Brief Description

MIA testing for West Nile and St. Louis encephalitis viruses (flavivirus)

FA testing for EEE, WEE, and Calif/LaCrosse virus

NOTE:  All specimens received for Arbovirus serology will be tested against antigens of the Flavivirus group, which include West Nile Virus (WNV) and St. Louis Encephalitis (SLE).

Laboratory Unit



Microparticle Immunoassay, Fluorescent Immunoassay

IgM antibody detection on single acute, convalescent serum or CSF utilizing MIA (Microsphere Immunoassy).

Note: Testing for Eastern Equine Encephalitis (EEE), Western Equine Encephalitis (WEE), and LaCrosse/California Encephalitis Group is available only after consultation with the West Nile Virus Program (573-751-6113 or (toll-free) 1-866-628-9891).

Note: Due to low specificity, IgG antibody tests are not useful in the diagnosis of acute WNV infection. An IgG positive test result, either alone or in conjunction with an IgM negative test, is not diagnostic for acute infections and is NOT considered a case of WNV.  For this reason, IgG serology for WNV has been discontinued at the MSPHL.

Specimen Collection

Virus Serology Kit

The ideal timing to collect acute serum is 3 to 10 days after onset of symptoms.

Collect CSF as soon as possible after onset of symptoms.

Collect serum in a redtop Vacutainer tube.  Serum is the preferred specimen but whole blood will be accepted.

Whole blood may be sent if no method is available for removing the serum.

At least 1 ml of serum and 1.5 ml of CSF is required for serological testing.


Store refrigerated until transport

Acceptable Specimen Type(s)

Blood, Serum, CSF 

Test Request Form(s)

Possible Results

Serum and CSF:  All serum specimens will be tested against an IgM antibody panel that includes WNV and SLE by MIA.

If indicated, EEE, WEE, and LaCrosse/California will be performed by Fluorescent Antibody testing.

CSF specimens will be tested for WNV and SLE IgM antibodies only.

Upon completion of testing the results will be mailed to the submitter.

IgM Serology by MIA:

Positive (CSF) - Indicates recent infection.

Positive (Serum) - Indicates infection.*

Nonspecific - Results of borderline significance (Convalescent specimen required for proper interpretation). 

Negative - Results fail to indicate an infection with WNV or SLE.

* West Nile Virus IgM antibody may remain for more than one year.  Thus it will be difficult to determine if a positive IgM (from serum) is from an acute WNV infection. In this case clinical correlation is required to determine infection. 

Reference Range

Antibody so specified arbovirus not identified.

Unacceptable Conditions

Specimen not identified

Interfering Substances


Result Reported

3 to 10 days after receipt of specimen.  May vary during high and low volume testing periods.



CPT Codes




Additional Information