Western Equine Encephalitis

By Metcalf, Eric 
March 22, 2017

Western Equine Encephalitis (CSF)

Does this test have other names?

Lumbar puncture

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 develop encephalitis, or inflammation of the brain. Adults are less likely to develop this complication. Horses can also become infected.

This test uses a sample of cerebrospinal fluid (CSF). This fluid surrounds 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 develop rapidly and may include:

  • Fever

  • Drowsiness

  • Fatigue

  • Dizziness

  • Weakness

  • Headache

  • Backache

  • Nausea and vomiting

  • Neck stiffness

  • Disorientation

In babies, symptoms of Western equine encephalitis 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?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your healthcare provider.

This test typically 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, it's likely you have the disease. 

How is this test done?

This test requires a sample of cerebrospinal fluid, which is taken through a lumbar puncture in your lower back. During this procedure, you either sit up and lean forward or lie down on your side. A healthcare provider inserts a needle into your spine and draws 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 inserted

  • Headache

  • Infection

  • Bleeding

  • Brain herniation, which 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, especially in children, to numb the spot where the needle will be inserted. Children may get upset about the procedure. So a healthcare provider should thoroughly explain to kids what to expect.

Providers sometimes use a CT scan to create images of the brain before a lumbar puncture. This is to check for high pressure within the skull that 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. 


March 22, 2017


Approach to the Patient with Central Nervous System Infection. Tunkel AR. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. Chap. 83. 2010, 7th ed., pp. 1183-8., Arboviral Encephalitis in North America. Halstead SB. Nelson Textbook of Pediatrics. Chap. 259. 2011, 19th ed., pp. 1141-4., Arboviruses Affecting the Central Nervous System. Bleck TP. Goldman's Cecil Medicine. Chap. 391. 2012, 24th ed., p. 2164., Western Equine Encephalitis Virus Serology. Clinical Key.

Reviewed By:  

Snyder, Mandy, APRN,Taylor, Wanda, RN, PhD