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Encephalitis Virus Antibody Blood Test

Last updated May 11, 2018

The Encephalitis Virus Antibody Blood Test helps detect antibodies (IgM or IgG) specific to encephalitis viruses. It aids in the diagnosis of an infection by an encephalitis virus.


What are other Names for this Test? (Equivalent Terms)

  • Encephalitis Virus Ab Blood Test

What is the Encephalitis Virus Antibody Blood Test? (Background Information)

  • Encephalitis is inflammation of the brain tissue. It is often caused by infection by viruses that are transmitted by mosquitoes. These viruses are called arboviruses, which means arthropod-borne virus (mosquitoes are classified as a type of arthropod)
  • Common arboviruses that cause encephalitis include Eastern equine encephalitis virus, California encephalitis virus, St. Louis encephalitis virus, Venezuelan equine encephalitis virus, and Western equine encephalitis virus
    • Eastern equine encephalitis virus is transmitted by mosquitoes that have received the virus through contact with birds and horses. It is found in the Eastern US and Texas. This is a particularly dangerous encephalitis virus, as the death rate due to an infection is between 65% to 75%
    • The California encephalitis virus infects children in the north central US. It is transmitted by ticks as well as by mosquitoes
    • The St. Louis encephalitis virus is transmitted by mosquitoes that have received the virus through contact with birds. It occurs mainly in the south, central, and western US
    • The Venezuelan equine encephalitis virus is found mainly in Latin America, Texas, and Florida. It is transmitted by mosquitoes that have received the virus through contact with rodents and horses
    • The western equine encephalitis virus occurs mainly in California. It is transmitted by mosquitoes that have received the virus through contact with birds, squirrels, snakes, and horses
  • When the immune system encounters an invader, it rapidly produces defense proteins (antibodies) that target the invader. These antibodies recognize specific components (antigens) of that invader; e.g. proteins, cellular membrane lipids, etc.
  • Thus, the presence of an antibody specific to an encephalitis virus implies that the body has been infected by that virus either in the past, or there is currently an infection
  • There are several types of antibodies. The 2 most clinically important ones called IgM and IgG
    • IgM is produced within days of infection as part of the primary immune response. Elevated levels of IgM indicate a ‘new’ infection
    • IgG is produced several weeks after infection as part of the secondary immune response. Elevated levels of IgG indicate a chronic or past infection
  • The Encephalitis Virus Antibody Blood Test helps detect antibodies (IgM or IgG) specific to encephalitis viruses. It aids in the diagnosis of an infection by an encephalitis virus
  • The Encephalitis Virus Antibody Blood Test is performed by making dilutions of a blood sample; for example, 2-fold, 4-fold, 8-fold, and so on, and mixing each diluted sample with encephalitis virus antigens
  • Subsequent steps allow for the visualization of possible interactions between the antibodies and antigen through a reaction (such as emission of light, color change, etc.). The highest dilution in which a reaction takes place is called the titer

What are the Clinical Indications for performing the Encephalitis Virus Antibody Blood Test?

Following are the clinical indications for performing the Encephalitis Virus Antibody Blood Test:

  • Fever
  • Headache
  • Drowsiness
  • Nausea
  • Vomiting
  • Neck stiffness
  • Bulging of the fontanelle in infants
  • Sore throat
  • Altered mental status
  • Fatigue 

How is the Specimen Collected for the Encephalitis Virus Antibody Blood Test?

Following is the specimen collection process for Encephalitis Virus Antibody Blood Test:

Sample required: Blood

Process of obtaining blood sample in adults:

  • A band is wrapped around the arm, 3-4 inches above the collection site (superficial vein that lies within the elbow pit)
  • The site is cleaned with 70% alcohol in an outward spiral, away from the zone of needle insertion
  • The needle cap is removed and is held in line with the vein, pulling the skin tight
  • With a small and quick thrust, the vein is penetrated using the needle
  • The required amount of blood sample is collected by pulling the plunger of the syringe out slowly
  • The wrap band is removed, gauze is placed on the collection site, and the needle is removed
  • The blood is immediately transferred into the blood container, which has the appropriate preservative/clot activator/anti-coagulant
  • The syringe and the needle are disposed into the appropriate “sharp container” for safe and hygienic disposal

Preparation required: No special preparation is needed prior to the test.

What is the Significance of the Encephalitis Virus Antibody Blood Test Result?

A positive value for the Encephalitis Virus Antibody Blood Test is associated with a reaction taking place with a blood sample that has been diluted more than 10 times (i.e., a titer above 1:10). This may indicate:

  • Viral encephalitis caused by the identified type of virus, most commonly:
    • Eastern equine encephalitis virus
    • California encephalitis virus
    • St. Louis encephalitis virus
    • Venezuelan equine encephalitis virus
    • Western equine encephalitis virus
  • Meningoencephalitis

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

  • The Encephalitis Virus Antibody Blood Test is performed using samples taken when the individual was actively undergoing infection (acute phase) and when he/she has recovered from the infection (convalescent phase)

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider of the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

What are some Useful Resources for Additional Information?


References and Information Sources used for the Article:


Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Feb. 1, 2016
Last updated: May 11, 2018