West Nile Virus Surveillance Program

Health Care Professionals

Background Information

  • First isolated in 1937 in Uganda from blood of a febrile woman.
  • Family: Flaviviridae
    • Genus: Flavivirus
    • Japanese Encephalitis Antigenic Complex
    • Complex includes: Alfuy, Japanese encephalitis, Kokobera, Koutango, Kunjin, Murray Valley encephalitis, St. Louis encephalitis, Stratford, Usutu, and West Nile viruses.
  • All are transmissible by mosquitoes, many can cause febrile, sometimes fatal, illnesses in humans.

West Nile Fever: Human Disease

  • Asymptomatic to mild illness
  • Incubation period 5-15 days
  • Fever, influenza-like illness with abrupt onset
  • Moderate to high fever
  • Headache, sore throat, backache, myalgia, arthralgia, fatigue, vomiting, conjunctivitis
  • Rash, lymphadenopathy
  • Acute aseptic meningitis or encephalitis
  • Most fatal cases >50 years old.

Health Risks for Humans

  • Birds are more likely to be infected than humans.
  • Birds are more likely than humans to be ill.
  • Most mosquitoes are not infected with WN.
  • In northern areas the highest risk of virus transmission in humans is in Aug and Sept.
  • Most people infected do not become ill.
  • Older and immuno-compromised are at greater risk of becoming seriously ill.
  • Children are not in a higher risk group.

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