The researchers found one egg in the soil around the abdomen and pelvis of a child's skeleton. By contrast, they didn't find any around the head or the feet — suggesting that it came from the person in the burial site, and not from some later person who urinated or defecated at the same site.
Although the centuries have wiped away any traces of irrigation technology at Tell Zeidan, remnants of wheat and barley were found at the site.
"There was not enough rainfall for barley to grow by itself, but it would have flourished with irrigation," Stein told Live Science.
The site also lies on a floodplain where the Euphrates and Balikh Rivers meet.
When the rivers overflowed their banks, water would have spread across the adjacent plains, and inhabitants may have built little mud retaining walls to keep the water on the fields for longer. (Even today, farmers along Egypt's Nile River use similar irrigation methods).
The farmers could have waded into the water-covered fields, to do weeding and planting, and the rivers' warm, slow-moving water would have been an ideal breeding ground for the snail hosts of the parasite, Stein said.
As follow-up work, the team wants to analyze the genetic material from the parasite to see if the flatworm has evolved since it began infecting humans, Mitchell said.
The findings were published today (June 19) in the journal Lancet Infectious Diseases.
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