What can parasite eggs preserved in medieval poop tell us about human history?

Most people don’t get excited about intestinal parasite eggs preserved in 500-year-old human feces. But Marissa Ledger isn’t like most people.

“A lot of my research is focused on actually studying ancient poo, or ancient fecal material, as I sometimes try to say to put it nicely,” she told As It Happens host Nil Kӧksal. 

Ledger is a biological anthropologist, working as post-doctoral fellow at McMaster University’s Ancient DNA Centre in Hamilton, Ont. So when archaeologists in Belgium started digging into the remnants of a medieval latrine in Bruges, they knew who to call.

Now, she and her Belgian colleagues have found thousands of parasitic eggs in the toilet of yore — including one that came all the way from Africa.

Their findings, published in the journal Parasitology, sheds light on the robust trade networks and day-to-day life of the medieval period, and helps scientists understand the spread of diseases, both then and now.

1 gram of fecal matter is all you need

The latrine was a part of a building known as the Spanish nation house in Bruges, a city heavily involved in international trade and home to people from all over the world. 

The house would have been home to Spanish traders who were active in the city mostly from the late 15th century onwards.

The latrine was first discovered during excavations in 1996, but its contents are only now being studied, due to modern technology. 

Ledger’s job was to examine samples of soil from the latrine which is, in fact, preserved fecal material. Within just one gram of the soil, she found thousands of parasitic eggs.

“That tells us …. there are a number of different people who used that washroom in that house who were infected with different parasites,” Ledger said.

“People living in the city were getting parasites within Bruges, and that was probably a normal occurrence…. But they were also getting parasites from farther abroad as well.”

The ‘cool’ thing about parasites

That, she says, is proven by the presence of Schistosoma mansoni, a water-borne parasitic flatworm that enters the body through the skin and takes up residence in the intestines, where it lays eggs.

This parasite is predominantly found in Africa where it originated, and more recently in South America, likely the result of the Atlantic slave trade.

“It’s very exciting to see this parasite somewhere where it shouldn’t be,” she said. “It tells us [Bruges] had a link to Africa at that time.”

That, she says, is the “cool” thing about parasites: they paint a picture of human migration unfolding throughout history.

But there’s nothing cool about schistosomiasis, the disease caused by the parasite which, according to the World Health Organization, can cause abdominal pain, diarrhea, kidney damage and in some rare cases, death.

Ledger says understanding the movement of parasites and diseases throughout history can help doctors treat and prevent them today.

“Understanding how humans have changed how those parasites have been spread around, and how we’ve impacted their predominance through time, gives us some idea [of how] we control them from a public health strategy,” she said.

Kirsten Bos, a physical anthropologist who studies ancient DNA and infectious disease and was not involved in the study, says the disease likely didn’t spread within Belgium once it arrived there 500 years ago.

That’s because Schistosoma mansoni needs two hosts to complete its life cycle: humans, where it undergoes sexual reproduction, and freshwater snails, which allow it to transmit through water.

“Someone in Bruges had the infection and shed the parasite. But without the snail, I don’t think this caused any public health issue,” Bos, of the Max Planck Institute for Evolutionary Anthropology in Germany, said. 

“But I guess the traveller might have had a rough trip.”

Archeology about more than clay pots

It’s not clear how exactly the parasite ended up on Belgium. It could have been a Spanish trader bringing gold dust, ivory and spices from Africa. It also could have been from someone connected to the Atlantic slave trade.

Or it could have originated with an African visitor. The study notes the first documentation of an African person in Bruges dates back to 1440.

Co-author Maxime Poulain, an archaeologist at Ghent University in Belgium, says the findings are an example of the complexity of life in a medieval city.

“It not only gives a new insight into the daily lives of people in medieval Bruges, but also shows how the city — as an international hub for people, goods and ideas — inevitably provided for the spread of diseases,” he said in a university press release.

It’s an area of study that’s ripe for more exploration, added co-author Koen Deforce, a Ghent archaeobotanist.

“‘Whereas the focus used to be on studying objects made of clay and metal, we are now increasingly looking at organic material to learn more about the diet, health, hygiene and mobility of past populations,” he said.

In fact, this isn’t the only study to examine the remnants of ancient toilets. Just last year, researchers found traces of dysentery-causing parasites in the cesspits below 2,500-year-old stone toilets excavated in Jerusalem.

One of the authors of that study, University of Cambridge biological anthropologist Piers Mitchell, lauded this latest finding in Belgium. Ledger is his former PhD student. 

“The discovery shows that those involved in long distance trade between Africa and the Low Countries during the 15th century took their parasites with them on their journeys,” he said in an email.