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Snails can travel far, spreading disease, researchers find

I would expect it to take all day for a snail to get across my backyard and its entire life to get around my neighborhood.

But according to a new study led by a researcher from the University of California, Berkeley, certain types of freshwater snails can travel distances of almost 30 miles, spreading a potentially deadly parasitic disease as they go.

"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, PhD, an associate professor of environmental health sciences at UC Berkeley and lead author of the study, in a recent news story.

These snails carry parasites that cause schistosomiasis -- a disease that affects more than 200 million people worldwide, most of whom live in rural communities in developing countries. The parasites develop and multiply inside the infected snails, then enter the water and penetrate the skin of people who are swimming or bathing. Within several weeks, the parasites mature into adult worms that infect the body's blood vessels, bladder and intestines.

The movement of one parasite-carrying snail can spread the disease to a new area. That's why the multi-institutional research team studied snail migration in the rural region of Sichuan, China, where schistosomiasis incidence has increased in recent years. The researchers collected and analyzed the genetic makeup of over 800 snails from 29 sites in Sichuan, as recently reported in PLOS Neglected Tropical Diseases.

The study found that between 14 to 33 percent of sampled snails had recently migrated from another location, and some had traveled as far as 27 miles. How did these slow-moving animals get that far, when their average lifespan is only 171 days? Researchers discovered that the shelled creatures can grab a ride on vegetation in waterways, cling to agricultural products such as rice, or get carried by birds or other animals.

The authors hope that an improved understanding of how and where these snails migrate will help others design better control measures to limit their movement and the spread of schistosomiasis.

Previously: To control schistosomiasis, Stanford researchers advise thinking beyond pillsScientists call for end to devastating worm diseases and A moment in the sun for the tsetse fly - and the Stanford researcher studying its effect on Africa
Photo by freshidea

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