Trillions of Viruses Live in Your Body. A.I. Is Trying to Find Them.

The Human Virome Program will analyze samples from thousands of volunteers in an effort to understand how viruses affect health.

The viruses we know best are the ones that make us sick — the influenza viruses that send us to bed and the smallpox viruses that may send us to the grave.

But healthy people are rife with viruses that don’t make us ill. Scientists estimate that tens of trillions of viruses live inside of us, though they’ve identified just a fraction of them. A vast majority are benign, and some may even be beneficial. We don’t know for sure, because most of the so-called human virome remains a mystery.

This year, five universities are teaming up for an unprecedented hunt to identify these viruses. They will gather saliva, stool, blood, milk and other samples from thousands of volunteers. The five-year effort, called the Human Virome Program and supported by $171 million in federal funding, will inspect the samples with artificial intelligence systems, hoping to learn about how the human virome influences our health.

“I think it will swamp the data that we’ve had up until now,” said Frederic Bushman, a microbiologist at the University of Pennsylvania and one of the program’s leaders.

The first hints of the human virome emerged over a century ago. Analyzing stool samples, scientists discovered viruses known as phages that could infect bacteria inside the gut. Phages also turned up in the mouth, lungs and skin.

Scientists later found viruses that infected our own cells without causing any major symptoms. A vast majority of the world’s population gets infected with cytomegaloviruses, for example, which can colonize just about every organ.