An international research team led from Australia and China has discovered nearly 1,500 new viruses. The scientists looked for evidence of virus infection in a group of animals called invertebrates, which includes insects and spiders.

Not only does the study expand the catalogue of known viruses, it also indicates they have existed for billions of years.

The findings were published in the journal Nature.

Few would argue that all living species on Earth are susceptible to viruses – these microscopic parasites are ubiquitous.

But virologists have long suspected that our current view of the diversity of viruses is blinkered – all too often constrained to those causing disease in humans, animals and plants, or to those that we can grow in the laboratory.

A trip to a tropical rainforest or the African savannah gives a snapshot into the incredible diversity of visible life on Earth, but understanding the potentially mind-boggling myriad of minuscule viruses has not been so easy.

Capturing new viruses is not like netting a new species of butterfly – viruses are invisible.

Undeterred by this practical problem an international team was keen to survey invertebrates for new viral species.

Invertebrates are spineless creatures and the group includes many familiar animals, such as insects, spiders, worms and snails. They represent the vast majority of animal species in the world today.

Scientists wanting to work out the totality of viral “life” – although many virologists would argue that viruses are not truly alive – are starting to adopt techniques that reveal their genetic calling cards, revealed in the things they infect.

Just like powerful new telescopes are peering deeper into space, revealing a wealth of hitherto unknown stars, next-generation sequencing techniques are providing new insight into the magnitude of the invisible world of viruses; a world we call the virosphere.

We are familiar with DNA, the “stuff of life” that makes up the blueprint of our genomes. But many viruses use a different chemical to construct their genomes – a substance known as RNA.

Just like DNA, this consists of strings of individual building blocks, or bases; each designated by a different letter: A, C, G and U.

Next generation sequencing allows researchers to quickly determine the sequence of these letters. And if you work out the order of the letters on any chain of RNA, you can determine if it belongs to a virus and whether or not the virus is new.

“If we have learned anything from these types of true discovery projects is that when we start looking into places we haven’t looked at before, we find an incredible richness that goes beyond what was suspected.

“It also makes a strong case for expanding virus surveillance to invertebrates in our quest to better understand (and predict) emerging viruses,” she said.

‘Looking back’

The researchers hope that next-generation sequencing can pave the way for virus discovery in a variety of other species. And it does not stop there.

Prof Delwart thinks that further analyses of existing next-generation datasets may yield additional virus species unlike any that we have seen before.

If future studies reveal anywhere near this number of new viruses, then we’ve only just scratched the surface. It seems that the virosphere is set to explode.