I. Basic information

  1. A flavivirus
  2. Related to Japanese encephalitis and St. Louis encephailitis
  3. Can affect humans, horses, birds, and other vertebrates
  4. Transmitted to humans through mosquito bites (various species); no known cases of person-to-person transmission among humans or between humans and non-mosquito species as of 2005, except through blood transfusions, transplacentally, or through breastfeeding

III. Clinical features

  1. Incubation period 3-14d; sx usually last 3-6d
  2. Clinical presentation is indistinguishable from other viral encephalitides
  3. Most cases are mild or asympomatic
  4. "West Nile Fever"--About 20% of cases; sx include fever, malaise, anorexia, n/v, eye pain, HA, myalgias, rash, and lymphadenopathy
  5. Neurologic involvement seen in about .7% of cases:
    1. Encephalitis
    2. Meningitis
    3. Acute flaccid paralysis