Western Equine Encephalitis (CSF)

Does this test have other names?


What is this test?

This test looks for the virus that causes Western equine encephalitis. This is a disease that is spread through bites from infected mosquitoes. Babies and young children who are infected are more likely to get inflammation of the brain (encephalitis). Adults are less likely to have this problem. Horses can also become infected.

This test uses a sample of cerebrospinal fluid. This fluid is around the brain and spinal cord.

Why do I need this test?

You may need this test to find out if you are infected with the virus that causes Western equine encephalitis. Symptoms can show up quickly. They may include:

  • Fever

  • Drowsiness

  • Tiredness (fatigue)

  • Dizziness

  • Weakness

  • Headache

  • Backache

  • Nausea and vomiting

  • Neck stiffness

  • Disorientation

Symptoms of Western equine encephalitis in babies include fussiness, vomiting, fever, failure to eat, and seizures.

What other tests might I have along with this test?

You may also have a blood test to check for the virus.

What do my test results mean?

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your healthcare provider what your test results mean for you.

This test measures levels of immunoglobulin M (IgM). IgM is a type of antibody that your immune system makes against the virus. If your CSF sample contains IgM antibodies, you may have the disease. 

How is this test done?

This test is done with a sample of cerebrospinal fluid. The healthcare provider takes the sample during a spinal tap (lumbar puncture) in your lower back. During this test, you either sit up and lean forward or lie down on your side. The provider puts a needle into your lower back. They draw out a sample of fluid through the needle.  

Does this test pose any risks?

Side effects of a lumbar puncture include:

  • Discomfort while the needle is put in

  • Headache

  • Infection

  • Bleeding

  • Brain herniation. This is rare but life-threatening.

What might affect my test results?

Tell your healthcare provider if you're taking medicine or have any other health conditions.

How do I get ready for this test?

Healthcare providers sometimes use local anesthesia to numb the spot where the needle will be put in. This is especially true for children. Children may get upset about the procedure. So a healthcare provider or child specialist should explain to the child what to expect.

Providers sometimes use a CT scan to make images of the brain before this test. This is to check for high pressure in the skull. High pressure could lead to brain herniation from the procedure.

Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.

Online Medical Reviewer: Chad Haldeman-Englert MD
Online Medical Reviewer: Raymond Turley Jr PA-C
Online Medical Reviewer: Tara Novick BSN MSN
Date Last Reviewed: 10/1/2022
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