Rapid testing for West Nile virus (WNV) RNA (lineage 1 and lineage 2) using serum specimens
An adjunctive test to serology for detection of early WNV infection (ie, first few days after symptom onset)
This assay should not be used for screening asymptomatic individuals and should only be used to test patients with signs and symptoms of WNV disease.
The following algorithms are available in Special Instructions:
Real-Time Polymerase Chain Reaction (PCR)
Arbovirus
Flavivirus
Mosquito Borne Encephalitis
Viral encephalitis
West Nile PCR
West Nile Virus (WNV)
WNV PCR
The following algorithms are available in Special Instructions:
Serum
Collection Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Submission Container: Sterile container
Specimen Volume: 0.5 mL
Collection Instructions:
1. Centrifuge and aliquot the serum into a sterile container within 6 hours of collection.
2. Label specimen as serum.
If not ordering electronically, complete, print, and send a Microbiology Test Request (T244) with the specimen.
0.3 mL
Gross hemolysis | Reject |
Heat-inactivated specimen | Reject |
Specimen Type | Temperature | Time | Special Container |
---|---|---|---|
Serum | Refrigerated (preferred) | 7 days | |
Frozen | 7 days |
Rapid testing for West Nile virus (WNV) RNA (lineage 1 and lineage 2) using serum specimens
An adjunctive test to serology for detection of early WNV infection (ie, first few days after symptom onset)
This assay should not be used for screening asymptomatic individuals and should only be used to test patients with signs and symptoms of WNV disease.
The following algorithms are available in Special Instructions:
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%) results 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 are at particularly high risk.
Laboratory diagnosis is best achieved by demonstration of specific IgG- and IgM-class antibodies in serum specimens. However, polymerase chain reaction (PCR) testing can be used to detect WNV RNA in serum, whole blood, and urine specimens from patients with recent WNV infection (ie, 3-5 days following infection) when specific antibodies to the virus are not yet present. It may also be useful for patients who are immunocompromised when an antibody response is minimal or absent. Finally, PCR can also be useful for supporting a serologic diagnosis, given the known cross-reactivity of WNV serology with other flaviviruses.
Studies indicate that whole blood testing by PCR may provide higher sensitivity when testing patients with acute WNV disease (up to 87%) compared to serum, plasma, urine, and cerebrospinal fluid testing.(4) However, viral RNA may be detected for a longer period of time (> or =10 days after symptom onset) in urine than in other sources.(5) Serum testing offers lower sensitivity (26%) but may be used when it is the only specimen type available.
Negative
A positive result indicates the presence of West Nile virus (WNV) RNA and is consistent with early WNV infection.
The sensitivity of the assay is very dependent upon the time of illness onset in which the specimen is collected. Polymerase chain reaction testing has the greatest utility when used within the first few days of symptom onset.
Whole blood rather than serum has been shown to provide increased sensitivity for detecting West Nile virus (WNV) RNA.
A negative test does not exclude infection with WNV. Therefore, the results obtained should be used in conjunction with clinical findings and serologic test results 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.
The following validation data supports the use of this assay for clinical testing.
Accuracy/Diagnostic Sensitivity and Specificity:
Accuracy studies were performed by testing negative clinical specimens with whole viral genomic RNA for lineages 1 and 2 near the limit of detection (LOD) and yielded greater than or equal to 97% sensitivity and specificity.
Analytical Sensitivity/Limit of Detection:
The lower LOD of this assay is 1 to 5 target copies/mcL of RNA extract for serum, urine, and spinal fluid, and 27 to 60 copies/mcL for EDTA whole blood.
Precision:
Inter-assay and intra-assay precisions are 100%.
Specificity:
A panel of 42 organisms that can be found in the specimen types acceptable for this assay, as well as closely-related viruses (eg, Dengue types 1-4, Japanese encephalitis virus, hepatitis E virus, Murray Valley encephalitis virus, St. Louis encephalitis virus, tick-borne encephalitis virus, yellow fever virus, Zika virus) and those that can cause a similar clinical syndrome were tested by this assay. No cross-reacting positive results were noted.
Reportable Range:
This is a qualitative assay and the results are reported as either negative or positive for targeted West Nile virus.
2. Colpitts TM, Conway MJ, Montgomery RR, Fikrig E: West Nile virus: Biology, transmission, and human infection. Clin Microbiol Rev. 2012 Oct;25(4):635-648
3. Centers for Disease Control and Prevention (CDC), National Center for Emerging and Zoonotic Infectious Disease (NCEZID), Division of Vector-Borne Diseases (DVBD): West Nile Virus: Information for Healthcare Providers. CDC; Reviewed December 10, 2018. Accessed December 14, 2020. Available at www.cdc.gov/westnile/healthcareproviders/index.html
4. Lustig Y, Mannasse B, Koren R, et al: Superiority of West Nile virus RNA detection in whole blood for diagnosis of acute infection. J Clin Microbiol. 2016 Sep;54(9):2294-2297
5. Barzon L, Pacenti M, Franchin E, et al: Excretion of West Nile virus in urine during acute Infection. J Infect Dis. 2013 Oct;208(7):1086-1092
Monday through Friday
This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.
87798
Test Id | Test Order Name | Order LOINC Value |
---|---|---|
WNVS | West Nile Virus RNA, PCR, Serum | 32361-8 |
Result Id | Test Result Name |
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|
---|---|---|
608436 | West Nile Virus RNA, PCR, Serum | 32361-8 |