Medieval bathrooms reveal that people were infested with parasites back then 

What could you possibly find in a toilet that’s been out of order for hundreds of years? Some ghastly things might be hiding in there, and it’s not what you might think.

There were obviously no porcelain seats or advanced plumbing in latrines 800 years ago. You went, and countless others went after you, unknowingly leaving behind evidence of what was crawling in an entire community’s guts. Think of all those TV commercials that relentlessly insist on probiotics for gut health. Probiotics might be trending, whether in pill or yogurt form, but they do help balance the intestinal microbiome—everything that lives in your guts. Scientists have now been able to find out what was lurking in the microbiomes of two cities during the 14th and 15th centuries, and it’s ugly.

Parasites thrive when you don’t have proper sanitation. The Middle Ages spawned the bubonic plague, so it has nowhere near the cleanest reputation in history. Cesspits from Jerusalem and Riga, Latvia are giving us a closer look the microbiomes of pre-industrial agricultural societies that might be able to provide insight into our own insides. While industrialization has been associated with inflammatory bowel disease, food allergies and obesity, microbial DNA in coprolites (fossilized feces) recovered from long-abandoned latrines has revealed that Medieval human microbiomes were plagued by parasites.

“Together, these findings provide a first glimpse into the rich prokaryotic and eukaryotic intestinal flora of pre-industrial agricultural populations, which may give a better context for interpreting the health of modern microbiomes,” said Kirsten Bos, a specialist in ancient bacterial DNA from the Max Planck Institute, who recently co-led a study published in Philosophical Transactions of the Royal Society B.

Gnarly things revealed themselves under the (literal) microscope. The eggs of parasitic worms were easily detected with microscopic analysis, but there were other gut microbes impossible to make out. This is where aDNA (ancient DNA) analysis came in. Surprisingly, there was much that had been preserved in centuries-old latrine gunk, including both beneficial and harmful bacteria, protozoa, fungi, and, of course, parasitic worms. Some of the parasites identified were protozoans Entamoeba hystolitica and Giardia duodenalis along with whipworm, roundworm, two species of tapeworm.

“Impressively, DNA preservation extends beyond molecules protected within resilient physical structures such as parasite eggs,” Bos said. “Signals of gut flora are detectable, though microbial content is heavily influenced by depositional context.” 

Being infected with E. hystolitica feels like food poisoning, but is easily squashed by antibiotics. T. trichiura or human whipworm is food poisoning on steroids. These tiny monsters chew away at intestinal tissue and lay their eggs in the colon before exiting with the stool and getting flushed. Those eggs hatch into more worms, which perpetuate the cycle by mating and laying eggs before they go down the drain. The creepy sensation of something gnawing at your guts should not be ignored, and they can even cause cysts in the intestine if too many of them are partying in there. The only way to exterminate these things is a combination of powerful anti-parasitics that make you feel zombified.*

Meaning, people who lived during the Middle Ages must have really suffered without modern medicine, having to rely on tonics and elixirs that were mostly snake oil.

The most reliable method of unearthing parasites was morphology. Being able to see parasitic worms or their eggs made them immediately obvious, though some species lay extremely similar eggs. Even then, the scientists may have not gotten the most accurate read on which of these parasites were the most common because some eggs are extremely fragile and cannot survive so many centuries sitting at the bottom of what once passed for a toilet.

Visibility was out of the question for eukaryotic pathogens. Eurkaryotes are microbes whose cell structure includes a nucleus with a membrane. Such pathogenic organisms, like protozoa, could not be seen with light microscopy, so the research team had to rely on genetic data. What may be surprising is that there was no more of any bacterial gut species in one city than the other. Non-parasitic Ruminococcus bromii, which break down starch in the colon, were the most common bacteria found across microbiomes. This could either mean that they were really abundant or that other species with higher populations could have broken down over time.

“It is plausible that DNA fragments of eukaryotic parasites…were not identifiable using current databases, because they belong to portions of the genome that have not yet been assembled,” Bos said.

Medieval microbiomes also turned out to be very different from modern human microbiomes. When you start cooking your food more thoroughly and spraying disinfectant all over the place, not to mention getting caught in the fast food trap we are all susceptible to, things inside are going to change. Further study of both these and other cesspits could tell us past habits that could possibly help with the most pervasive gut issues we face now.

So, should you listen to those commercials and take a probiotic? There is actually no definite answer for that, but to escape parasites, be sure to check reviews on questionable restaurants and send back anything that looks suspicious.