What is the prognosis of West Nile virus (WNV) infection and encephalitis (WNE)?

Updated: Apr 05, 2021
  • Author: David J Cennimo, MD, FAAP, FACP, AAHIVS; Chief Editor: Michael Stuart Bronze, MD  more...
  • Print

West Nile fever generally has an excellent prognosis. Most WNV infections (70%-80%) are asymptomatic and self-limited. Cases that prove to be symptomatic may produce symptoms that range from a mild febrile illness to a severe lethal encephalitis. [3]  94% of patients with encephalitis or other neuroinvasive disease were hospitalized with the highest hospitalization rates in those  ≥70 years (98%). In an analysis of data from 2009-2018, CDC reported 1,154 (9%) of neuroinvasive disease cases resulting in death. The case-fatality ratio increased with increasing age; 2% of cases among patients aged < 50 years were fatal, compared with 6% of cases among those aged 50–69 years and 21% of those aged ≥70 years. [3]  These findings were similar to the range of 7%-10% as reported in prior years. [8]  Other age-adjusted risk factors positively correlated with death due to WNE include chronic kidney disease, hepatitis C virus infection, and immunosuppression. [10]  Significant risk factors associated with development of WNE (as opposed to West Nile fever), as well as increased mortality risk, includes advanced age, malignancy, or organ transplant recipient status. [11]  Other important risk factors for development of WNE include hypertension, cardiac disease, diabetes, alcohol abuse, and male sex. [10, 12]

Patients who recover from WNE may be left with considerable long-term morbidity and functional deficits. [13]  About two-thirds of patients who develop paralysis during the disease course retain significant weakness in that extremity. [13]  Besides muscle weakness, other, more complex, neurocognitive deficits may develop, including memory loss. [14]  A small case series showed that symptoms such as fatigue, headache, and myalgias tended to persist at 8 months postinfection, with roughly 40% maintaining their gait or movement symptoms. [15]  Those with WNE who developed meningitis or encephalitis had better neurological recovery at 8 months than those with acute flaccid paralysis. [15]


Did this answer your question?
Additional feedback? (Optional)
Thank you for your feedback!