Your Guide to
Neglected Tropical Diseases

Schistosomiasis is a parasitic disease of tropical and subtropical regions, where rivers, lakes, and ponds are central to daily life, with fresh water used for bathing, washing, fishing, and play. This regular contact with fresh water is how the disease spreads: tiny parasites released by infected snails living in the water penetrate people's skin during these everyday activities. If left untreated, schistosomiasis can cause serious long-term health problems due to the large number of eggs produced. These problems may include blood in the urine, liver and kidney damage, bladder cancer, infertility, and, in some patients, serious chronic complications associated with high mortality. Children with untreated schistosomiasis often suffer from malnutrition, anemia, stunted growth, and learning difficulties that affect their education and future opportunities.

Three types of freshwater snails act as vectors for schistosomiasis. The cycle begins when someone infected with schistosomiasis goes to the bathroom in or near freshwater, whether because they lack proper toilets or because they're washing or working near the water. Microscopic parasite eggs enter the water, hatch, and seek out the specific snail species that can host them. Inside the snails, the parasites multiply over several weeks. The snails then release these parasites back into the water, where they can survive for about two days, waiting for a human host. When people wade, swim, bathe, wash clothes, fish, or just walk through this contaminated water, these tiny parasites burrow through their skin (often without the person feeling anything) and enter the bloodstream, growing into adult worms inside the body and produce eggs, which are passed in urine or feces, starting the cycle all over again.

Geographic scope:

• Reported in over 75 countries worldwide, with more than 50 requiring large-scale treatment programs.
• Sub-Saharan Africa accounts for the vast majority of African schistosomiasis cases and Brazil has residual endemic areas.

Population affected:

• More than 250 million people were estimated to be living with schistosomiasis as of 2021, with 779 million at risk of infection.
• Nearly 50 million preschool-aged children were historically left untreated due to lack of appropriate medication for this age group (a gap now being addressed).

Praziquantel, available since the 1970s with high cure rates, has been donated by Merck to WHO for free distribution since 2007. Yet only about 30% of those needing treatment typically receive it. Until recently, 50 million preschool-aged children were excluded because tablets were too large and bitter. Treatment cures infection but doesn't prevent reinfection; people return to contaminated water for their daily needs. Without clean water and sanitation infrastructure, treatment alone cannot eliminate the disease.

A breakthrough came in 2024 when WHO prequalified new treatment, a child-friendly formulation of praziquantel for children aged 3 months to 6 years, developed by the Pediatric Praziquantel Consortium with support from the GHIT Fund. This dissolvable tablet tastes better, withstands hot climates, and achieves 90%+ cure rates. First treatments began in Uganda in 2025. In September of that year, arpraziquantel was added to the WHO Essential Medicines List as a therapeutic alternative to praziquantel for children, a milestone confirming its role as the standard of care for preschool-aged children globally.