gut bacteria
The bacterium, Enterococcus faecalis, which lives in the human gut, is just one of the many microorganisms that line the human alimentary canal. Centers for Disease Control and Prevention (CDC)

A team of researchers led by scientists from the San Diego State University discovered a previously unknown but surprisingly common virus living in the human gut, the BBC reported Saturday.

In a study published in the journal Nature Communications, the team of scientists stated that they stumbled upon the CrAssphage virus while going through the results from previous studies on gut-inhabiting viruses. When they attempted to check the discovery against a database of all known viruses, they came up empty-handed.

However, when they screened for the virus in fecal samples obtained from the database of the National Institute of Health's Human Microbiome Project, they found it in more than half of the samples.

The Human Microbiome Project is a five-year project launched by NIH in 2008 to understand the association between microorganisms living inside the human body and various diseases.

Robert Edwards, the lead author of the study, told BBC News that while finding a new virus in itself wasn’t that unusual, the fact that a virus this common -- more than half the world’s population is now suspected of harboring it -- had “flown under the radar for so long is very strange.”

Since the virus is so widespread across the human population, Edwards said that it was at least “as old as humans are.”

The virus has now been classified as a bacteriophage -- one that infects bacteria living in the human gut. According to the scientists, CrAssphage infects one of the most common classes of gut bacteria -- the Bacteroidetes -- which live near the end of the intestinal tract.

Bacteriophages are “critical components of our gut ecosystems, helping control the growth of bacterial populations and allowing a diversity of species,” Edwards stated.

As present though, scientists have not been to figure out the exact role played by the virus in the human gut ecosystem and the affect it has on the gut bacteria.