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West Nile Virus Testing

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Also known as: WNV Tests; WNV by NAAT
Formal name: West Nile Virus, IgM and IgG Antibodies and Nucleic Acid Amplification Tests

At a Glance

Why Get Tested?

To help diagnose an infection caused by West Nile virus (WNV); to determine the cause of viral meningitis or encephalitis or febrile illness that occurs during the summer season; to detect the presence of WNV and to track its spread in the community and across the United States; to screen for WNV in donated units of blood, tissues, or organs

When to Get Tested?

When you have symptoms suggesting WNV such as headache, fever, stiff neck, and muscular weakness and have been exposed to mosquitos or when you have had a diagnosis of encephalitis and/or meningitis associated with the summer season

Sample Required?

Cerebrospinal fluid collected from a spinal tap and/or a blood sample drawn from a vein in your arm

Test Preparation Needed?

None

The Test Sample

What is being tested?

West Nile virus (WNV) is an infection that is transmitted to humans primarily by mosquitoes that have bitten infected birds or other infected humans. Testing detects either the West Nile virus directly or antibodies produced in response to WNV infection in blood and/or cerebrospinal fluid (CSF).

The virus is not passed through handling or consumption of infected birds or directly from person-to-person; however, there have been rare cases of WNV being transmitted to others through blood donations, organ transplants, and from a mother to child during pregnancy, delivery, or through breast milk.

About 80% of people infected with WNV experience no symptoms. In the other 20%, it causes flu-like symptoms such as headache, fever, nausea, muscular weakness, and/or a skin rash on the back or chest. These symptoms usually resolve without treatment within a few days to a few weeks. Only about 1 in 150 people infected with WNV becomes seriously ill with an infection that affects the central nervous system. These people may experience severe symptoms such as confusion, convulsions, high fever, neck stiffness, headaches, or a coma. They may have encephalitis and/or meningitis and/or may experience muscular paralysis. This serious form of WNV is much more common in the elderly, people with weakened immune systems (immunocompromised), and individuals with underlying conditions such as diabetes or high blood pressure (hypertension). While most symptoms resolve within several weeks, some nerve damage and paralysis may linger or be permanent.

The two types of WNV testing include:

  • Antibody testing—detects either IgM or IgG class of WNV antibodies
  • Nucleic acid amplification (NAAT)—detects the genetic material (RNA) of WNV

How is the sample collected for testing?

Cerebrospinal fluid is collected from a spinal tap and/or a blood sample is drawn from a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

Common Questions

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Article Sources

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used in Current Review

(2013 June 14). West Nile Virus in the United States: Guidelines for Surveillance, Prevention, and Control. Centers for Disease Control and Prevention [On-line information]. Available online at http://www.cdc.gov/westnile/resources/pdfs/wnvGuidelines.pdf through http://www.cdc.gov. Accessed May 2014.

(© 1995–2014). West Nile Virus (WNV) Antibody, IgG and IgM, Serum. Mayo Clinic Mayo Medical Laboratory [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/84186 through http://www.mayomedicallaboratories.com. Accessed May 2014.

(Reviewed 2013 June 7). Diagnostic Testing WNV Antibody Testing. Centers for Disease Control and Prevention [On-line information]. Available online at http://www.cdc.gov/westnile/healthCareProviders/healthCareProviders-Diagnostic.html through http://www.cdc.gov. Accessed May 2014.

Gavin, M. (Reviewed 2012 August). West Nile Basics. TeensHealth from Nemours [On-line information]. Available online at http://kidshealth.org/teen/infections/bacterial_viral/west_nile.html through http://kidshealth.org. Accessed May 2014.

Murray, K. et. al. (2013). West Nile Virus, Texas, USA, 2012. Medscape Multispecialty from Emerging Infectious Diseases. 2013;19(11):1836-1838. [On-line information]. Available online at http://www.medscape.com/viewarticle/819868 through http://www.medscape.com. Accessed May 2014.

Salinas, J and Steiner, M. (Updated 2012 January 18). West Nile Virus. Medscape Multispecialty [On-line information]. Available online at http://emedicine.medscape.com/article/312210-overview through http://emedicine.medscape.com. Accessed May 2014.

