How This New Blood Test Reveals Your History of Viral Infections

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Imagine a test that can reveal nearly every virus you've ever had with a single drop of blood.

Scientists at Harvard Medical School and Brigham and Women’s Hospital say they can do just that with a cheap, new method called "VirScan."

Dozens of news outlets covered the announcement late last week. On reviewing some of the reader comments, it seems that some of you were surprised as I am that a test like this hasn't been on the market for years.

Here's our explainer of everything you need to know about this breakthrough with some added context:

How does this test work?

The test looks for the antibodies that your body has used to fight previous viral infections -- thus, the researchers refer to it as a viral history test. A drop of blood carries plenty of information about previous viruses you've encountered.


The test can detect past exposure to more than 1,000 strains of viruses from 206 species. This encompasses most of the human “virome,” meaning all the viruses known to infect people. The Washington Post has a great infographic to explain the science in more detail.

Note, the test isn't perfect: It can miss some small infections and it may conflate two related viruses. But many medical experts say this is an important technological feat, which will change the practice of medicine. As Dr. David Agus put it on CBS This Morning:

What I really believe is, every year you go to a doctor, we're gonna take a drop of that blood and we're gonna get your viral history for that year.

What were the results from the first set of studies?

The researchers screened 569 human donors from across four continents: United States, South Africa, Thailand and Peru. They reported to Science that the VirScan method at revealing viruses is as effective as single tests, which screen for one virus at a time.

On average, the test revealed ten viral species per donor. As you might imagine, these tended to be the most common infections, like colds and flus. Two individuals, however, had encountered 84 species of viruses.

Why bother to test for previous viral infections?

A viral infection can alter your immunity in myriad ways, including many that we do not yet understand.

From the introduction to the research paper in Science:

The collection of viruses found to infect humans can have profound effects on human health...This interplay between virome and host immunity has been implicated in the pathogenesis of complex diseases such as type 1 diabetes, inflammatory bowel disease, and asthma.

It's not yet clear whether the test will prove useful for diagnostic purposes. But we do know that doctors are limited today as they can only screen for one pathogen at a time.

The report in Science hypothesizes that in the future, your doctor will be able to detect a potential link between past viral infections and current diseases.

How much does it cost?

VirScan analysis currently can be performed for about $25 per blood sample, but the first labs that carry the test may charge much more. It's unclear when the test will hit the market -- the researchers do not yet know when they will commercialize the research.

What will be the first applications for the test?

The research may support early detection of some diseases, and help us understand the triggers for some autoimmune diseases and cancers.

Stephen J. Elledge, the senior author of the report and a professor of genetics at Harvard Medical School and Brigham and Women’s Hospital, told the New York Times that researchers will come up with applications that "we haven't even dreamed of."

Were there any early surprises?

Dr. Ellege told the New York Times that he was surprised about one finding in particular. For patients with H.I.V, he expected that the immune response to other viruses would be diminished. “Instead, they have exaggerated responses to almost every virus,” he told The New York Times -- and the researchers do not yet have an explanation.

What's next?

Believe it or not, we still do not have a widely-available test that uses a drop of blood to determine whether a person is experiencing a viral, bacteria or fungal infection - although researchers have made some important strides in recent years.

The researchers behind VirScan say they hope to expand the test to include new viruses, as they're discovered, as well as other human pathogens, like bacteria, fungi, and protozoa.

What are the implications of that? For starters, doctors will be less likely to prescribe antibiotics that don't work on viral infections. The overprescription of antibiotics is a public health concern, as it can contribute to the development of antibiotic-resistant bacteria. More on that here. 

VirScan's test may also prove valuable to the scientific community through the data it collects. Its method may result in a "big data" set for viral exposures, which researchers could use to shed light on many illnesses. Dr. Ellege told the New York Times he hopes to solve at least one medical mystery: Why do some people respond well to chemotherapy and not others?