West Nile Virus
المؤلف:
Mary Louise Turgeon
المصدر:
Immunology & Serology in Laboratory Medicine
الجزء والصفحة:
5th E, P257-258
2025-08-23
401
Etiology
West Nile virus (WNV) is a member of the Japanese encephalitis virus group of flaviviruses that cause febrile illness and encephalitis in human beings. WNV is a mosquito-borne pathogen.
Epidemiology
The virus has been in the United States since at least the summer of 1999. Figure 1 shows the U.S. distribution of WNV in 2011. If WNV infection is reported to the CDC from any area of a state, the entire state is shaded.
Fig1. Distribution of West Nile virus activity in the United States reported to CDC’s ArboNET system, by state, United States, 2011 (as of 11/1/2011). The map shows the distribution of nonhuman activity (light green) and human infections, including PVDs (dark green). If WNV infection is reported from any area of a state, that entire state is shaded. (From Centers for Disease Control and Prevention, Atlanta [http://www.cdc. gov/ncidod/dvbid/westnile/Mapsactivity/surv&control11MapsAnybyState. htm].)
Signs and Symptoms
West Nile virus infection is characterized by fever, headache, fatigue, aches, and sometimes a rash. Illness can last from a few days to several weeks.
Diagnostic Evaluation
Historically, flavivirus infections have been diagnosed by serologic tests or virus isolation. IgM antibody is evident in most infected patients 7 to 8 days after the onset of symptoms. IgM antibody has been shown to persist for longer than 500 days in approximately 60% of cases. Most patients demonstrate IgG antibody in 3 to 4 weeks after infection.
Several molecular techniques are available for diagnosis. Molecular detection of WNV is used for prevention of trans mission by blood transfusion and transplantation. Laboratory diagnosis of WNV infection is generally accomplished by testing of serum or CSF to detect virus-specific IgM and neutralizing antibodies.
Four FDA-approved WNV IgM ELISA kits from different manufacturers are commercially available in the United States. According to the package inserts, each of these kits is indicated for use on serum to aid in the presumptive laboratory diagnosis of WNV infection in patients with clinical symptoms of meningitis or encephalitis. The package inserts also state that all positive results obtained with any of the commercially available WNV test kits should be confirmed by additional testing at a state health department laboratory or by the CDC.
In fatal cases, nucleic acid amplification, histopathology with immunohistochemistry and virus culture of autopsy tis sues can also be useful. Only a few state laboratories or other specialized laboratories, including those at the CDC, can carry out this specialized testing.
Treatment and Prevention
There is no specific treatment for WNV infection. In patients with milder disease, symptoms resolve over time, although even healthy people have been sick for several weeks. In patients with more severe disease, hospitalization is usually required for supportive treatment, including IV fluids.
Prevention consists of avoiding mosquito bites.
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