Researchers have developed a cheap and rapid test that reveals a person’s full history of viral infections from a single drop of blood.
The test allows doctors to read out a list of the viruses that have infected, or continue to infect, patients even when they have not caused any obvious symptoms.
The technology means that GPs could screen patients for all of the viruses capable of infecting people. It could transform the detection of serious infections such as hepatitis C and HIV, which people can carry for years without knowing.
“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,” said Stephen Elledge, who led the project at Brigham and Women’s Hospital in Boston.
“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 said.
The (£16) test draws on advances in synthetic biology and rapid gene sequencing to analyse more than 1000 strains of human viruses in one pass. Until now, most tests have looked for only a single virus at a time. Elledge estimates that the latest test, called VirScan, can process 100 samples in two to three days.
The test exploits the fact that the immune system makes antibodies to fight viruses whenever the body becomes infected. These antibodies can live on in the bloodstream for years and even decades.
To develop the test, Elledge engineered batches of harmless viruses to carry bits of proteins from human viruses on their surfaces. In total, they carried proteins from more than 1000 strains of the 206 kinds of viruses known to infect people. Antibodies use these protein fragments to recognise invading viruses and launch their attacks.
When a droplet of blood from a patient is mixed with the modified viruses, any antibodies they have latch on to human virus proteins they recognise as invaders. The scientists then pull out the antibodies and identify the human viruses from the protein fragments they have stuck to.
“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,” said Elledge. The test picks up the antibodies a person produces from vaccinations, but these can be discarded from the test results. Details are reported in the journal Science.
In a demonstration of the technology, the team analysed blood from 569 people in the US, South Africa, Thailand and Peru. The test found that, on average, people had been infected with 10 species of viruses, though at least two people in the trial had histories of 84 infections from different kinds of viruses.
The most common infections were herpes viruses, which cause cold sores, enteroviruses that upset stomaches, influenza, and rhinoviruses that trigger common colds. Those in the US had experienced fewer infections than those in the other countries, and as expected, older people had richer viral histories than youngsters.
The test could bring about major benefits for organ transplant patients. One problem that can follow transplant surgery is the unexpected reawakening of viruses that have lurked inactive in the patient or donor for years. These viruses can return in force when the patient’s immune system is suppressed with drugs to prevent them rejecting the organ. Standard tests often fail to pick up latent viruses before surgery, but the VirScan procedure could reveal their presence and alert doctors and patients to the danger.
“This could be very valuable,” said Iwijn De Vlaminck, a biomedical engineer at Cornell University in New York, who was not involved in the study. “What this allows you to do is look into the past and measure a person’s exposure to previous infections. That has important advantages, because you can detect these infections that go to latency. You could screen blood from patients and organ donors in this very broad manner and predict potential future issues with viral reactivation.”
Scientists believe the test will also cast light on how certain viral infections can predispose people to seemingly unrelated diseases later in life. Some infections can cause permanent damage to body tissues, or alter the immune system, in ways that leave people more at risk of medical problems when they are older. For example, infection with Epstein-Barr virus can raise the risk of cancer. But how other viruses affect long term health is far murkier. “That kind of analysis is something this really makes possible,” said Elledge.
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