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Researchers Develop Assay to Distinguish Zika From Other Flaviviruses

NEW YORK (360Dx) – An international team of researchers has developed an ELISA-based test capable of distinguishing between Zika virus infection and infection by other flaviviruses like dengue.

In a study published this week in Proceedings of the National Academy of Sciences, the test detected Zika infection with a sensitivity of roughly 92 percent and a specificity that ranged between 80.4 percent and 95.9 percent depending on the composition of the control group being studied.

This performance, along with the test's ease of use and low cost (around $0.25 per test for materials), suggest that it could prove useful for detecting "recent and past Zika infections for surveillance, seroprevalence studies, and intervention trials," the study authors wrote.

As cases have exploded throughout the Americas in recent years, Zika has become a significant public health problem. As the authors noted, in pregnant women infections can lead to birth defects like microcephaly, while in adults infection with the virus has been linked with Guillain Barré syndrome.

Effective diagnostics are needed to help monitor Zika infections and develop vaccines to the disease. Developing such tests has proven challenging, however. For instance, while a number of PCR-based tests exist, "their use is limited to the narrow window when viral RNA is detectable in body fluids," the authors wrote, adding that "this is highly variable among patients and subject to reporting error."

Antibody-based tests, meanwhile, have trouble distinguishing between Zika and other flaviviruses, most notably dengue. Last month, Copenhagen-based BluSense Diagnostics announced plans to release next year a combinate Zika-dengue immunoassay capable of distinguishing between the two.

In previous work, the PNAS researchers looked at 119 monoclonal antibodies isolated in patients infected with only Zika and with Zika and dengue, finding that a number of the antibodies isolated from patients with just Zika infections were specific to that disease. They also identified two sites on the Zika nonstructural protein 1 (NS1) that the Zika-specific antibodies recognized and that were not recognized by antibodies that cross-reacted with both Zika and dengue antigens. They used one of the antibodies, ZKA35, to develop the blockade-of-binding ELISA assay tested in the PNAS study.

That study looked at 158 patients with Zika infections confirmed by PCR, 171 with primary or secondary dengue infections, and 540 patients who were either healthy or infected by other flaviviruses or other viruses. Running the samples at laboratories in five countries (Nicaragua, Brazil, Italy, United Kingdom, and Switzerland), the researchers found that the test scored 91.8 percent of the Zika infected patients as positive and 88.9 percent of the dengue patients as negative, suggesting an ability to discriminate between these two infections. Adding the 540 additional controls to the study raised the test's specificity to 95.9 percent.

The findings, the authors wrote, suggest the assay could be "a timely solution for Zika surveillance, seroprevalence studies, and intervention trials."