Antique parasite worms its way into human history

PARIS: Forensic sleuths said Thursday they had found the oldest known egg of the bilharzia parasite, revealing how human advancement enabled a tiny freshwater worm to become a curse for millions.
In a letter published by the journal The Lancet Infectious Diseases, a team of archaeologists and biologists said they found a 6,200-year-old egg of the feared intestinal parasite in an ancient grave in northern Syria.
The site, Tell Zeidan, is in the valley of the Euphrates — part of the fabled “Fertile Crescent” where humans settled down to farm nearly 8,000 years ago, making the historic leap from hunter-gatherer.
The team excavated the skeletal remains of 26 people from the burial site and gently sifted through sediment collected from the pelvic area of each. The painstaking work turned up an egg just 132 millionths of a meter long that under a powerful microscope turned out to be pale brown, stained by millennia-long exposure to the soil.
The egg, say the researchers, is from one of two species of schistosomes — flatworms that cause bilharzia, which affects hundreds of millions of people in tropical Asia, Africa and Latin America.
Schistosomes burrow into the skin when someone wades into freshwater, and develop into adult worms before invading the kidney and bladder or intestines.
Luxuriating in the balmy flow of blood, they mate, and their eggs are excreted in urine or faeces, thus exposing more people to the disease, which is also called schistosomiasis or snail fever.
Infection — typically signaled by blood in the urine — can result in kidney failure, bladder cancer, malnutrition and anaemia.
Recent DNA analysis of schistosomes suggested the flatworm evolved in Asia and spread from there to Africa and beyond.
But how this happened was unclear until now.
Migration through early human settlement in the Middle East, via the irrigation system of the Fertile Crescent, is a likely answer, according to the letter.
The people at Tell Zeidan grew wheat and barley in highly arid conditions, which suggests they developed an irrigation system to water their crops, it says.