West Nile Virus

Snapshot

A 34-year-old man presents to a local urgent care after returning from a trip to Africa. He has endured multiple mosquito bites throughout his 2-week safari trip. He states that, like several members of his tour group, he has had a 3-day history of fever, non-itchy rash, and myalgias. One tour group member, however, developed seizures and confusion. This patient is scared that he may also develop severe symptoms like seizures. On physical exam, he has conjunctival injection and a papular rash on his trunk and legs. Given his age and current symptoms, his physician reassures him that it is highly unlikely but to watch out for any signs of meningoencephalitis.

Introduction

Classification
- West Nile virus
  - an enveloped positive single-stranded RNA flavivirus
- transmission
  - Culex mosquitoes
Epidemiology
- demographics
  - more severe in the elderly
  - more common in the young
- risk factors
  - mosquito bites
Pathogenesis
- mosquito’s saliva transmits the virus to human blood
- virus then replicates in dendritic cells and spreads via lymphatics and bloodstream
- in some patients, the virus can invade the central nervous system and cause meningoencephalitis
  - paralysis occurs when neurons are damaged in the anterior horn of the spinal cord
Associated conditions
- West Nile fever
- meningoencephalitis
Prognosis
- most infections are asymptomatic
when symptomatic, the disease may progress to meningitis or encephalitis in < 1% of those infected

Presentation

Imaging

Magnetic resonance imaging (MRI)
- indication
  - meningoencephalitis
- findings
increased signal intensity in affected areas

Studies

Differential

Treatment

Complications