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Category: Infections | Neurology

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West Nile Virus overview

Published: July 17, 2009. Updated: August 09, 2009

West Nile virus belongs to a family of viruses called flavivirus. Although most people infected with the virus more often get a fever that resolves gradually, it can occasionally cause aseptic meningitis (inflammation of the tissues covering the brain and spinal cord) and severe encephalitis (inflammation of the brain); these serious infections are particularly common among children and the elderly.

The main reason for concern is that this virus is carried and transmitted among wild birds and animals (including humans) by Culex mosquitoes. Meaning, that spread of this dangerous virus can be very rapid in areas where the Culex mosquitoes are common.

The virus was more commonly found in Africa, the Middle East, southern Europe, and Asia. In 1996 West Nile virus caused more than 300 cases of CNS disease, with 10% mortality, in the Danube flood plain, including Bucharest. In 1999 the virus appeared in New York City, causing more than 60 cases of aseptic meningitis or encephalitis among humans as well as among crows, exotic zoo birds, and other avians. Since then it has spread rapidly to more than 40 states, infecting birds, humans and horses. >In addition, the virus has been implicated in severe and fatal hepatic necrosis in some parts of Africa. In 2002, the Centers for Disease Control and Prevention (CDC) reported more than 4,000 human infections in the United States. The disease threatens to spread farther in the Americas via bird migration.

What are the symptoms?>

The Incubation Period of West Nile Virus is 3-6 days.

Common signs and symptoms of West Nile virus infection include:

  • Fever
  • Headache
  • Muscle aches
  • Backache
  • A maculopapular skin rash
  • Lymph gland enlargement

If the infection involves the brain (not common) the signs and symptoms may also include:

  • Severe headache
  • Stiff neck
  • Tremors and convulsions
  • Muscle weakness
  • Delirium
  • Coma

Infection is seasonal and starts in spring with a peak incidence in August (when mosquitoes are more common).

The encephalitis was most severe among the elderly and was often associated with notable muscle weakness and even with flaccid paralysis.

When should a patient seek medical attention

When the signs and symptoms above appear in spring or summer and especially if you live in an area that is known to have reported cases of West Nile virus infection, you should seek medical attention.


This should be confirmed by serum detection of antibodies (IgM) in the serum of patients. PCR technique for the detection of viral DNA. Viral blood cultures should be performed. A lumbar puncture and CSF (cerebrospinal fluid) analysis of lymphocytic counts can help exclude septic meningitis due to bacterial (not viral) infection.


No specific viral therapy is available. Patients may need to be hospitalized if they develop CNS disease. Treatment is usually limited to supportive care. Some patients may require more aggressive supportive care in the intensive care unit.


  • People should stay away from any dead animals, especially birds.
  • For more information about West Nile virus in a person's community, contact should be made with local public health officials for updated information.

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