Types of Zika Virus Tests
- Diagnostic testing for Zika virus infection can be accomplished using both molecular and serologic methods.
- Testing is available through commercial laboratories, many state health departments, and the Centers for Disease Control and Prevention.
- Contact your state health department for more information or to facilitate testing.
The FDA has issued Emergency Use Authorization (EUA)External for a number of diagnostic tests used to diagnose Zika virus infection. Information and documentation for these diagnostic assays, including factsheets, manufacturer instructions and package inserts are available on their Emergency Use Authorizations website.External
Nucleic acid test, or NAT, is a generic term referring to all molecular tests used to detect viral genomic material. NAT assays are the preferred method of diagnosis because they can provide confirmed evidence of infection. Despite the specificity of molecular testing, false positive NAT results have been reported in rare cases and may depend on the type of NAT assay performed and patient population (i.e., limited or no prevalence of viral transmission) being tested. This problem can be exacerbated when Zika virus testing is performed on patient populations not recommended in the Zika testing algorithms.
Due to the temporal nature of Zika virus RNA in serum and urine, a negative NAT does not exclude recent Zika infection. For this reason, Zika virus immunoglobulin (Ig) M antibody testing is recommended in certain situations. IgM levels are variable, but generally are positive starting near day 4 after onset of symptoms and continuing for up to 12 weeks post symptom onset or exposure, but may persist for months to years. Zika virus antibody testing is also complicated by cross-reactivity with other flaviviruses which may make conclusive determination of which flavivirus is responsible for the person’s recent infection difficult. With IgM antibody testing, false-positive results are more common than with NAT and can occur due to non-specific reactivity or cross-reactivity with other flaviviruses.
Plaque reduction neutralization tests (PRNT) are quantitative assays that measure virus-specific neutralizing antibody titers. PRNTs can resolve false-positive IgM antibody results caused by non-specific reactivity and at times help identify the infecting virus. While most state health departments and many commercial laboratories perform dengue and Zika virus NAT and IgM antibody testing, confirmatory neutralizing antibody testing using PRNT is currently only available through a limited number of state health departments and CDC. If Zika virus IgM antibody testing is positive and definitive diagnosis is needed for clinical or epidemiologic purposes, confirmatory PRNT should be performed against Zika and other flaviviruses endemic to the region where exposure occurred. PRNT may not discriminate between flaviviruses antibodies during the acute illness, especially following secondary flavivirus infections. Consequently, in areas with high prevalence of dengue and Zika virus neutralizing antibodies, PRNT may not confirm a significant proportion of IgM positive results. Therefore, such jurisdictions should make informed decisions about the utility of PRNT confirmation of IgM results depending on the prevalence of dengue and Zika virus neutralizing antibodies and observed performance of PRNT to confirm IgM test results.
CDC Developed Zika Diagnostic Tools
Trioplex Real-time RT-PCR Assay
The Trioplex rRT-PCR is a laboratory test designed to detect Zika virus, dengue virus, and chikungunya virus RNA. The Food and Drug Administration (FDA) has authorized the use of this test under an Emergency Use Authorization (EUA). More information on the Trioplex rRT-PCR assay can be found on the Lab Guidance webpage.
- Zika Virus – Trioplex Real-Time RT-PCR Assay Testing Instructions:
The Zika IgM Antibody Capture Enzyme-Linked Immunosorbent Assay (Zika MAC-ELISA) is used for the qualitative detection of Zika virus IgM antibodies in serum or cerebrospinal fluid; however, due to cross-reaction with other flaviviruses and possible nonspecific reactivity, results may be difficult to interpret. Consequently, presumed positive, equivocal, or inconclusive tests must be forwarded for confirmation by neutralization testing (PRNT). Additionally, IgM testing cannot be relied upon to distinguish between recent or distant infection.
Resources for US Laboratories
- EUA-specific CDC Zika MAC-ELISA Instructions
English Cdc-pdf[PDF – 101 pages]External