Zika virus diagnosed in minutes with proof-of-concept tool

Testing for Zika currently requires a blood sample be refrigerated and shipped to a medical centre or laboratory, which delays diagnosis and possible treatment.

Although the new proof-of-concept technology has yet to be produced for use in medical situations, the test's results can be determined in minutes. The materials required for the test do not require refrigeration and may be applicable in testing for other emerging diseases.

Findings from the small study - from Washington University in St Louis School of Medicine and the School of Engineering & Applied Science - are available online in Advanced Biosystems.

The researchers are said to have tested blood samples taken from four people infected with Zika virus and compared it to blood from five people without it. Blood from Zika-infected patients tested positive, while blood from Zika-negative controls did not. The assay produced no false-positive results.

Among the reasons such a test is needed, according to the researchers, is that many people infected with Zika don't know they're infected. Although symptoms can include fever, joint pain, muscle pain and rash, many people don't feel ill after being bitten by an infected mosquito. Testing is particularly important for pregnant women because Zika infection can cause congenital Zika syndrome, which contributes to several neurologic problems in the foetus or new-born infant.

"Zika infection is often either asymptomatic or mildly symptomatic," said Evan D Kharasch, MD, PhD, one of the study's three senior investigators. "The most effective way to diagnose the disease is not to wait for people to develop symptoms but to do population screening."

That strategy requires inexpensive, easy-to-use and easy-to-transport tests. Kharasch collaborated with Srikanth Singamaneni, PhD, an associate professor of mechanical engineering & materials science, and Jeremiah J Morrissey, PhD, a research professor of anaesthesiology, to create the test, which uses gold nanorods mounted on paper to detect Zika infection.

"If an assay requires electricity and refrigeration, it defeats the purpose of developing something to use in a resource-limited setting, especially in tropical areas of the world," said Singamaneni. "We wanted to make the test immune from variations in temperature and humidity."

The test relies on a protein made by Zika virus that causes an immune response in infected individuals. The protein is attached to gold nanorods mounted on a piece of paper. The paper then is completely covered with protective nanocrystals. The nanocrystals allow the diagnostic nanorods to be shipped and stored without refrigeration prior to use.

To use the test, a technician rinses the paper with slightly acidic water, removing the protective crystals and exposing the protein mounted on the nanorods. A drop of the patient's blood is then applied. If the patient has come into contact with the virus, the blood will contain immunoglobulins that react with the protein.

"We're taking advantage of the fact that patients mount an immune attack against this viral protein," said Morrissey. "The immunoglobulins persist in the blood for a few months, and when they come into contact with the gold nanorods, the nanorods undergo a slight colour change that can be detected with a hand-held spectrophotometer.

The colour change cannot be seen with the naked eye, but the scientists are working to change that. They're also working on developing ways to use saliva rather than blood.