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West Nile Virus
 
The mild, flu-like version is often called West Nile fever. West Nile virus is a type of organism called a flavivirus and is similar to many other mosquito-borne viruses, including Japanese encephalitis (which is found in Asia). Researchers believe the virus is spread when a mosquito bites an infected bird and then bites a person.

Incidence; Risk Factors
Data from the outbreak in Queens, New York suggested that although 2.6% of the population was infected, only 1 in 5 infected people developed mild illness, and only 1 in 150 infected people developed brain inflammation (meningitis or encephalitis). The risk of disease decreases as the weather becomes colder and mosquitos die off.

Signs & Symptoms
Although many people are bitten by mosquitos that carry West Nile virus, most do not know they've been exposed. Few people develop severe disease or even notice any symptoms at all. Diagnostic tests that may be used if West Nile virus is suspected include the following:
  • CBC -- 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
  • Head MRI scan -- may show evidence of inflammation (in about one-third of patients).
This is considered the gold standard for diagnosis. Rarely, a sample of blood or CSF may be sent to a lab to be cultured to evaluate the presence of West Nile virus. However, these methods can provide false negative results.

Research trials are under way to determine whether ribavirin, an antiviral drug used to treat hepatitis C, may be helpful. For patients with severe cases of West Nile virus infection, the outlook is more guarded. Complications from mild West Nile virus infection are extremely rare but include permanent brain damage or muscle weakness (sometimes similar to polio), and death.
 
West Nile Virus is linked to:
 
Muscle Pains (Myalgia)
Pregnancy-Related Issues
Low Back Pain