Researchers from Washington University in St. Louis have developed a new test that detects Zika virus in the blood.
Current tests for Zika require a blood sample to be refrigerated and shipped to a medical center or laboratory. This delays diagnosis and treatment that may save the person’s life. This new proof-of-concept technology provides test results in minutes. The materials required for the test don’t involve refrigeration and might be usable in testing for other emerging infectious diseases.
The researchers tested blood samples taken from people infected with the Zika virus and then compared samples to blood from five people who did not have the virus. Blood from the Zika patients tested positive and the blood from Zika-negative patients tested negative. Significantly, the assay had no false-positive results.
One of the main reasons that this test is needed it that people infected with Zika may not know that they are infected. Symptoms include fever, joint pain, muscle pain and rash, but many people don’t feel sick or show symptoms after being bitten by an infected mosquito. Testing for Zika is very important for pregnant women because Zika can cause congenital Zika syndrome. This syndrome contributes to neurologic problems in a fetus or newborn 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."
The new strategy required inexpensive, easy-to-use and easy-to-transport tests. The test uses gold nanorods mounted on paper to detect the Zika infection within a few minutes, as opposed to the days the previous test may take.
"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."
This test relies on a protein made by the Zika virus that causes an immune response in infected patients. This protein is attached to the gold nanorods. The paper on which they are mounted is then covered with tiny, protective nanocrystals. The nanocrystals allow diagnostic nanorods to be shipped and stored without refrigeration before use.
To use the test, the technician rinses the paper with slightly acidic water, removing the protective crystals to expose the protein mounted on the nanorods. Then a drop of the patient’s blood is applied. If the patient has been exposed to Zika, the blood will contain immunoglobulins which react to 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 color change that can be detected with a hand-held spectrophotometer. With this test, results will be clear before the patient leaves the clinic, allowing immediate counseling and access to treatment."
The color change cannot be seen by the naked eye, but scientists are taking the next step towards that. They are also working on developing ways to use saliva rather than blood. The test is not yet available for general use in the field.
The test uses gold, but the nanorods are very small. The cost of the nanorods is 10 to 15 cents per test.
A paper on this research was published in Advanced Biosystems.