Parasites are typically a rather private matter. And so, for that matter, is defecation. So likely never in their wildest dreams did the Loma San Gabriel people (in what is now Mexico), who answered nature’s call in a cave more than 1,000 years ago, imagine that future humans would be sifting through their droppings looking for clues.
Feces is an open window into the many other organisms living in our bodies—from beneficial bacteria to harmful parasites. The genetic material from these other life forms makes its way out into the world via our own output. So scientists can and do go hunting there for familiar (or unfamiliar) DNA sequences, for a variety of reasons. (Wastewater treatment plants, for example, have been key places to monitor for local COVID-19 surges.)
But while information-rich in the present, DNA, like most biological materials, has a way of degrading over time. So finding such small traces of it from pathogens in ancient excrement can be challenging. Researchers behind a new study, published in PLoS ONE, used PCR testing, and additional sequencing, to see what they could find in a collection of 10 different samples of paleofeces collected from La Cueva de Los Muertos Chiquitos in the Rio Zape Valley in Mexico. The remnants had been deposited approximately in 725-920 A.D.
Pathogens and parasites, it turned out, were exceedingly common in people living in that area then. For example, the vast majority of samples revealed that the human defecator was harboring E. coli, and six of the 10 studied were infected by pinworm.
The study served as proof of concept that many of these ailments could be detected using this particular technology—even in very old feces. As such, the team had a list of 30 well-known gut microbes and pathogens they were looking for. Future studies could go hunting in dung piles for lesser-known, or perhaps even novel ones.
“Working with these ancient samples was like opening a biological time capsule,” Drew Capone, an assistant professor in the School of Public Health at Indiana University, said in a statement. “Each one revealing insight into human health and daily life from over a thousand years ago.”
Who knows what clues could come next, that had been buried in ancient poo. 
Lead image: BRO.vector / Shutterstock
