Serological Test Differentiates Zika from Dengue Infections

Zika virus (ZIKV) is an emerging mosquito-transmitted flavivirus currently causing large epidemics in South and Central America as well as in the Caribbean, presenting a global public health emergency.

Zika is increasingly posing a risk in other parts of the world and it is difficult to differentiate clinically from infections with dengue and chikungunya viruses, which are endemic in the same geographical regions. In laboratory testing, serology is an important supplement to direct detection and provides a much longer diagnostic window.

European scientists led by those at the Institute for Experimental Immunology analyzed serum samples from 27 patients who had tested positive for ZIKV RNA by reverse transcription polymerase chain reaction (RT-PCR); Samples from a further 85 patients had been pre-characterized by EUROIMMUN’s anti-ZIKV indirect immunofluorescence assay based on whole virus antigen, showing reactivity for anti-ZIKV immunoglobulin M (IgM) and/or IgG; 26 travelers returning from endemic area; and 59 residents in ZIKV-endemic areas. Anti-Zika Virus IgM and IgG enzyme-linked immunosorbent assay ELISA (EUROIMMUN) were tested.

In 17 RT-PCR confirmed Zika specimens collected at least six days after symptom onset, the ELISA sensitivity amounted to 59%, for IgM, 88% for IgG and 100% for IgM/IgG. In the suspected Zika cases, the combined sensitivity was 90%. In an additional investigation using samples from 31 patients with RT-PCR confirmed Zika virus infections (follow-up samples taken 7-10 days after positive RT-PCR result); the ELISA demonstrated a sensitivity of 100% for IgM/IgG. The specificity of the ELISA with respect to the blood donors was 99.8%. Cross reactivity with high-level anti-dengue virus antibodies was not detectable. Among 252 patients with potentially cross-reactive antibodies, overall anti-Zika positive rates were 0.8% for IgM and 0.4% for IgG.

The authors concluded that the ELISA provided exceptionally high specificity and avoids the cross reactivity typically associated with tests based on whole virus antigens or viral glycoproteins. The anti-Zika virus ELISA is suitable for acute diagnostics as well as for monitoring purposes, e.g., in prenatal diagnostics, screening of donated blood and epidemiological studies. With its high-throughput format and automatability, the ELISA can be employed in routine laboratories in endemic settings. The study was published on December 16, 2016, in the journal Eurosurveillance.