Validation of serological and molecular methods for diagnosis of zika virus infections

The laboratory confirmation of Zika virus (ZIKV) infection, and the differential diagnosis from other flavivirus infections such as dengue virus (DENV), often requires the use of several diagnostic test types. Cross-reactions and secondary infections complicate the serological diagnosis and specific viral RNA detection assays are often needed for confirming the diagnosis. The aim of this study was to validate serological and molecular methods for diagnosing ZIKV infection. This included the evaluation of a ZIKV RT-qPCR assay for diagnostics that was previously set up for research use and to compare the ZIKV, DENV and TBEV EIA methods. External and in-house controls and pre-characterized sample panels were tested, and also automated and manual nucleic acid extraction methods were compared. A total of ten Finnish traveler patients were diagnosed with acute ZIKV infection during 2015-2017 including one suspected dual DENV and ZIKV infection. These samples along with panels of DENV and tick-bome encephalitis virus (TBEV) infections were used to test the cross-reactive properties of ZIKV, DENV and TBEV IgM assays. Additionally, the diagnosed acute ZIKV patient samples were tested using commercially available diagnostic DENV NS1 antigen assay and a ZIKV NS1 antigen assay intended for research use. The ZIKV RT-qPCR assay was demonstrated to be both specific and sensitive (one genome per reaction) and suitable for routine diagnostic use utilizing automated nucleic acid extraction. Of the tested IgM tests the NS1 antigen-based ZIKV IgM (Euroimmun) assay performed with least cross -reactivity with a specificity of 97.4%. The DENV IgM assay (Focus Diagnostics) had specificity of only 86.1%. The results are in line with previous studies and additionally highlight that also acute TBEV patients may give a false positive test result in DENV and ZIKV IgM assays.