Steve Mirsky:    Welcome to Scientific American's Science Talk posted on January 12, 2016. I am Steve Mirsky. On this episode:

Piers Mitchell:   There was surprisingly no job in intestinal parasite infections during Roman period compared with the previous period, where you didn't have any toilets, so that was really surprising.

Mirsky:               That's Piers Mitchell. He's in the Department of Archaeology and Anthropology at the University of Cambridge. He studies the interactions between humans and parasites during evolution, as well as parasites in past civilizations and how they have affected human health. He's the author of the 2015 book Sanitation, Latrines, and Intestinal Parasites in Past Populations and he's just published a paper in the Journal of Parasitology titled "Human Parasites in the Roman World: Health Consequences of Conquering an Empire."

                           Evolution, parasites, and Ancient Rome are all favorite subjects of mine, so as soon as I saw the title of the paper I got in touch with Mitchell. I asked him to talk about the research and its counterintuitive findings. He sent me a five-minute voice recording via e-mail. I was originally planning to pull a quote or two for our shorter podcast, 60 Second Science, but his entire mini-lecture is so good I decided to just play it all for you straight through. Here's Piers Mitchell.

Mitchell:             So the Romans were very well known for the sanitation that they developed and spread across the Roman Empire, so before the time of the Romans we don't see toilets and things like that in Iron Age and Bronze Age Europe. But the Romans introduced these technologies where we have multi-seat public latrines with handwashing facilities and sponges to wipe yourself after you've been to the toilet. And they had sewers to take the feces away under the roads to be disposed of elsewhere. They also had clean drinking water from aqueducts and laws that involved taking rubbish and feces out of towns to try and make them cleaner.

                           So we would think that all these things would improve health of people under Roman rule, especially when it comes to those parasites that might be spread by poor sanitation and contamination of your town by feces. So I looked at the different evidence that we can see for how this would have affected health in the past. So we looked at endoparasites; these are parasitic worms and single-cell parasites that cause dysentery, for example, and looked at all the archaeological evidence for these right across the Roman Empire compared with the evidence in the Bronze and Iron Age, but before the Roman Empire.

                           We also looked at the ectoparasites, looking at how common fleas and body lice and head lice and so on were. And we looked for changes over time, 'cause we thought that Roman baths, which would clean your skin and clean your hair regularly might potentially cut down on the number of ectoparasites that people would have in the Roman period. We can look at that archeologically, too.

                           And what I found was that there was surprisingly no drop in intestinal parasite infections during Roman period compared with the previous period, where you didn't have any toilets. So that was really surprising, because modern research suggests that having toilets should cut down on these parasites. And we think that one possible explanation for this could be that the collection of the feces and rubbish from towns under Roman law was then taken out to fertilize the crops, which gave you more plants, but unfortunately resulted in recontamination of the population, because the human feces then got onto the plants that were then eaten again. So it may be that these very sanitation laws about keeping streets clean actually led to reinfection of the population, which was obviously not quite what they had in mind.

                           The other thing we found was that the use of Roman baths doesn't seem to have cut down on the prevalence of parasites on the skin and hair either. So if you compare the number of ectoparasites, such as body lice and fleas, they were just as common in Roman period York, for example, as it was in Viking and medieval period York in Britain. And so Vikings in medieval period didn't go to the baths regularly, Romans did, but we still have just as many body lice and fleas. So washing doesn't seem to have cut down on ectoparasites during the Roman period either.

                           The other fascinating thing I found was that the fish tapeworm seems to become much more common across the Roman Empire compared with in the Bronze and Iron Age before the time of the Romans we see relatively low levels of fish tapeworm. And one possibility to explain this is that the Romans were very fond of an uncooked fermented fish sauce called garum. And this was made in northern Europe and then spread across the Empire, because it was put in sealed jars, which could then be traded right around the Empire. So it could be that this garum fish sauce was able to spread fish tapeworm from northern Europe right across the Empire into areas where the fish tapeworm wasn’t previously endemic. So it looks like this might be an example of the culinary ideas of the Romans being spread across their empire and consequently more people getting infected with parasites. So we could argue that this was a bad health consequence of conquering an empire.

                           So it's not to say that toilets and drains and things were bad in any way, they would certainly have helped with smells. It would mean you wouldn’t have to pop home if you were out shopping in town, you could have used the public latrines, which would have been a good idea. And similarly, public baths would have made people smell less and make them cleaner. But neither of these things seem to have actually had a health benefit when it comes to infections such as parasites. And that’s a particularly unexpected finding but one that the evidence seems to be pretty convincing for.

Mirsky:               That's it for this short episode. Get your science news at our Web site, www.scientificamerican.com, where you can track down my 2013 column, headlined "Toilet Tissue: Anthropologists Uncover All the Ways We've Wiped," also about ancient bathroom habits, as you might have guessed. For example, the Greeks had a saying that "three stones are enough to wipe." And follow us on Twitter, where you'll get a tweet whenever a new item hits the Web site. Our Twitter name is @sciam. For Scientific American Science Talk, I'm Steve Mirsky. Thanks for clicking on us.