Researchers now have the ability to test for more than 1,000 strains of virus in a single drop of blood, even if the patient is no longer infected.

The new screening method, dubbed VirScan, can reveal a person's viral history, Bringham and Women's Hospital reported. Current blood tests, called ELISA assays, can only detect one virus at a time and have not been developed to recognize all known viruses. The technique revealed an average of 10 viral species per person it was tested on. The findings provide insight into the connection between a person's immunity and their virome, and could lead to breakthroughs in the field of immunology.

"VirScan is a little like looking back in time: using this method, we can take a tiny drop of blood and determine what viruses a person has been infected with over the course of many years," said corresponding author Stephen Elledge, a principal investigator in the Division of Genetics at BWH and Gregor Mendel Professor of Genetics and of Medicine at Harvard Medical School. "What makes this so unique is the scale: right now, a physician needs to guess what virus might be at play and individually test for it. With VirScan, we can look for virtually all viruses, even rare ones, with a single test."

To test VirScan, the researchers applied it to blood samples from almost 600 people from Peru, the United States, South Africa and Thailand. The findings showed a small number of peptides (small protein fragments from viruses) were recognized by the majority of participants' immune systems, suggesting most immune systems hit the same protein in a virus; this could provide key insights into immunity. The new method could also help identify links between previous viral exposure and disease development later in life.

"A viral infection can leave behind an indelible footprint on the immune system," Elledge said. "Having a simple, reproducible method like VirScan may help us generate new hypotheses and understand the interplay between the virome and the host's immune system, with implications for a variety of diseases."

The findings will be published in an upcoming edition of the journal Science.