ROXANNE KHAMSI: Now turning the Parasite Wayback Machine to the medieval ages, you might think that the learned friars who lived in the town of Cambridge, scholars with access to innovations like latrines and places to wash their hands, might have lived healthier lives than the common folk.

But a recent study published in the International Journal of Paleopathology says that at least when it comes to intestinal parasites, the friars might have been worse off. Dr. Piers Mitchell is one of the authors of that paper. He runs the Cambridge Ancient Parasites Laboratory and is a senior research associate in the McDonald Institute for Archaeological Research at the University of Cambridge. Welcome, Piers.

PIERS MITCHELL: Nice to talk to you.

ROXANNE KHAMSI: So you’re talking to me from Cambridge in England. Let’s take the clock way back. Can you give me a picture of what the population was like in Cambridge in the medieval times and who was there?

PIERS MITCHELL: The time period that we’re looking at when we studied the skeletons for this project, we’re looking at about 12th, 13th, 14th, 15th century. And at that time, Cambridge had a population of between 2,000 and 5,000. And the population was gradually expanding over that time because as the university became more established, more people moved into the town, and it became a slightly bigger center.

ROXANNE KHAMSI: So what were the living conditions like back then?

PIERS MITCHELL: Well, it depends if you are poor or wealthy. So many people in Cambridge would have made part of their living or all their living from farming or from working as a trader or a merchant. Over time, more and more people joined the Cambridge population because of the academic role of the university.

But there were also a disproportionately large number of friaries and monasteries and nurseries. So there was a really big, long list of institutions. The friary that we studied was studium generale for the Augustinian Friars in England. So it was the main center for academic writing and scholarly manuscript reproduction, and so on. So Cambridge was quite a center for these religious orders.

ROXANNE KHAMSI: And I know we’re really used to sanitizing our hands these days, but I guess back then, it was a little bit less hygienic?

PIERS MITCHELL: Well, one of the key things is back then, they didn’t understand about infectious diseases and how diseases were spread. So they didn’t see the need for a lot of the things we perceive as good hygiene. They thought that those kind of illnesses were as a result of an imbalance of your four humors.

So they felt that if you had normal levels of phlegm, black bile, yellow bile, and blood, and that they weren’t corrupted by any disease process, then that kept you healthy. So they really didn’t understand that washing your hands might protect you from getting infectious diseases or intestinal problems.

ROXANNE KHAMSI: So you’re looking at parasites, and particularly the parasites that these people might have been infected with. Can you say a bit more about how you spotted those parasites?

PIERS MITCHELL: Well, the best way to try and work out how common parasites were are to look at skeletons in the ground and to take the soil from their pelvis, where the intestines would have been when they had these parasites. And then if you look at that soil down the microscope, you can see the microscopic things that are inside there. And while intestinal parasitic worms may be 5, 10, 30 centimeters in length and sometimes many feet in length, the eggs that they produce are tiny. So they may be fractions of 1,000th of a millimeter. So the only way to see those is using microscopy.

ROXANNE KHAMSI: And those are the ones that lasted in the archaeological record?

PIERS MITCHELL: That’s right. So the adult worms would die and decompose when their host dies and decomposes in the ground when they’re buried. But the parasite eggs are much tougher. And so we can find them hundreds of years later.

ROXANNE KHAMSI: Yum. [LAUGHS] So you’re sampling the dirt from around the remains in the graveyard, specifically around the pelvis of the skeletons. Can you tell us a little bit about what the findings revealed after you did all that analysis?

PIERS MITCHELL: Sure, so we wanted to not just study one population, but to do a comparison of different populations who lived different lifestyles. So we looked at the burials from a normal parish cemetery, called All Saints by the Castle, and then we compared them with the burials of friars inside the Augustinian friary.

And what’s special about this particular burial ground is that the friars were actually buried with their habits and their special belts on, so you can tell which ones are friars and which ones might be members of town who are buried in the friary burial grounds because you could do that if you paid extra by the fact that they still had their belts on. So we knew we were definitely dealing with the friars’ skeletons themselves.

