Although royal, Richard could not escape a common parasite of the late Middle Ages, they said, given the poor hygiene of the period.
"This is the first time anyone has studied a king [or] noble in Britain to look for ancient intestinal parasites," Piers Mitchell at the University of Cambridge told NBC News in an email.
"[T]hey may have been spread to Richard by cooks who did not wash their hands after using the toilet, or by the use of human feces from towns to fertilize fields nearby," he explained.
Intestinal parasites have plagued humans throughout history and remain a global problem today, experts say.
Although "uncommon" in the United States, roundworm afflicts up to 1.2 billion people worldwide, the Center for Disease Control and Prevention says.
"Despite Richard's noble background, it appears that his lifestyle did not completely protect him from intestinal parasite infection, which would have been very common at the time," says Jo Appleby, a bioarcheologist at the University of Leicester who was part of the team that unearthed Richard's remains in 2012 from a Leicester parking lot.