West Nile virus (flavivirus infection)

• What is West Nile Virus (viral encephalitis, western equine encephalitis)
• Statistics on West Nile Virus (viral encephalitis, western equine encephalitis)
• Risk Factors for West Nile Virus (viral encephalitis, western equine encephalitis)
• Progression of West Nile Virus (viral encephalitis, western equine encephalitis)
• Symptoms of West Nile Virus (viral encephalitis, western equine encephalitis)
• Clinical Examination of West Nile Virus (viral encephalitis, western equine encephalitis)
• How is West Nile Virus (viral encephalitis, western equine encephalitis) Diagnosed?
• Prognosis of West Nile Virus (viral encephalitis, western equine encephalitis)
• How is West Nile Virus (viral encephalitis, western equine encephalitis) Treated?
• West Nile Virus (viral encephalitis, western equine encephalitis) References

What is West Nile Virus (viral encephalitis, western equine encephalitis)

West Nile virus is transmitted by mosquitos and causes an illness that ranges from mild to severe. Mild, flu-like illness is often called West Nile fever. More severe forms of disease, which can be life-threatening, may be called West Nile encephalitis or West Nile meningitis, depending on where it spreads.
WNV virus is endemic in the Middle East, Africa, and Asia. In North America, WNE first occurred in the northeast United States along the eastern seaboard and now extends to Florida, the Gulf Coast, and several western states.

Statistics on West Nile Virus (viral encephalitis, western equine encephalitis)

In the US: Cases initially occurred in the greater New York area, but cases have now occurred in western states. Wild birds with WNE virus have been found in many states and in Canada.
Furthermore, the cluster of recent outbreaks in Romania, Russia, the Congo, and the United States is characterized by a low frequency of classic WNE features but a high rate of encephalitis and death.
Internationally: WNE seropositivity of children in Egypt is approximately 50%. WNE is the most common cause of viral aseptic meningitis or encephalitis in patients presenting to emergency departments in Cairo. WNE is common in the Middle East, Asia, and Africa.

Risk Factors for West Nile Virus (viral encephalitis, western equine encephalitis)

Risk factors for developing a worse form of the disease likely include the following:

• Conditions that suppress the immune system
• recent chemotherapy
• recent organ transplantation
• HIV
• Pregnancy
• Older age

West Nile virus may also be spread through blood transfusions and organ transplantation. It is possible for an infected mother to transmit the virus to her child via breast milk.

Progression of West Nile Virus (viral encephalitis, western equine encephalitis)

Patients with WNE may present with features of encephalitis, aseptic meningitis (meningoencephalitis), or both.

How is West Nile Virus (viral encephalitis, western equine encephalitis) Diagnosed?

 

• FBC — may show a normal or elevated white blood cell (WBC) count
• Lumbar puncture and cerebrospinal fluid (CSF) testing
  • usually shows elevated WBC count (especially lymphocytes)
  • usually shows elevated protein level

   

• Head CT scan — often normal
• Brain MRI scan — may show evidence of inflammation (in about one-third of patients)
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  Prognosis of West Nile Virus (viral encephalitis, western equine encephalitis)

  In general, the likely outcome of a mild West Nile virus infection is excellent.
  For patients with severe cases of West Nile virus infection, the outlook is more guarded. West Nile encephalitis or meningitis has the potential to lead to brain damage and death. Approximately 10% of patients with brain inflammation do not survive.
  

  How is West Nile Virus (viral encephalitis, western equine encephalitis) Treated?

  Because this illness is not caused by bacteria, antibiotics do not help treat West Nile virus infection. Standard hospital care may help decrease the risk of complications in severe illness. There is no human vaccine available at present, and it is likely there will not be one for several years.
  

  West Nile Virus (viral encephalitis, western equine encephalitis) References

  1. Acute Flaccid Paralysis Syndrome Associated with West Nile Virs Infection – Mississippi and Louisiana, July-August, 2002. MMWR 2002; 51: 825-828.
  2. Asnis DS, Conetta R, Teixeira AA, et al: The West Nile Virus outbreak of 1999 in New York: the Flushing Hospital experience. Clin Infect Dis 2000 Mar; 30(3): 413-8.
  3. eMedicine.
  4. Medline Plus.