Researchers have found evidence of a parasitic infection in the skeletal remains of an individual that lived between 6,500-6,000 years ago in an early farming settlement of northern Syria. The discovery represents not only the earliest example of human infection with this particular parasite, but also the first demonstration that advances in technology could have encouraged the spread of disease. The study has been published in The Lancet Infectious Diseases.
Schistosomiasis, also called bilharzia, is a disease caused by trematode flatworms belonging to the genus Schistosoma. Individuals can become infected if they come into contact with larval forms of the parasite, called cercariae, which are released by certain types of freshwater snails. The larvae then develop into adult worms which reside in the blood vessels.
Once mature, the females produce eggs that are shed in the urine or feces but some can become stuck in the intestines or bladder, causing a variety of ailments if untreated such as kidney failure and bladder cancer.
Before now, the earliest archeological example of schistosome infection was found in ancient Egyptian mummies that dated as far back as 5,200 years ago, but no one knows when this parasite started infecting humans.
Researchers made this recent discovery after excavating human remains from Tell Zeidan in northern Syria, which was an early settlement of farmers dating between 7,800-6,000 years ago. The team collected samples from several regions of the body, including where the intestines and bladder would have been, and examined them under the microscope.
A schistosome egg was discovered in a pelvic sample from one of the individuals which suggested that they were infected with the parasite. No eggs were found in the control samples, indicating that contamination by modern populations was unlikely.
The team postulates that while the individual could have contracted the parasite by strolling or bathing in freshwater, they may have picked up the worm from man-made irrigation systems that were introduced into the area some 1,500 years before to improve crop production.
“Studies in Africa in modern times have shown that farming, irrigation and dams are by far the most common reasons why people get Schistosomiasis,” Dr. Piers Mitchell, study author and anthropologist at the University of Cambridge, told Live Science.
Although no direct evidence for such irrigation systems has been discovered, researchers found remnants of domesticated wheat and barley in the area. Tell Zaidan is far too dry to support the growth of these crops which suggests that settlements likely used irrigation to help them grow.
The researchers therefore hypothesize that crop irrigation employed thousands of years ago in the Middle East enabled the spread of schistosomiasis into humans living in this area, prompting the immense disease burden that still occurs today.