Medical researchers identified a gut virus that is present in about half of the world's population and is believed to be linked to obesity.

The virus, dubbed crAssphage, was investigated by San Diego State University. The findings appear today in Nature Communications. The virus infects the most common type of gut bacteria, Bacteroidetes. This bacteria is associated with conditions such as diabetes and obesity.

The researchers made their findings by looking at previous studies on gut-inhabiting viruses in hopes of uncovering new ones. The DNA from fecal samples taken from 12 individuals held a cluster of viral DNA that was not recognized. They screened the virus across the database of the National Institute of Health's Human Microbiome Project (HMP) and found there was an abundance of the virus derived from human feces. The team used a technique called DNA amplification to prove crAssphage exists in nature.

"So we have a biological proof that the virus they found with the computer actually exists in the samples," SDSU virologist John Mokili said.

The virus proved to be present in about half of the people included in the study.

"It's not unusual to go looking for a novel virus and find one," said Robert A. Edwards, a bioinformatics professor at SDSU. "But it's very unusual to find one that so many people have in common. The fact that it's flown under the radar for so long is very strange."

Since the virus is so wide-spread it has most likely been around for quite some time; it could even be as old as the human population itself. It infects and replicates within bacteria living at the end of the intestinal tr  act. Researchers are unsure how the virus is transmitted, but since it is not present in infants it is most likely acquired sometime during childhood.

In the future the researchers hope to pinpoint the virus' role in obesity. The findings could also help mitigate diseases affected by the gut such as diabetes.

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