Thursday, June 4, 2015

Blood test for every virus at once

Cheap blood test reveals every virus you've ever been exposed to

19:00 04 June 2015 by Jessica Hamzelou

You'll probably remember the last time you had the flu, but what about
that time you had measles – or was it chicken pox? Your blood knows:
it keeps a record of every virus you've ever been infected with. A
tiny drop of the stuff can now be tested to reveal a person's viral

The test, called VirScan, reveals that adults around the world tend to
have been infected by an average of 10 viruses over their lifetime. It
could also be used to identify links between viral infections and
mysterious diseases like chronic fatigue syndrome.

When a virus infects us, our immune cells respond by producing
antibodies that neutralise it when they bind to specific proteins on
its surface. These antibodies continue to be made long after the virus
has been cleared from our body, ready to mount a quicker response
should it return.

This means that their presence can act as a viral footprint – a clue
that the viruses they target were once in the bloodstream. To test
whether someone has been infected with a virus, expose a sample of
their blood to a viral protein. If antibodies target it then the virus
has infected the person in the past.

Stephen Elledge at Harvard University and his colleagues have pushed
this idea further and developed a way to test a blood sample for every
single family of human virus in one go.

Gotta catch 'em all

Elledge says that all he needs to carry out the test is a tiny amount
of a person's blood – less than a drop. It costs just $25, and could
help doctors identify hidden infections. "A lot of people have
hepatitis C, for example, without realising," says Elledge. You could
imagine routinely screening people in this way, he says.

To develop VirScan, Elledge and his colleagues used an international
database to look up all viruses known to infect humans – around 1000
strains from 206 viral species. Using this information, they recreated
the DNA in each virus that's responsible for making its proteins, and
put the DNA segments into individual bacteriophages – viruses that
infect bacteria. Each bacteriophage then manufactures a particular
viral protein on its surface.

When someone's blood is mixed with the bacteriophage brew, any
circulating antibodies latch on to the associated proteins on the
bacteriophages. Sequencing these bacteriophages then reveals the
person's viral history.

David Matthews at Bristol University in the UK thinks the best use of
VirScan might lie outside of diagnostics, considering we already have
quick and easy tests for individual viruses. "Usually when you've got
a set of symptoms, doctors have a pretty good idea of what you've
got," he says.

Moreover, the immune system takes a while to make antibodies, so you
might not find a strong antibody response in the early stages of an
infection. The test would also not be able to distinguish between
antibodies made as a result of an infection and those triggered by a

Disease detective

Instead, the technique might be useful in outbreaks of new viruses.
Understanding how our immune system responds to other viral fragments
might reveal clues as to which family the new virus belongs to, says
Pamela Vallely at the University of Manchester, UK. "If we'd have had
this test during the HIV outbreak in the 1980s, it would have given us
a clue for where to be looking to find out more about the virus," she
says. "It's a really exciting technique."

As well as playing an investigative role in outbreaks, VirScan could
also offer a way to investigate whether viruses are involved in
disorders that aren't well understood. For example, Elledge's team
will be collaborating with another group to test people with chronic
fatigue syndrome, to see if they might have been infected with any of
the same viruses.

"Multiple sclerosis is usually wheeled out as being linked to a
virus," adds Vallely. "You could check."

Down on the farm

The team used the test to screen blood samples from 569 people from
four countries – the US, South Africa, Thailand and Peru. As you might
expect, adults appeared to have encountered more viruses than
children. Each person had been infected with an average of 10 viruses
over their lifetime.

Matthews thinks it would be worth extending the screen to animal
populations. He envisages screening wild populations of animals
thought to be linked to emerging diseases. "You could test the wild
bat population to get a good idea of what viruses are out there," he

At the same time, farm animals could be comprehensively screened.
Farmers that are able to identify viruses affecting the health or
yields of their herds might be able to halt the spread of those
viruses, says Matthews.

"It is a fantastic piece of work and will be very, very useful," he says.

Journal reference: Science, DOI: 10.1126/science.aaa0698

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