Pittman, M. et. al. (2013 June 24). Recognition and Management of West Nile Virus in the ED. Medscape Multispecialty [On-line information]. Available online at http://www.medscape.com/viewarticle/804206 through http://www.medscape.com. Accessed May 2014.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Tabers Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

Petersen, L. and Marfin, A. (2002 August 6). West Nile Virus: A Primer for the Clinician. Annals of Internal Medicine Volume (137) 3:173-179 [On-line journal article]. Available online at http://www.annals.org/cgi/content/full/137/3/173 through http://www.annals.org.

(2003 September 24, Modified). West Nile Virus (WNV) Infection: Information for Clinicians. CDC, Division of Vector-Borne Infectious Diseases, West Nile Virus [On-line Fact Sheet]. Available online at http://www.cdc.gov/ncidod/dvbid/westnile/resources/fact_sheet_clinician.htm through http://www.cdc.gov.

(2003 September 10). Testing and Treating West Nile Virus in Humans. CDC, Division of Vector-Borne Infectious Diseases, West Nile Virus, Questions and Answers [On-line Information]. Available online at http://www.cdc.gov/ncidod/dvbid/westnile/qa/testing_treating.htm through http://www.cdc.gov.

(2003 July 15). Update on West Nile Virus. CDC Telebriefing Transcript [On-line News Conference]. Available online at http://www.cdc.gov/od/oc/media/transcripts/t030715.htm through http://www.cdc.gov.

(2003). Epidemic/Epizootic West Nile Virus in the United States: Guidelines for Surveillance, Prevention, and Control. CDC [On-line Guidelines]. PDF available for download at http://www.cdc.gov/ncidod/dvbid/westnile/resources/wnv-guidelines-aug-2003.pdf through http://www.cdc.gov.

Hayes, E. et. al (2004 February 27). Interim Guidelines for the Evaluation of Infants Born to Mothers Infected With West Nile Virus During Pregnancy. CDC, Division of Vector-Borne Infectious Diseases, West Nile Virus [On-line Clinical Guidelines, Published in MMWR (53) 7]. Available online at http://www.cdc.gov/ncidod/dvbid/westnile/congenitalinterimguidelines.htm through http://www.cdc.gov.

Martin, D. et. al (2000 May). Standardization of Immunoglobulin M Capture Enzyme-Linked Immunosorbent Assays for Routine Diagnosis of Arboviral Infections. Journal of Clinical Microbiology (38) 5:1823-1826 [On-line journal]. Available online at http://jcm.asm.org/cgi/content/full/38/5/1823 through http://jcm.asm.org.

(2003 July 9). FDA Clears First Test for West Nile Virus. FDA News [On-line News Release]. Available online at http://www.fda.gov/bbs/topics/NEWS/2003/NEW00920.html through http://www.fda.gov.

(2003 May). Revised Recommendations for the Assessment of Donor Suitability and Blood and Blood Product Safety in Cases of Known or Suspected West Nile Virus Infection. FDA [On-line Guidance for Industry]. Available online at http://www.fda.gov/cber/gdlns/wnvguid.htm through http://www.fda.gov.

(2002 December) Arbovirus IFA Slides. PANBIO [On-line package insert]. PDF available for download at http://www.panbio.com.au/prodinfo/I-WNV01X%20-%2004DEC02-005.pdf through http://www.panbio.com.au.

(2003 July 17, Revised). West Nile Virus IgM Capture ELISA. PANBIO [On-line package insert]. PDF available for download at http://www.panbio.com.au/prodinfo/E-WNV01M.pdf through http://www.panbio.com.au.

Bren, L. (2003 January-February). West Nile Virus: Reducing the Risk. FDA Consumer Magazine [On-line article]. Available online at http://www.fda.gov/fdac/features/2003/103_virus.html through http://www.fda.gov.

(2004 February 23). US Startled by Extent of West Nile in Blood Donors. Reuters by Yahoo! Health [On-line article]. Available online at http://health.yahoo.com/search/healthnews?lb=p&p=id%3A54298 through http://health.yahoo.com.

(2003 December 11). West Nile Virus IgM Capture ELISA. FOCUS Technologies, Package Insert [On-line information]. Available online through http://www.focusanswers.com.

(2003 June 25). Focus Submits West Nile Virus Diagnostic Kits to FDA for 510 (k) Clearance [5 paragraphs]. FOCUS Technologies [On-line Press Release]. Available online through http://www.focusanswers.com.

Pagana, Kathleen D. & Pagana, Timothy J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp. 1001-1002.

Wu, A. (2006). Tietz Clinical Guide to Laboratory Tests, Fourth Edition. Saunders Elsevier, St. Louis, Missouri. Pp. 1626.

