Schistosomes are flukeworms that belong to the genus Schistosoma and the class Trematoda. Their life cycle is simple and very insidious (gradual and stealthy). The parasite eggs excreted in animal and human urine and feces contaminates freshwater ponds, lakes and rivers, where they break open into a developing stage called miracidium. Snails get infected by these larval forms of the parasite. The larvae keep developing in freshwater snails, emerging from the snails into the water.
They enter the human body either in drinking water or by boring directly into the skin. Then, they migrate into large blood vessels and cause local hemorrhages as they lay their spined eggs. Today, more than 110 million human beings in tropical countries have schistosomes in their blood and are doomed to a wasting and debilitating disease called schistosomiasis. Wherever schistosomes are present, it is dangerous to bathe and wade in fresh water and harzardous to drink untreated water.
Each year, millions of Asians standing barelegged in flooded rice paddies pick up the disease as they plant their rice. In the Middle East, the construction of new dams, which we usually think of as a progress, has created new breeding places for snails and schistosomiasis is on the rise. The disease will only be reduced when we control the snail population.
Schistosomiasis is characterized by rash at the site of entry, diarrhea, fever, fatigue, enlargement of the liver, which may develop cirrhosis. The disease is effectively treated with a drug praziquantel.