Schistosomiasis (Bilharzia): WHO Reports 253.7 Million People Need Treatment as Waterborne Parasite Threatens Millions
Key Facts
- At least 253.7 million people required preventive treatment for schistosomiasis in 2024, with only 100.5 million actually treated WHO
- 93.9% of those requiring treatment live in Africa, making it predominantly an African health crisis WHO
- Schistosomiasis transmission has been reported from 79 countries worldwide WHO
- In 2024, only 39.6% of people requiring treatment were reached globally, with 61.7% coverage among school-aged children WHO
- WHO estimates approximately 14,353 deaths occur globally per year from schistosomiasis complications WHO
In December 2024, WHO released updated data revealing a troubling treatment gap: while a quarter-billion people needed preventive chemotherapy for schistosomiasis, 15 countries requiring preventive chemotherapy failed to carry out mass drug administration in 2024, including high-burden nations like Mozambique, Sudan, and Yemen GSA. The parasitic disease, transmitted through contact with contaminated freshwater, continues to devastate communities across Africa, the Middle East, South America, and Asia.
This waterborne illness doesn’t just sicken—it traps families in cycles of poverty, stunts children’s growth, and silently damages organs for years before symptoms appear. WHO’s 2021-2030 roadmap aims to eliminate schistosomiasis as a public health problem in all endemic countries, but as recent data shows, millions still lack access to the simple pill that could save them. This article examines what WHO knows about schistosomiasis, who’s most at risk, and why global health initiatives are struggling to reach those who need treatment most.
What Is Schistosomiasis? WHO’s Definition
According to WHO, schistosomiasis is an acute and chronic parasitic disease caused by blood flukes (trematode worms) of the genus Schistosoma WHO. The disease goes by several names—bilharzia, snail fever, and Katayama fever—but they all describe the same water-transmitted infection.
Here’s what makes it particularly insidious: people become infected when larval forms of the parasite, released by freshwater snails, penetrate the skin during contact with infested water WHO. You don’t have to drink the water. Simply wading through an infected stream while washing clothes or bathing is enough.
Once inside the body, schistosome larvae travel through blood vessels to the liver, where male and female worms pair up and move to veins around the intestinal tract or urinary tract depending on the species Wikipedia. The real damage comes from eggs: adult worms live in blood vessels where females release eggs, some passing out in feces or urine to continue the lifecycle, while others become trapped in body tissues causing immune reactions and progressive organ damage WHO.
There are two major forms of schistosomiasis—intestinal and urogenital—caused by five main species of blood fluke WHO. The species determines where the worms settle and what organs they affect.
Global Burden: The Numbers Behind the Crisis
The scale of schistosomiasis is staggering. WHO estimates that in 2024 globally 253.7 million people needed preventive chemotherapy for schistosomiasis, with coverage expanding to reach about 60% of children living in areas requiring treatment WHO.
But treatment coverage tells only part of the story. In 2024, 100.5 million people received preventive chemotherapy—83.1 million school-aged children and 17.4 million adults—corresponding to 39.6% global coverage, with school-aged children reaching 61.7% and adults just 14.6% GSA. Why such low adult coverage? Adults are often excluded from school-based treatment campaigns, leaving them vulnerable to chronic disease progression.
The geographic concentration is striking. It’s estimated that at least 93.9% of those requiring treatment for schistosomiasis live in Africa WHO, making this overwhelmingly an African health crisis. Sub-Saharan Africa bears nearly the entire disease burden, though pockets of transmission persist from Brazil to the Philippines. Research published in the New England Journal of Medicine analyzed nine national control programs and found that while some countries achieved control targets faster than WHO projected, high-intensity transmission settings struggled to meet 2020 and 2025 goals.
Schistosomiasis remains endemic in 79 countries, with transmission of Schistosoma haematobium newly confirmed in Cabo Verde GSA, expanding the disease map and underscoring persistent surveillance gaps.
According to CDC epidemiological data, different species dominate different regions: S. mansoni across sub-Saharan Africa and parts of South America; S. haematobium throughout Africa and Middle Eastern pockets; S. japonicum in China and the Philippines. Each species brings its own pattern of organ damage and complications.
Who faces the highest risk? Schistosomiasis mostly affects poor and rural communities, particularly agricultural and fishing populations, while women doing domestic chores in infested water such as washing clothes are also at risk and can develop female genital schistosomiasis WHO. Children are especially vulnerable due to frequent water contact during play.
