Thousands of years ago, travelers and traders carried goods across the vast distances between Europe, the Middle East and Asia along routes that collectively become known as the Silk Road. Named after the silks that were exported from China, the routes helped spread news, art and culture through a large part of the world. Now, a new study focused on a 2,000-year-old Silk Road latrine shows that the routes also helped spread something else – disease.

A team of researchers from the University of Cambridge and China's Academy of Social Sciences and Gansu Institute for Cultural Relics and Archaeology investigated latrines at the Xuanquanzhi relay station, an archeological site in northwestern China that once served as a rest stop of sorts along the Silk Road. It was built in 111 BC and used until 109 AD (the Silk Road itself is generally acknowledged to have existed from about 130 BCE to about the mid 1400s).

There they found hygeine sticks that had bits of cloth stuck to them that were used by people to clean up after using the latrine. Based on their function, the sticks also held bits of ancient feces. By analyzing the feces, the researchers found the eggs from four species of parasitic worms: roundworm, whipworm, tapeworm and Chinese liver fluke.

"This may seem surprising," writes Cambridge researcher and study co-author Piers Mitchell on academic site The Conversation, "but the eggs of many species of intestinal worms are very tough and may survive thousands of years in the ground."

Of the parasites, one stood out – the liver fluke.

That's because the location of the archeological site is situated in a dry area of the country. In fact, it's not too far away from China's Takla Makan Desert. The thing is, Chinese liver flukes are only native to wet marshy areas, so there's no way it could have been living in the area of the latrine. In fact, Mitchell says, it must first pass through a water snail and then a freshwater fish which much be eaten raw before infecting humans. Because no such animals exist near the latrine, the parasite must have been brought there by a traveler.

So just how far did that traveler bring his unfortunate cargo?

According to the researchers, based on current conditions, the only area it could have come from is about 1,500 km (923 mi) away. And today, the area where most of the infections are found is even farther, at 2,000 km (1,243 mi) away.

"When I first saw the Chinese liver fluke egg down the microscope I knew that we had made a momentous discovery," said Hui-Yuan Yeh, one of the study's authors. "Our study is the first to use archaeological evidence from a site on the Silk Road to demonstrate that travellers were taking infectious diseases with them over these huge distances."

While it's been previously suggested that major diseases like the bubonic plague, leprosy and anthrax spread along the Silk Road, the researchers say that there's never been hard-and-fast proof, because the organisms could have taken a different route between China and Europe.

"Our finding suggests that we now know for sure that the Silk Road was responsible for spreading infectious diseases in ancient times," says Mitchell. "This makes more likely previous proposals that bubonic plague, leprosy and anthrax could also have been spread along it."

The research has been published in the Journal of Archaeological Science: Reports.

Source: University of Cambridge, The Conversation