Researchers have created what they say is a “one-stop shop” for diagnosing infections – a test that can determine an individual’s complete viral history just by scanning a single drop of blood.
The test, called VirScan, was created by Stephen Elledge and colleagues from the Howard Hughes Medical Institute (HHMI).
“We’ve developed a screening methodology to basically look back in time in people’s [blood] sera and see what viruses they have experienced,” explains Elledge. “Instead of testing for one individual virus at a time, which is labor intensive, we can assay all of these at once. It’s one-stop shopping.”
The team explains how VirScan works in a new study published in the journal Science, in which they also reveal how the test performed when tested on the blood samples of more than 500 participants infected with certain viruses.
Elledge and colleagues synthesized over 93,000 short sections of DNA to create the test, each section encoding various pieces of viral proteins, called peptides.
Next, the team introduced the DNA sections to bacteriophages – viruses that invade bacterial cells and infect them. Each bacteriophage molded with a peptide, with the peptide displayed on the bacteriophage’s surface.
Together, the bacteriophages show all protein sequences present in the more than 1,000 strains of human viruses currently known.
Explaining how VirScan identifies viruses in blood samples, the researchers note that antiviral antibodies present in the blood recognize unique characteristics known as epitopes, which are found in peptides on the surface of each bacteriophage. When the bacteriophages are combined with a blood sample, antibodies in the blood identify and bind to these epitopes.
The researchers then collect these antibodies and dispose of everything except the bacteriophages they are attached to.
By conducting DNA sequencing on these bacteriophages, the team is able to identify the peptides that the antibodies clung to, revealing which viruses an individual’s immune system has come across previously, whether through infection or vaccination.
It is likely to take around 2-3 days for VirScan to analyze 100 blood samples, according to Elledge, though he is confident that this processing time can be increased the more the test is developed. It would cost around $25 to analyze one blood sample.
The researchers tested VirScan on the blood samples of 569 people from the US, South Africa, Thailand and Peru, all of whom were known to have been infected with certain viruses, including human immunodeficiency virus (HIV) and hepatitis C.
Overall, VirScan analyzed around 100 million possible interactions between antibodies and epitopes from the blood samples, with the test producing very accurate results, according to the team. Elledge says:
“We were in the sensitivity range of 95-100% for [HIV and hepatitis C], and the specificity was good – we didn’t falsely identify people who were negative. That gave us confidence that we could detect other viruses, and when we did see them we would know they were real.”
The team found that each individual included in the study had an average of 10 different viruses, with people in South Africa, Peru and Thailand possessing antibodies against more viruses than those in the US.
In addition, they found that adults possessed antibodies against more viruses than children, and individuals with HIV had antibodies to more viruses than those without HIV.
Perhaps the most surprising finding, however, was that antibody responses against certain viruses were found to be similar in each individual; different people’s antibodies recognized exactly the same amino acids present in the peptides of specific viruses.
The researchers are confident that VirScan could be an effective alternative to existing viral testing methods, which test for specific viruses one by one.
As the test can determine an individual’s viral history, the team believes it offers the potential to uncover factors affecting health that may have been overlooked. The test also provides the opportunity to assess and compare viral infections in large populations, and it may even have implications for vaccine design.
Their study, the researchers say, has helped them improve the accuracy of VirScan, and they hope it will improve further with more research.
The approach used to create VirScan could also be applied to identify other antibodies, the team notes, such as those involved in autoimmune diseases, in which the immune system attacks the body’s healthy tissues.