And by comparing those two, we can see is there any difference in parasite infection that might reflect the different lifestyles that the poor peasants in town versus the friars would have actually sustained. We expected to find that the friars with their nice latrine [INAUDIBLE] and handwashing and rule of their order, which stressed the nature of hygiene and cleanliness, we expected them to have lower levels of parasite infection than we did in the general public, who, many of them were very poor. They may not have even had a cesspit toilet themselves.

And what we actually found was that compared with the poor members of the public, about 32% had intestinal worm infections. In the Augustinian friars, it was 58%, so that’s nearly twice the percentage that had these intestinal worms.

ROXANNE KHAMSI: How surprised were you when you found out this paradoxical result?

PIERS MITCHELL: Well, we thought, crikey, this is not what we were expecting. So now we had to take a step back and think, what is different about these two groups and the way they lived their lives, and what is special about the kind of parasites that were present? And the kind of parasites that were present were roundworm and whit worm. And these are spread by poor sanitation. So we didn’t find parasites that are spread by eating certain meats like fish tapeworm from eating fish or pork tapeworm from eating pig.

So we have to think, what’s special about the life cycle? And how might that fit in with what we know about the medieval period? Now written sources from the time do talk about how people would fertilize their crops and their gardens with manure from animals, just as people often do today. But it was just as common then to use human feces to fertilize your food and your crops as well.

So people would dig out the cesspits when they became full because someone’s got to make the toilet usable again. And then they would fertilize their crops with it. Now, because they didn’t understand about infectious diseases and the fact that worms could be spread with fresh feces, they would fertilize the crops straightaway rather than manuring it as the World Health Organization recommends today because if you manure the feces for a year or so, most of the parasite eggs die, and it’s much safer to do that.

So that might explain why the friars had a higher level of parasite infection than the general public because if they had a nice latrine block, and if they were emptying out their latrines onto their friary gardens once a year when they were filled up, then that might lead to reinfection of the friars with the parasites that we’re seeing. And that might have explained why they had more parasites than members of the general public, who may not have had a toilet at all or may not have been in a position to use their cesspit contents to actually fertilize their own garden.

ROXANNE KHAMSI: So what’s so interesting to me is that you’re studying historical parasites. What is it about these ancient parasites that is going to help us understand our world today?

PIERS MITCHELL: Well, many people are fascinated by our ancestors and the lives they lived and the health that they had, but it also helps us to understand the impact of the modern public health interventions that we take for granted so that now, everyone expects that the water that comes out of their tap will be clean and healthy. They expect the food they buy in the supermarket to be clean and ready to eat. Everyone expects their children to survive to be a good age, whereas in the past, people expected most of their children to die before adulthood.

So if we can study people who lived before all these public health interventions that we take for granted and then show the health consequences among people, then it hopefully reminds modern people why they should be washing their hands and why, if they go on holiday to places that don’t have such good sanitation, they have to take extra care with the water they drink. They have to make sure they wash their hands, have to make sure they have cooked food rather than salads, because otherwise, they will be at risk of getting the kind of parasites that the Augustinian friars did back in the medieval period.

ROXANNE KHAMSI: Well, that was really interesting, and it’s all the more reason for us to remember these days to wash our hands, not that we need a reminder. Thank you so much.

PIERS MITCHELL: Lovely to talk to you.

ROXANNE KHAMSI: Dr. Piers Mitchell runs the Cambridge Ancient Parasites Laboratory and is a senior research associate in the McDonald Institute for Arachaeological Research at the University of Cambridge.

Copyright © 2022 Science Friday Initiative. All rights reserved. Science Friday transcripts are produced on a tight deadline by 3Play Media. Fidelity to the original aired/published audio or video file might vary, and text might be updated or amended in the future. For the authoritative record of Science Friday’s programming, please visit the original aired/published recording. For terms of use and more information, visit our policies pages at http://www.sciencefriday.com/about/policies/