A blood test is shown.
A new blood test can determine the viruses that a person has been exposed to over a lifetime. (For Spectrum Health Beat)

A single drop of blood may reveal a range of viruses a person has contracted recently, or possibly years ago, a new study suggests.

Writing in the June 5 issue of Science, researchers describe a new technology that can test for more than 1,000 viral strains at the same time—using one drop of blood.

Experts said the achievement could represent an advance over existing tests, which look for just one virus at a time. But for now, they see the one-stop, $25 test as useful for research purposes, rather than real-world diagnostics.

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Our Take

David Dobbie, MD, an infectious disease specialist with Spectrum Health Medical Group, agrees that while VirScan is an interesting technology and potentially valuable as a research tool, until a clinical correlation points to a definitive use for the test results, it’s not yet helpful in practice.

“As a doctor, whenever I order a test, I need to ask myself: How might the results change how I manage my patient’s condition? Impact my choice of therapy? Affect his or her prognosis or risk for further health issues?” he said. “With this test, these answers are all unknown.”

Dr. Dobbie doesn’t believe the test is available for use yet. And unless the above questions can be clearly answered, he said, physicians need to be cautious.

“The last thing we’d want to do is order it as part of a standard physical exam,” Dr. Dobbie said. “Knowing what a patient has been infected with, or exposed to, in the past does not translate into a meaningful clinical action in the present.”

In other words, this particular knowledge is not yet power.

“It’s hard to say how far off any clinical application could be,” said Tomasz Kula, one of the researchers on the study and a graduate student at Harvard University in Boston.

More immediately, Kula said, the test—called VirScan—could aid research.

“One example would be studies that look for correlations between people’s viral exposures and their risk of developing various diseases,” Kula said.

The Epstein-Barr virus, one of the most common viruses in humans, has been linked to increased risks of certain cancers. But studying such virus-disease connections has been challenging, Kula said, partly because current tests look for one virus at a time.

With VirScan, he explained, it might be possible to test a large group of people with a given disease and another group without the condition. Researchers could then see whether certain viral exposures were more common in people with the disease.

The VirScan test works by detecting antibodies to viruses known to infect humans; antibodies are evidence of a past immune system response to a particular virus.

To test the technology, Kula and his colleagues used blood samples from almost 600 people from the United States, Peru, South Africa and Thailand—all of whom were known to carry certain viruses, including HIV and hepatitis C.

Overall, the test accurately picked up more than 90 percent of those known infections, the researchers said. Plus, it rarely gave a positive result for someone who did not carry one of the viruses.

The test also detected antibodies against viruses that study participants were not known to harbor. On average, people had antibodies to 10 viruses, though a few had antibodies to at least 84.

Cold and flu viruses, along with various herpes viruses—including Epstein-Barr—were among the most common bugs detected.

According to Kula, it’s not clear how far back in time the test can dig. Over the years, antibodies to infection wane, he explained.

“This test gives a snapshot of the antibodies in your blood right now,” Kula said.

Plus, the typical adult has been exposed to far more than 10 viruses—the average in this study group, said Dr. Aaron Glatt, an infectious disease specialist who was not involved in the research.

“This is an interesting technology,” said Glatt, a spokesperson for the Infectious Diseases Society of America. “But I’m not sure how this would be used clinically.”

For one thing, Glatt explained, it takes time for the immune system to form antibodies to a particular virus. “It’s not clear how evidence of a past exposure would say anything about the acute symptoms a patient is having now,” he said.

“If you think a patient has HIV,” Glatt added, “you order an HIV test.”

He agreed, though, that the test might prove useful in the research setting.

The research team did come across one unexpected finding, Kula said. Overall, study participants had very similar immune responses to specific viruses: That is, each person’s antibodies were directed against the same amino acids within a given virus.

“That was surprising because the immune response is thought to be very personal,” Kula said.

Going forward, he added, that finding could have implications for understanding the immune response to infection.