In what is now northern Syria, researchers have found the earliest known evidence of infection with a parasitic worm that now afflicts more than 200 million people worldwide.
     Archaeologists who discovered a 132-micrometer-long parasite egg near the pelvis of a child's skeleton in a Mesopotamian graveyard say it dates to a time when societies first used irrigation systems to grow crops. The Ubaid people who lived in Tell Zeidan between 6500 and 6000 years ago are known to have pioneered the use of irrigation to grow food on their arid land. Living near and working in those canals could have put them in the parasite's path, allowing it to jump from its temporary hosts - freshwater snails - to people's intestines, as it continues to do in Africa, Asia, and South America.
     Before this discovery, the oldest confirmed case of schistosomiasis was a 5200-year-old mummy in Egypt.
     According to team leader and palaeo-pathologist Piers Mitchell of the University of Cambridge UK, "A lot of different parasites - roundworms, hookworms, whipworms - find it difficult to infect you if you are moving a lot of time." Nomadic groups remain small, don't stick around long enough to contaminate any one water source, and tend not to keep domestic animals such as sheep and dogs, which can be sources of parasites. When humans turned to agriculture, populations grew past the critical thresholds that infectious diseases require to sustain themselves.
     Gil Stein, a professor of Near Eastern archaeology at the University of Chicago and one of the report's authors, said that irrigation might have also spurred outbreaks of other diseases such as malaria. Other experts agree it was likely that irrigation spread parasitic diseases beginning in ancient times.
     Scott Lawton, a parasitologist from Kingston University London, cautions against drawing too many conclusions from a single egg. "It could have been through irrigation, it could have been through natural waterways, it may have even been an infection picked up from travelling elsewhere in the Middle East or North Africa. There is certainly more work to be done to disentangle the causes of infection in the Syrian gravesite."

Edited from Science Magazine (19 June 2014), The News International (21 June 2014)