Being Diagnosed, How They Know.

You have been getting very frequent and intense headaches recently. You are coming down with a fever and think its a good time to visit your physician. You've called, made an appointment, and by the time you go, you feel much worse.

Your doctor is going to immediately start putting together the puzzle of symptoms, signs, history, and any other pertinent key factors.

Most cerebral viral maladies all have similar symptoms, such as encephalitis. So the ways of determining what is causing these handful of symptoms, is similar. It is called a lumbar puncture to test the cerebrospinal fluid. This is done with a sizable needle and isn't usually a fun procedure.

Fig. 1: Lumbar Puncture

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You have sat through it though, and they are now looking at your test results. What they were looking for were antibodies, or proteins our bodies produce after being exposed to a pathogen. These antibodies are specific to diseases, and for West Nile Virus, they know exactly what to look for. This is an "IgM" antibody that is specifically produced against the WNV antigen. After IgM antibodies are made, then IgG antibodies, which are long term are produced. So if a lab test is performed and only IgG antibodies (long term) are found, this is only evidence of previous infection from WNV, not a current episode of it, as that would produce IgM specific antibodies.

Fig. 2: West Nile Virus, Antibody, and Vector

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There are other tests, such as polymerase chain reaction, that are tested against CSF, blood and tissue samples early on in the disease. Currently though, the antibody test from cerebrospinal fluid is the fastest, most accurate, and best at determining between current and past infection.

Your doctor calls you after the lab results come back. He has bad news, but its good as its treatable. He lets you know you have a positive antibody test for a current West Nile Virus infection and will be treating you accordingly to reduce your symptoms and help with your wellness. We will discuss what those treatments are in future blog posts.

References:
Barzon, L., Pacenti, M., Ulbert, S., & Palu, G. (2015). Latest developments and challenges in the diagnosis of human West Nile virus infection. Expert Review of Anti Infective Therapy, March 2015