The worm has turned
Schistosomes belong to the class Trematoda. They are parasitic flatworms with complex life cycles that involve infecting at least two hosts. The primary host, where the flatworms or flukes sexually reproduce, are vertebrates, including humans. The intermediate host, which is employed to disperse the parasite, is usually a snail.
In the image above by Bo Wang and Phillip A. Newmark of the University of Illinois at Urbana-Champaign (which won a 2013 BioArt award from the Federation of American Societies for Experimental Biology), developing Schistosoma mansoni larvae (center) are shown developing inside the muscular, fibrous tentacle of a snail host.
Eventually these larvae are released into water. If the contaminated water comes into contact with human skin, the larvae penetrate and ultimately develop into adult worms residing in veins of the urinary tract and intestines, causing a condition known as schistosomiasis, which affects almost 240 million people worldwide.
The infection is prevalent in tropical and sub-tropical regions, in poor communities without potable water and adequate sanitation. There are many potential complications of schistosomiasis, including gastrointestinal bleeding, renal failure, infertility, pulmonary hypertension and sepsis. Typical treatment involves the drug Praziquantel, an anthelmintic that causes the flukes to be expelled from the body. The disease can become chronic, and in some regions, acute schistosomiasis is associated with a mortality rate of up to 25 percent.