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Unit Code 86197:
West Nile Virus (WNV) RNA Detection by Rapid PCR

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Useful For

Rapid testing for WNV RNA

 

As an adjunct in the diagnosis of early WNV infection

Clinical Information

WNV is a mosquito-borne flavivirus (single stranded RNA)

that primarily infects birds, but occasionally infects horses and

humans. Until the virus infection was recognized in 1999 in birds in

New York City, WNV was found only in the Eastern hemisphere, with

a wide distribution in Africa, Asia, the Middle East and Europe.(1-3)

Most people who are infected with WNV do not experience symptoms.

It is estimated that about 20% of those who become infected will

develop West Nile fever with mild symptoms including headache,

myalgia, and occasionally a skin rash on the trunk of the body. About

1 of 150 WNV infections (<1%) result in meningitis or encephalitis.

Case fatality rates among patients hospitalized during recent outbreaks

have ranged from 4% to 14%. Advanced age is the most important

risk factor for death, and patients older than 70 years of age are at

particularly high risk.

 

Laboratory diagnosis is best achieved by demonstration of specific

IgG and IgM class antibodies in serum or cerebrospinal fluid (CSF)

specimens (#84186 "West Nile Virus [WNV] Antibody, IgG and IgM,

Serum" or #88680 "West Nile Virus [WNV] Antibody, IgG and IgM,

Spinal Fluid").

 

The specific identification of WNV by detection of IgM in CSF is the

recommended test to document central nervous system disease,

but this test may be falsely negative in CSF collected <8 days after

the onset of symptoms. Alternatively, experiences in nucleic acid

testing for WNV RNA in blood prior to transfusion have indicated that

PCR can detect viremic target RNA from patients with known West

Nile infection when specific antibodies to the virus are not present

(ie, from 2-8 days after onset of symptoms).(4,5)

Reference Values

Negative

Positive results will be reported as WNV nucleic acid detected.

Interpretation

The likelihood of detection of WNV RNA by PCR is relatively low. In

CSF, the sensitivity is approximately 55%, and in blood, about 10%.

Specificity of the assay in either matrix is approximately 100%.(6)

Cautions

The sensitivity of the assay is very dependent upon the quality of

the specimen submitted.

 

A negative test does not exclude infection with WNV.  

Therefore, the results obtained should be used in conjunction with

clinical findings to make an accurate diagnosis.

 

This assay detects both viable and nonviable virus. Test

performance depends on viral load in the specimen and may

not correlate with cell culture performed on the same specimen.

 

Possible cross-reactivity with other flaviviruses (eg, dengue virus,

St. Louis encephalitis virus, and Japanese Encephalitis virus) has

not been assessed. 

Clinical Reference

1.   Brinton MA:  The molecular biology of West Nile Virus:  a new

      invader of the western hemisphere. Ann Rev Microbiol 2002;56:

      371-402

 

2.   Petersen LR, Marfin AA:  West Nile virus: a primer for the clinician.

      Ann Intern Med 2002;137(3):173-179

 

3.   Petersen LR, Roehrig JT:  West Nile virus:  a reemerging global

      pathogen. Emerg Infect Dis 2001;7(4):611-614

 

4.   Busch MP, Tobler LH, Saldanha J, et al:  Analytical and clinical

      sensitivity of West Nile virus RNA screening and supplemental

      assays available in 2003. Transfusion 2005;5(4):492-499

 

5.   Epstein JS:  Insights on donor screening for West Nile virus.

      Transfusion 2005;45(4):460-462

 

6.   New York City Department of Health. West Nile surveillance and

      control: an update for healthcare providers in New York City.

      City Health Information. June 2001;20(2)

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