The law of unintended consequences may have a longer history than we thought. At a Neolithic settlement in the region where early farmers pioneered crop irrigation systems, a team has found the oldest example of a water-borne disease that today affects 210 million people worldwide.
Schistosomiasis is caused by parasitic flatworms, contracted when humans wade in warm freshwater inhabited by snails that carry the parasite. It can lead to anaemia, kidney failure and death.
A new find from Tell Zeidan, a site in northern Syria, suggests the disease was also a problem in ancient times.
Piers Mitchell at the University of Cambridge and his colleagues examined sediment collected from beneath the pelvises of 26 skeletons, all between 6500 and 6000 years old. In one 6200-year-old sample they found a 130-micrometre-long flatworm egg that belonged to one of the species responsible for schistosomiasis.
"We have identified the earliest case of schistosomiasis so far in the world," says Mitchell.
Evidence of the disease has also been found in 5200-year-old Egyptian mummies.
Stagnant water
What makes the new find particularly significant is that it comes from an individual who lived in the Fertile Crescent, where crop irrigation was invented just 1000 years earlier. The research team believes crop irrigation was used in Tell Zeidan because archaeological evidence suggests water-hungry crops were able to grow in the otherwise arid landscape.
We know from modern research in several African countries that crop irrigation plays a key role in the spread of schistosomiasis. "All these points support the idea that crop irrigation in the Middle East would more than likely have facilitated the spread of schistosomiasis in these ancient civilisations," he says.
The find is extremely exciting, says Scott Lawton at Kingston University London, because the archaeological record of ancient human parasites is otherwise very meagre. However, he points out that although it's possible the individual caught an infection from an irrigation system, they may simply have caught it from fishing or washing in a natural body of water. "As a parasitologist – not an archaeologist – I think there is certainly more work needed to be done in order to disentangle the causes of schistosome infection in the Syrian gravesite," says Lawton.
The nature of the irrigation system used may have made human contact with irrigation water particularly likely, says Gil Stein, an archaeologist involved in the study based at the University of Chicago. "Irrigation in the Zeidan area probably took the form of what is called floodwater recession irrigation". This involves flooding large areas of farmland with standing water, rather than confining the water to narrow irrigation channels.
Those large bodies of warm standing water would have been an ideal breeding ground for the infection, and difficult for the farmers to avoid contact with, he says.
Journal reference: The Lancet Infectious Diseases, DOI: 10.1016/S14733099(14)707947
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