What are the odds a doctor could miss- diagnose it altogether ? Yes. You can check WNV antibodies. Usually correlates with a positive spinal fluid but in my experience has been more sensitive to check for in the serum vs. spinal fluid.
It is fairly easy to misdiagnose it if the doctor is not thinking about it. It also presents in many different degrees of severity and can mimic multiple other unrelated illnesses. West Nile virus (WNV) testing is used to determine whether someone is currently or has recently been infected with the WNV. Testing of symptomatic and seriously ill patients can help distinguish WNV from other conditions (such as bacterial meningitis) causing similar symptoms that may be treated. WNV testing also is used to screen units of blood for the virus and to track its spread through a community and across the country. Detecting the presence of WNV in the community can alert health providers and promote prevention measures.
Testing involves either a measurement of WNV antibodies (specific proteins created by the body鈥檚 immune system in response to a WNV infection) or of WNV nucleic acid (genetic material from the virus itself).
Antibody Testing
There are two types of WNV antibodies: IgM and IgG. IgM antibodies are the first to be produced by the body in response to a WNV infection. They are present in most individuals within 8 days of the initial exposure. Antibody titers continue to rise for a short time period and then will taper off. Eventually, after several months, the level of IgM falls below detectible levels.
Until recently, IgM WNV antibody testing was labor-intensive and not well standardized from lab to lab. This issue has been largely resolved by the introduction of two commercial IgM WNV antibody-capture assays that can be used as an initial test on symptomatic individuals. These tests are standardized and easier to perform but, like the methods before them, they may be positive both with WNV and with any related flaviviruses (viruses in the same family, such as St. Louis Encephalitis virus and Japanese Encephalitis virus). Therefore, positive WNV IgM tests must be confirmed by another method before a diagnosis is established and reported to the Centers for Disease Control and Prevention.
If the IgM test is negative, but symptoms and clinical signs still suggest WNV, the test may be repeated on a new specimen collected a few days later.
IgG WNV antibody testing can be used, along with IgM testing, to help confirm the presence of a recent or previous WNV infection. If the IgG test is positive, then another convalescent blood sample may be collected and tested a couple of weeks later to determine whether the amount of WNV IgG antibody (the titer) is rising, falling, or stable.
If someone who has received donated blood or an organ transplant within the previous month becomes ill and tests positive for WNV, the blood or organ is traced back to its donor, who is then tested for IgM and IgG WNV antibodies to determine whether they are the source of the recipient鈥檚 WNV. If a breastfeeding baby contracts WNV, the mother will likely be tested to determine whether the infection may have passed to the baby through the mother鈥檚 milk (a rare but documented event).
Since the majority of patients who become infected with WNV have no symptoms and no associated health problems, antibody testing is not used as a general screening test on asymptomatic people.
Nucleic Acid Testing
Nucleic acid testing involves amplifying and measuring the West Nile virus鈥檚 genetic material to detect the presence of the virus in blood or tissue. While it can specifically identify the presence of WNV, there must be a certain amount (number of copies) of virus present in the sample in order to detect it.
Since humans are incidental hosts of WNV (birds are the primary hosts), virus levels in humans are usually relatively low and do not persist for very long. Nucleic acid testing is most useful as a screen for WNV in donated units of blood and for testing birds and mosquito pools to detect the presence and spread of WNV in the community. It is possible to determine that WNV has spread to a particular area and is in the bird and mosquito population before any human cases are identified. This gives the community health services an opportunity for prevention by alerting people to its presence and the need for preventative measures, such as the use of bug repellents, limiting exposure to mosquitoes at dusk and dawn, and community spraying for mosquitoes.
It also may be useful when ordered post mortem on a patient鈥檚 blood or tissues to determine whether WNV may have caused or contributed to the patient鈥檚 death. Yes there are specific tests. |
