Researchers have devised a method of identifying a person's complete viral history using a $25 blood test and a single drop of blood.

VirScan was introduced in this month's Science and it is a simple blood test that can identify every virus an individual has been exposed to, which could radically change the way doctors diagnose their patients.

"Normally, when a doctor wants to know if someone's been infected with a virus, they have to guess what the virus is, and then look specifically for that virus," coauthor of the project and physician at Brigham Women's Hospital, Boston, Stephen Elledge says. "This could lead to a diagnostic where people go annually to their doctor and get their viral history recorded. It could certainly discover viral infections that are serious and that a patient didn't know they had," he added.

Whenever a person comes in contact with a virus, the body produces an immunological response, creating antibodies for that specific pathogen. VirScan identifies these antibodies and can thus provide a list of exposures, both past and present.

Elledge and colleagues engineered harmless viruses that carried bits of proteins on their surfaces; proteins that are targeted by antibodies within the immune system. Over 1,000 strains of the 206 viruses known to infect humans were used, and when the person's blood was tested, any antibodies they had that adhered to the viral proteins were isolated and identified.

Over 560 people from the U.S., South Africa, Thailand, and Peru were tested. VirScan showed that on average, people had been exposed to around 10 species of viruses at some point in life, the most common being herpes, enteroviruses, influenza, and the rhinoviruses that cause common colds. At least two people in the study showed a whopping 84 viral exposures.

"It's the first time we've been able to look in a completely unbiased manner at what viruses are infecting people, and we can do it for all known viruses."