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The blood fluke, or the Schistosoma mansoni, may not be a household name, but its presence is felt in many homes. According to the World Health Organization, 230 million people in the world need treatment for the chronic disease that the parasite causes each year. Research has found that the parasite can remain inside its human hosts for decades - and, for the first time, researchers have discovered that stem cells explain how.

"We started with the big question: how does a simple parasite survive in a host for decades?" study author Phillip Newmark said in a statement. "That implies that it has ways of repairing and maintaining its tissues. This study gives us insight into the really interesting biology of these parasites, and it may also open up new doors for making that life cycle a lot shorter."

Blood flukes live a long and gruesome life. Their eggs hatch in water that has been tainted with feces, and then the larva grow in the bodies of snails. From there, the young blood flukes enter human bodies by burrowing into human skin and taking residence inside the person's veins.

If the fluke is a female, they then start laying eggs, almost continuously, on a daily basis. If the eggs are not excreted out through the person's feces, they can become lodged into the person's organs and tissues, particularly the liver. The eggs can trigger inflammation, which is particularly problematic for children, who are considered especially at risk for infection and can even experience delays in growth and brain development as a result.

Researchers found that the parasites were loaded with undifferentiated cells that were housed in the mesenchyme, which is a loose connective tissue that surrounds the organs. These cells also had the ability to duplicate their DNA and split into daughter cells.

The researchers labeled the cells with fluorescent markers. They found that some of the cells migrated to different areas of the body to become part of those tissues. They also identified a gene that differentiated the dividing cells from the non-dividing ones. When they turned off the gene, the dividing cells died out.

The study was published in the journal Nature.