Schistosomiasis (Bilharzia)

Magnified image of Schistosoma mansoni trematodes

Schistosoma mansoni trematodes

Credit: CDC

Schistosomiasis, also known as bilharzia, is a neglected tropical disease caused by parasitic worms. It is second only to malaria as the most devastating parasitic disease. The parasites that cause schistosomiasis live in certain types of freshwater snails. The infectious form of the parasite emerge from the snail and then contaminate the water. People become infected when their skin comes into contact with the contaminated freshwater. Most human infections are caused by Schistosoma mansoni, S. haematobium, or S. japonicum.

Why Is the Study of Schistosomiasis (Bilharzia) a Priority for NIAID?

Although schistosomiasis is not found in the United States, more than 200 million people are infected worldwide.

How Is NIAID Addressing This Critical Topic?

NIAID-supported researchers are studying many diverse aspects of schistosomiasis to find new ways to prevent and treat the disease. Due to the unique lifecycle of the schistosome, the parasitic worm that causes schistosomiasis, researchers can study the disease and its debilitating effects during various stages: the waterborne egg stage, the intermediate snail host, or the parasite’s adult phase which takes place in humans. With the recently sequenced genomes of multiple species of schistosome parasites, researchers can move forward in developing valuable vaccines and therapeutics for schistosomiasis.

To learn about risk factors for schistosomiasis and current prevention and treatment strategies visit the Centers for Diseases Control and Prevention (CDC) schistosomiasis site.


A safe and effective vaccine is an important part of controlling the transmission of schistosomiasis. Researchers are currently working on improving the efficacy of identified vaccine candidates and are also conducting studies to better understand the mechanisms by which those vaccines elicit an immune response in animal models.


Recently, the genomes of two schistosomiasis-causing parasites were sequenced: Schistosoma mansoni and Schistosoma japonicum. The information from the analysis of these genomes may help researchers find new ways to treat the disease. For example, investigators have begun to uncover the metabolic reactions that are encoded in the worm’s genetic sequences. As a next step, it may be possible to design a drug that disables the identified metabolic processes, thereby inhibiting the schistosome’s development.


Public health experts are concerned about schistosomes becoming resistant to the currently used drug, praziquantel. If this were to occur, an alternative drug would be needed as a substitute. To fulfill this need, NIAID-supported researchers are conducting basic research to learn more about certain biochemical pathways that the schistosome worm requires for survival. If a drug could target these pathways and inhibit them, this would be a new and effective way to eliminate the parasite. 

Video: Scientists studying schistosomiasis rely on NIAID for an unusual research resource—snails.

Content last reviewed on August 12, 2012