The latrines were uncovered during digs in the Old City of Jerusalem dating from the 7th to 6th centuries B.C., when Jerusalem was the capital of the Assyrian empire-controlled kingdom of Judah. Feces samples came from pit toilets at two building complexes that would have been inhabited by the city’s richest residents.

“Dysentery is spread by feces contaminating drinking water or food, and we suspected it could have been a big problem in early cities of the ancient Near East due to overcrowding, heat and flies, and limited water available in the summer,” said Piers Mitchell, a biomolecular archaeologist and honorary research associate in the University of Cambridge’s archaeology department, in a news release.

Mitchell, a co-author of the study, said the discovery of the dysentery-causing parasites suggests they were widespread in the kingdom at the time.

Ancient medical texts suggest that was the case. But since dysentery-causing parasites are fragile and hard to detect in fecal samples, Giardia eluded past researchers.

In this case, the archaeologists used biomolecular analysis to reveal its presence in the ancient feces they recovered at both latrines. In the lab, they used ELISA (enzyme-linked immunosorbent assay), which uses antibodies to pinpoint the presence of specific proteins in a sample.

Researchers already knew that the ancient Judeans faced infections with parasites such as tapeworm. The current analysis not only found Giardia but also ruled out other suspected diarrhea-causing parasites Entamoeba and Cryptosporidium.