, yellow fever, dengue fever, and hepatitis C. There is a capsule membrane, single-stranded linear ribonucleic acid, RNA is a positive strand, about 10,000 to 11,000 base pairs, and it is infectious. When a patient is infected with West Nile virus and presents with clinical manifestations, IgM can be found in almost all collected cerebrospinal fluid (CSF) and serum samples. Serum IgM antibodies may persist for more than a year.