Saint Louis encephalitis virus

Background

• Single-stranded positive-sense enveloped virus in the family Flaviviridae and genus Flavivirus
• Reservoir is birds
• Vector-borne, transmitted by Culex mosquitoes
• Outbreaks have occurred in the US, Canada, and Mexico, with sporadic cases in Central and South America

Clinical Manifestations

• Incubation period 4 to 21 days
• Risk of encephalitis is highest in older age >60 years
• Presents with non-specific febrile illness with severe headache and meningismus, followed by focal neurological deficits including brainstem, cerebellum, and cranial nerves
• Tremors of the eyelids, tongue, lips, and extremities
• Seizures are uncommon
• Usually no motor or sensory deficits, but may develop urinary symptoms

Prognosis and Complications

• Mortality 5-15%, but higher in the elderly
• Up to half of survivors have neuropsychiatric symptoms persisting at 3 years

Diagnosis

• Serology demonstrating IgM in CSF or serum

Management

• Supportive