West Nile Virus (WNV) PCR - blood specimen
- LIS Mnemonic: WNVPCR
Collect
Lavendar (EDTA)
Volume Required
4-7 ml
Minimum Required
4 ml
Transport
Transport blood in a timely fashion (preferrably within 8 hours of collection) at room temperature to the Clinical Virology Laboratory.
Processing
Other acceptable specimens include CSF, serum and tissue submitted in viral transport medium.
Unacceptable conditions
Clotted specimens
Days Performed
Daily
Reported
Same day
Reflex Testing
N/A
CPT
87798
Methodology
Amplification and detection of WNV RNA envelope gene region using TaqMan real-time PCR technology. This test is performed pursuant to an agreement with Roche Molecular Systems, Inc.
Interpretation
If positive, results are reported as West Nile virus RNA detected.
Reference Values
Negative or no West Nile virus RNA detected
Remarks
Clinical Utility: Approximately 80% of infections are asymptomatic. If disease, influenza-like illness with fever, rash, conjunctivitis, retrobulbar pain, and lymphadenopathy. In <15% of cases, acute aseptic meningitis or encephalitis characterized by long-term muscle pain and weakness in limbs. The mortality rate is 3 to 15%, mostly in patients over 50 years of age. Diagnosis is based on serologic tests and detection of viral RNA by PCR. Viremia in humans is typically low, of short duration, and often resolves before symptom onset, making PCR of blood less practical for WNV diagnosis. PCR of CSF can be beneficial and should be done in cases of central nervous system disease, but is less sensitive (60% in immunocompetent patients with CNS disease at time of clinical presentation) than serological assays. PCR of blood or CSF should not be ordered alone, but in conjunction with antibody assays for the detection of IgM and IgG to WNV. WNV-specific IgM can be detected in CSF within 3 to 5 days of clinical illness and in serum usually by day 6 of illness. IgG generally appears about 5 days after IgM. Convalescent serum specimens should be collected at least 2 weeks after the collection of the acute-phase serum when looking for seroconversion of IgG antibody. Antibodies to other Flaviviruses, such as dengue virus, St. Louis encephalitis (SLE) virus, yellow fever voris or prior yellow fever virus vaccine can cross-react with serologic tests for WNV.
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