A new research indicates that parasite-carrying snails can travel long distances, up to 27 miles, or 44 kilometers, spreading a deadly disease along the way.
Led by a researcher with the University of California, Berkeley, the study published in the journal PLoS Neglected Tropical Diseases was the first to find genetic evidence for long-distance movements among snails that pose an important public health threat.
"We don't think of snails as particularly mobile, but the genetic evidence we found that snails can traverse substantial distances is a reminder of just how difficult it is to contain and control infectious diseases carried by animals and insects," said Justin Remais, an associate professor of environmental health sciences at UC Berkeley.
Freshwater snails transmit schistosomiasis, a parasitic disease that affects more than 240 million people worldwide.
Each snail can contaminate the water that people work, swim or wash in with many parasites, so movement of just one snail to a new area could introduce the disease in a previously healthy population. Therefore, understanding how disease-carrying snails move is critical for designing ways to limit their spread.
For the study, researchers traveled to villages in Sichuan Province, southwestern China, and collected and analyzed the genetic makeup of hundreds of snails that carry parasites.
They collected snails from their natural habitat along waterways that crisscross rice and other agricultural fields, and then analyzed the genetic material from these snails in labs at the China Centers for Disease Control and Prevention and at Justus Liebig University in Giessen, Germany.
While the snails' genetic information suggested nearly one-quarter of the snails in the study had migrated from another location, the evidence for long-distance movement suggested the snails travel both under their own power and with a significant helping hand, namely by rafting on vegetation in water, being transported in agricultural products and getting carried by birds or other animals.
In addition, the study found that human modifications to the landscape may determine where snails move. Movement was most likely to occur across land that had been developed for agriculture, and areas with expansive irrigation networks were most likely to receive and retain migrating snails.
"Changes to our environment can facilitate or limit the spread of vectors and hosts, and so we need research that helps us fully understand the consequences of human activities for the spread of the diseases they carry," Remais said in a news release from UC Berkeley this week.