(2007 August 28). FDA Approves Second West Nile Screening Test for Donated Blood and Organs. FDA News [On-line press release]. Available online at http://www.fda.gov/bbs/topics/NEWS/2007/NEW01691.html through http://www.fda.gov. Accessed on 9/09/07.

(2007 March 2). FDA Approves First Fully Automated Test to Screen for West Nile Virus in Blood and Tissue Donors. FDA News [On-line press release]. Available online at http://www.fda.gov/bbs/topics/NEWS/2007/NEW01578.html through http://www.fda.gov. Accessed on 9/09/07.

(2006 August 25). Recommendations for Protecting Laboratory, Field, and Clinical Workers from West Nile Virus Exposure. National Institute for Occupational Safety and Health [On-line information]. Available online at http://www.cdc.gov/niosh/topics/westnile/reclab.html through http://www.cdc.gov. Accessed on 9/09/07.

(2005 September 4). What You Need to Know about Mosquito Repellent. CDC West Nile Virus Fact Sheet [On-line information]. Available online at http://www.cdc.gov/ncidod/dvbid/westnile/mosquitorepellent.htm through http://www.cdc.gov. Accessed on 9/09/07.

(2005 September 27). West Nile Virus Fact Sheet. CDC West Nile Virus Fact Sheet [On-line information]. Available online at http://www.cdc.gov/ncidod/dvbid/westnile/wnv_factsheet.htm through http://www.cdc.gov. Accessed on 9/09/07.

(2007 August 1, Reviewed). Testing and Treating West Nile Virus in Humans. CDC Questions and Answers [On-line information]. Available online at http://www.cdc.gov/ncidod/dvbid/westnile/qa/testing_treating.htm through http://www.cdc.gov. Accessed on 9/09/07.

(2007 June 22). West Nile Virus Sequelae Can Be Long-Term. Medscape Reuters Health Information [On-line information]. Available online at http://www.medscape.com/viewarticle/558721 through http://www.medscape.com. Accessed on 9/09/07.

Murray, K. et. al. (2007 April 05). Depression after Infection with West Nile Virus. Medscape from Emerg Infect Dis. 2007;13(3): 479-481. [On-line journal article]. Available online at http://www.medscape.com/viewarticle/554199 through http://www.medscape.com. Accessed on 9/09/07.

(2007 May 1). West Nile virus. MayoClinic.com [On-line information]. Available online through http://www.mayoclinic.com. Accessed on 9/09/07.

Salinas, J. and Steiner, M. (Updated November 6). West Nile Virus. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/312210-overview through http://emedicine.medscape.com. Accessed November 2010.

Cunha, B. (Updated 2010 October 18). West Nile Encephalitis. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/234009-overview through http://emedicine.medscape.com. Accessed November 2010.

Lindsey, N. et. al. (2010 September 13). West Nile Virus Activity — United States, 2009. Medscape Today from Morbidity & Mortality Weekly Report. 2010;59(25):769-772. © 2010 Centers for Disease Control and Prevention (CDC). Available online at http://www.medscape.com/viewarticle/725089 through http://www.medscape.com. Accessed November 2010.

Mayo Clinic Staff (2010 June 26) West Nile virus. MayoClinic.com [On-line information]. Available online at http://www.mayoclinic.com/health/west-nile-virus/DS00438/METHOD=print through http://www.mayoclinic.com. Accessed November 2010.

Dugdale, D. (Updated 2010 September 15). West Nile virus. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/007186.htm. Accessed November 2010.

Neitzel, D. et. al. (2009 August 11). False-Positive Results with a Commercially Available West Nile Virus Immunoglobulin M Assay --- United States, 2008. Medscape Today from Morbidity & Mortality Weekly Report. 2009;58(17):458-460. © 2009 Centers for Disease Control and Prevention (CDC) [On-line information]. Available online at http://www.medscape.com/viewarticle/706830 through http://www.medscape.com. Accessed November 2010.

Hillyard, D. et. al. (Updated 2010 January). Arboviruses. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/Arboviruses.html?client_ID=LTD through http://www.arupconsult.com. Accessed November 2010.

(March 9, 2009) National Institute for Allergy and Infectious Diseases. West Nile Virus Diagnosis. Available online at http://www.niaid.nih.gov/topics/westNile/understanding/Pages/diagnosis.aspx through http://www.niaid.nih.gov. Accessed January 2011.

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