Ask the experts
I was at a barbecue last weekend and got totally bit up by mosquitoes. This week, I've started to feel fatigued, like I might be getting the flu. Then I read in the newspaper that county health officials have detected West Nile Virus in our area. Could I have West Nile? How does a doctor diagnose West Nile virus?
Doctor's response
The diagnosis of West Nile virus infection is confirmed with a blood or cerebrospinal fluid (CSF) test to detect WNV-specific IgM antibodies. A CSF test requires a lumbar puncture (spinal tap) to obtain a specimen. IgM antibodies represent recent infection and are usually detectable during active or recent infection within three to eight days after infection, but a negative test within eight days should still be repeated if WNV infection is truly suspected. Unfortunately, WNV IgM antibodies can persist for three months or more, so the test may be positive from a prior infection, or a positive test may be due to cross-reactivity with antibodies to other flaviviruses. Therefore, a positive WNV IgM antibody must be confirmed by much more specialized testing by CDC.
WNV-specific IgG antibodies appear soon after the IgM antibodies, and remain present for life, so testing for these antibodies is not helpful for diagnosis of new infection. However, it can help sort out past infection from new infection when a person lives in an area where WNV is active or has been exposed. For example, a positive IgG with a negative IgM suggests no current or active WNV infection. This may help decide whether other causes of illness could be considered.
For more information, read our full medical article on West Nile virus.
Health Solutions From Our Sponsors
Johnston, B. Lynn, and John M. Conly. "West Nile Virus - Where Did It Come From and Where Might It Go?" Can J Infect Dis. 11.4 July-Aug. 2000: 175-178. <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2094770/>.
Kennedy, Kristy. "Calming West Nile Fears." American Academy of Pediatrics. Sept. 2002. <http://www.aap.org/family/wnv-sept02.htm>.
Klee, A.L., B. Maldin, B. Edwin, et al. "Long-Term Prognosis for Clinical West Nile Virus Infection." Emerging Infectious Diseases 10.8 (2004): 1405-1411. <https://wwwnc.cdc.gov/eid/article/10/8/03-0879_article>.
United States. Centers for Disease Control and Prevention. "Long-Term Prognosis for Clinical West Nile Virus Infection." <http://www.cdc.gov/ncidod/Eid/vol10no8/03-0879.htm#table3>.
United States. Centers for Disease Control and Prevention. "2012 West Nile Virus Update: As of August 21." Aug. 24, 2012. <http://www.cdc.gov/ncidod/dvbid/westnile/index.htm>.
United States. Centers for Disease Control and Prevention. "Update: West Nile virus screening of blood donations and transfusion-associated transmission -- United States, 2003." MMWR Morb Mortal Wkly Rep 53.13 Apr. 9, 2004: 281-284.
United States. Centers for Disease Control and Prevention. "West Nile, a Pregnancy Danger?" Feb. 28, 2004. <https://www.medicinenet.com/script/main/art.asp?articlekey=31127>.
United States. Centers for Disease Control and Prevention. "West Nile Virus." Aug. 8, 2011. <http://www.cdc.gov/Features/WestNileVirus/>.
United States. Centers for Disease Control and Prevention. "West Nile Virus (WNV) Activity Reported to ArboNET, by State, United States, 2011." Aug. 16, 2011. <http://www.cdc.gov/ncidod/dvbid/westnile/Mapsactivity/surv&control11MapsAnybyState.htm>.
United States. Centers for Disease Control and Prevention. "West Nile Virus, Pregnancy and Breastfeeding." Feb. 25, 2010. <http://www.cdc.gov/ncidod/dvbid/westnile/qa/breastfeeding.htm>.
