Zika Virus Test Will Make Blood Transfusions Safer For Pregnant Women

Until now, diagnosing Zika has been hit-or-miss. But with the virus fully sequenced, that's about to change

An Aedes Aegypti mosquito, likely carried of Zika, is studied in a lab — (REUTERS)
Sep 05, 2016 at 11:00 AM ET

We still know surprisingly little about Zika virus, especially when it comes to diagnosing the disease. A mosquito-borne illness that has already infected hundreds of thousands worldwide, Zika is often harmless — 80 percent of patients never even know they have it — but some studies suggest the virus is linked to microcephaly, a debilitating birth defect. The most frustrating part? We’re still not exactly sure how to determine that a virus is indeed Zika. Right now, scientists rely on a combination of symptoms, travel records, and a vague RNA blood test to make the call.

But now, researchers have published a so-called “reference” strain of the Zika virus, which is slated to become the World Health Organization’s official strain — against which all future RNA blood tests will be conducted. Although the results had not been expected before mid-October WHO fast-tracked the project, in response to the growing need for a reliable, standardized blood test.

“WHO’s go-ahead before its expert committee meeting in October reflects the urgent need for researchers and companies to access valid reference material to diagnose Zika virus infection,” said coauthor Sally Baylis of the Paul-Ehrlich-Institut in Germany, in a statement. “This will facilitate the development of sensitive, better performing tests to detect Zika in patients.”

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The reference strain itself is an impossibly long string of 10,769 letters, which precisely identifies the unique genetic identity of the most utterly average Zika virus available. That’s how reference standards work in most infectious diseases — WHO maintains a database of the DNA or RNA of standard bugs, so that researchers can compare their own samples against the ones on file. If there’s a match, healthcare providers can be confident that they’re diagnosing the disease correctly. If not, they can head back to the drawing board with similar, if less elated, confidence.

To create the worldwide standard Zika sequence, researchers first isolated a Zika strain known as PF13/251013-18 from a blood sample obtained from a French Polynesian patient in 2013. They then scanned multiple RNA sequences from the sample, and used genetic databases to help them decide which candidate sequence would be best suited for its purpose as a broad Zika reference. The final string of RNA is most closely related to strains of Zika currently ravaging the Pacific, Central and South America, and the Caribbean, although it could also help diagnose less common strains.

Crucially, the reference strain will also help detect Zika in unrelated blood samples, such as blood transfusions. Until now, there was no reliable way to ensure that a pregnant woman receiving a blood transfusion would not end up contracting Zika from the lifesaving intervention itself. Now, doctors will be able to compare a candidate blood sample with the WHO standard virus, to ensure that the blood is safe. “Diagnosis of acute ZIKV infection relies upon the detection of virus RNA in plasma, urine, and other body fluids,” the authors write.
In order to implement robust diagnostic testing methods, a candidate World Health Organization (WHO) reference material (international standard), intended to be used for the quantitation of ZIKV RNA and evaluated in an international study, was developed.”