Most persons infected with WNV are asymptomatic; only 20-30% of infections become symptomatic. When symptoms do occur, their onset is typically 3 to 14 days after infection. West Nile fever (WNF) is the most common clinical syndrome, which is characterized by an acute systemic febrile illness (see table below). Gastrointestinal symptoms and a transient maculopapular rash also are common.
Less than 1% of infected persons develop neuro-invasive disease, which typically manifests as meningitis, encephalitis, or acute flaccid paralysis. Rarely, cardiac dysrhythmias, myocarditis, rhabdomyolysis, optic neuritis, uveitis, chorioretinitis, orchitis, pancreatitis, and hepatitis have been described in patients with WNV disease. More information is available on the Centers for Disease Control and Prevention (CDC) WNV Clinical Evaluation and Disease website.