Researchers have discovered what they believe is the oldest ever schistosomiasis parasite egg in a 6,200-year-old grave by the Euphrates river in Syria, potentially providing the first evidence that Middle East agricultural irrigation systems – the artificial application of water to land or soil – may have contributed to the schistosomiasis burden.
Schistosomiasis, also referred to as bilharzias or snail fever, is a disease caused by parasitic trematode flatworms that live in specific types of freshwater snails. Schistosomiasis can cause anemia, kidney failure and bladder cancer in humans. The disease has even been associated with infertility.
More than 200 million people worldwide are infected with the disease, although the flatworms that cause the condition are not found in the US. According to the World Health Organization (WHO), schistosomiasis is most common in tropical and sub-tropical areas, particularly in poor communities that do not have adequate sanitation and access to safe drinking water.
Freshwater in rivers and lakes can become contaminated by the infectious form of the parasites, known as schistosoma parasites. Humans can become infected with the parasites if the skin comes into contact with contaminated freshwater.
Once infected, the parasites can mature into adult worms that live in the blood vessels of the body. The female worms produce eggs in the blood vessels, and some of these eggs travel to the bladder or intestine and pass through urine or stools.
It is one of these eggs that the research team – including Dr. Piers Mitchell of the University of Cambridge in the UK – discovered in the pelvic area of an individual buried in a 6,200-year-old grave at Tell Zeidan in Syria, a country where schistosomiasis is common.
Prior to this discovery, the oldest schistosomiasis parasite egg on record was found in a 5,200-year-old Egyptian mummy. This latest discovery shows that the schistosoma parasite infected humans more than a thousand years earlier.
But perhaps most notably, the grave was discovered on the banks of the Euphrates river. Dr. Mitchell told Medical News Today that the seeds of certain crops found near the site would not have grown successfully with the rainfall in that region alone, suggesting that some form of agricultural irrigation may have been used.
Explaining the relevance of this, Dr. Mitchell said:
“Schistosomiasis has to spend part of its life cycle in water snails, and people contract the disease by wading in that water. Evidence from across the Middle East suggests various forms of crop irrigation started to be introduced there from 7,500 years ago.
It seems likely that in the following centuries, the schistosomiasis parasite became endemic in the region, infected the water snails and spread to people wading in these crop irrigation systems.”
But what does this discovery tell us about the present-day schistosomiasis burden?
Dr. Mitchell told us that evidence suggests new water technologies – such as dams and open water irrigation channels in Africa – are rapidly becoming colonized by freshwater snails, which is contributing to the schistosomiasis endemic
“There is a strong argument that people in Africa need to use different approaches to water management to prevent people wading in these water sources,” he added. “That would break the cycle of disease spread.”
He said the team is working with archaeologists who are in the process of excavating towns in the ancient Middle East, in the hope of studying ancient parasites in that area. “In this way,” he continued, “we hope to show the effects upon disease that resulted from nomadic hunter gatherers settling down and making their living by farming crops and herding animals.”
In addition, the team hopes to look at how the creation of early sanitation technology, such as latrines, affected the spread of parasites.
Medical News Today recently reported on a study published in PLOS One, which detailed the creation of a test that may be able to diagnose schistosomiasis.