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The previously unknown virus affects a common type of gut bacteria called bacteroidetesSkinnychef.com

Scientists have discovered a previously unknown virus that exists in half of the population of the planet and could play a major role in obesity and diabetes.

A new study led by biologists at San Diego State University unearthed a newly-described virus called crAssphage, which infects one of the most common types of gut bacteria, Bacteroidetes.

This phylum of bacteria is thought to be connected with obesity, diabetes and other gut-related diseases, and as the virus is so widespread, researchers suggest it is likely to be as old as humankind.

"We've basically found it in every population we've looked at," bioinformatics professor Robert Edwards explained. "As far as we can tell, it's as old as humans are."

The researchers stumbled upon the discovery by accident, when they were using results from previous studies on gut-inhabiting viruses to screen for new viruses.

In the DNA fecal samples from 12 different individuals, they noticed a particular cluster of viral DNA, about 97,000 base pairs long, that the samples all had in common.

When the researchers screened the virus across the database of the National Institute of Health's Human Microbiome Project (HMP) and Argonne National Laboratory's MG-RAST database, they found it in abundance in samples derived from human feces.

To prove that the viral DNA they discovered in their computer data actually exists in nature, virologist John Mokili used a technique known as DNA amplification to locate the virus in the original samples used to build NIH's database.

"So we have a biological proof that the virus they found with the computer actually exists in the samples," Mokili said, as reported by Science 2.0.

This was a new virus that about half the sampled people had in their bodies that nobody knew about.

Edwards added: "It's very unusual to find a virus that so many people have in common. The fact that it's flown under the radar for so long is very strange."

Some of the proteins in crAssphage's DNA are similar to those found in other well-described viruses, which allowed Edwards' team to determine that their novel virus is one known as a bacteriophage, which infects and replicates inside bacteria.

Using bioinformatic techniques, they predicted that this particular bacteriophage proliferates by infecting a common phylum of gut bacteria known as Bacteriodetes, which live towards the end of the intestinal tract.

The virus might also be used to prevent or mitigate other diseases affected by the gut such as diabetes and gastroenterological maladies, according to Science Daily.

Once these processes are better understood, Edwards envisions one day the possibility of personalised medicine based on this virus.

"This could be a key to personalised phage medicine," he said. "In individuals, we could isolate your particular strain of the virus, manipulate it to target harmful bacteria, then give it back to you."

The research was published in Nature Communications.