new blood test can cheaply and quickly distinguish between the mosquito-borne Zika and dengue viruses, researchers reported Wednesday, giving public health officials a valuable tool to track the spread of outbreaks and prepare for the possible consequences of the different infections.
The test, which was described in the journal Science Translational Medicine, relies on a simple paper strip, and researchers hope it can eventually be purchased for less than $1. The scientists who developed the test are at work to commercialize it and production would need to be scaled up before it could be deployed widely.
Knowing which disease is spreading in an area is crucial for public health responses and research. But the Zika-dengue distinction is all the more important because Zika, unlike dengue, can cause severe birth defects and can be transmitted through sex, meaning it is vital for pregnant women to know which virus they have and for their sexual partners to identify their infections as well.
The problem is that Zika and dengue are similar; with some tests, the viruses “cross-react,” meaning that a dengue sample might produce a positive Zika test. They also trigger similar symptoms, including fever, headaches, and body pain. Samples often need to be sent to state labs to confirm the infection, which is expensive, time-consuming, and not realistic on a mass scale. That made it challenging to accurately track the recent Zika outbreak as it swept through South and Central America.
A 15-minute test
The new test exploits a quirk in how the viruses affect the body. Zika and the four strains of dengue each cause infected cells to release a slightly different version of a protein called NS1.
For the test, antibodies that can uniquely identify those specific Zika or dengue NS1 proteins are embedded onto a paper strip, along with gold nanoparticles. The end result is that if the virus is present in the sample, a red dot will appear on the strip.
The test works best when analyzing serum — a component of blood that can be easily separated out in health clinics — but the researchers said it should also work on blood samples.
“All you do is mix the serum with a solution and you dunk a paper strip into it,” said Kimberly Hamad-Schifferli, an engineer at the University of Massachusetts, Boston, and visiting scientist at the Massachusetts Institute of Technology, who helped lead the research. “You wait 15 minutes and you look for the appearance of a colored dot.”
The Zika test accurately identified infections in 81 percent of positive samples and incorrectly identified an infection in negative samples 14 percent of the time.
The test can also differentiate among the four strains of dengue. Getting infected with one strain, or serotype, doesn’t protect someone from contracting another strain later on, and those multiple infections increase the risk that the person will develop a much more severe illness called dengue hemorrhagic fever.
“Being able to distinguish the four serotypes is very important for epidemiology purposes and to know what viruses are circulating in an environment,” said Lee Gehrke, an engineer at MIT and one of the leaders of the research.
Currently, each paper strip is built to pick up on only one virus, so it would require five different versions to identify exactly what virus was causing an infection. But the researchers said they’re exploring how they could compile all five tests into one strip.
Nikos Vasilakis, a Zika expert at the University of Texas Medical Branch at Galveston who was not involved in developing the test, said the test’s cost and the simplicity could make it a widely used tool in the parts of the world where these viruses circulate. The cost per strip now is in the $5 range, but the researchers said they expect that to drop with scaled-up production.
“The test will be in a single dollar range, which is the biggest advantage in a resource-poor countries,” Vasilakis said. “The other advantage is that it’s very easy to use.”
The researchers traveled to places in Central and South America and India to validate their test on samples from patients with confirmed infections. The paper’s long list of authors includes many scientists from those countries who helped the researchers secure samples for testing.
The number of new Zika cases has dwindled since the major outbreak in the Americas in 2015 and 2016, but experts anticipate future outbreaks. The researchers also said they plan to apply the platform they used to build the Zika and dengue test to come up with diagnostic tests for other viruses.