Causes, Transmission & Risk Factors: The Snail Connection
Understanding schistosomiasis transmission requires understanding its complex lifecycle, which hinges entirely on one critical vector: freshwater snails.
Transmission occurs when people suffering from schistosomiasis contaminate freshwater sources with feces or urine containing parasite eggs, which hatch in water WHO. These hatched eggs release tiny swimming larvae called miracidia that seek out specific species of freshwater snails. The stages in the snail include two generations of sporocysts and the production of cercariae, which upon release from the snail swim and penetrate the skin of the human host CDC.
Here’s the troubling part: the Schistosoma parasite leaves the snail and enters the water where it can live for about 48 hours, with the parasite entering the skin of people who are in contact with unsafe water CDC. You can’t see these microscopic cercariae. The parasite can live in the water for only 48 hours without a mammalian host, but once a host has been found the worm enters blood vessels and develops into its adult phase over several weeks Wikipedia.
The biological mechanism is remarkably efficient. According to research in PLOS Neglected Tropical Diseases, each infected snail can release thousands of infective cercariae daily, and these larvae actively home in on human skin using chemical cues. This creates what scientists call a “nonlinear transmission pattern”—making elimination through drug treatment alone highly challenging.
What puts communities at risk? Inadequate hygiene and contact with infected water make children especially vulnerable to infection, while migration to urban areas and population movements are introducing the disease to new areas WHO.
The disease thrives where poverty intersects with water scarcity. Communities without access to clean water and proper sanitation turn to rivers, lakes, and ponds for daily needs—drinking, bathing, washing, even irrigation. Similar to challenges documented in our coverage of neglected tropical diseases, schistosomiasis disproportionately affects those already marginalized by economic inequality.
Dam construction and irrigation projects can inadvertently worsen transmission. Studies referenced in WHO literature show that large-scale water development projects often create ideal snail habitats, expanding transmission zones into previously unaffected areas.
Signs, Symptoms & Health Impacts: What WHO Identifies
Many people are asymptomatic and have subclinical disease during both acute and chronic stages of infection, with the incubation period for patients with acute schistosomiasis usually 14-84 days CDC.
WHO identifies several disease phases. The acute phase, known as Katayama fever, is a systemic hypersensitivity reaction that may occur weeks after initial infection, especially by S. mansoni and S. japonicum, with manifestations including fever, cough, abdominal pain, diarrhea, hepatosplenomegaly, and eosinophilia CDC.
For chronic infections, symptoms depend on which organs the eggs damage. S. mansoni and S. japonicum eggs most commonly lodge in blood vessels of the liver or intestine, while S. haematobium eggs tend to lodge in the urinary tract causing damage that can lead to dysuria and hematuria CDC.
According to Cleveland Clinic’s clinical overview, intestinal schistosomiasis causes abdominal pain, diarrhea, and bloody stool, while urogenital forms produce blood in urine—sometimes the only visible sign of infection.
In children, schistosomiasis can cause anemia, stunting and a reduced ability to learn, although the effects are usually reversible with treatment WHO. This mirrors patterns seen in other parasitic infections affecting adolescent health and development.
Chronic schistosomiasis may affect people’s ability to work and in some cases can result in death, with difficulty estimating deaths due to hidden pathologies such as liver and kidney failure, bladder cancer and ectopic pregnancies due to female genital schistosomiasis WHO.
Female genital schistosomiasis (FGS) deserves special attention. In women, urogenital schistosomiasis may present with genital lesions, vaginal bleeding, pain during sexual intercourse and nodules in the vulva WHO. Research published in BMC Public Health found that healthcare workers in endemic areas often misdiagnose FGS as sexually transmitted infections, delaying proper treatment. If left untreated, FGS leads to chronic inflammation, open lesions, scarring throughout the female genital tract, and severe reproductive health complications including infertility, ectopic pregnancy, miscarriage, and poor birth outcomes Eliminateschisto.
FGS has also been associated with an increased vulnerability to HIV and HPV infection, and cervical cancer due to physical and immunological changes caused by schistosomiasis Eliminateschisto. WHO now recognizes the intersection between schistosomiasis and HIV as a critical public health concern.
Treatment & Health Response: Current Approaches and Access Gaps
WHO reports that current treatment focuses on a single drug: praziquantel. Praziquantel is the recommended treatment against all forms of schistosomiasis and is effective, safe and low-cost, though re-infection may occur after treatment WHO.
Here’s the treatment reality: the risk of developing severe disease is diminished and even reversed when treatment is initiated and repeated in childhood WHO. A single dose kills adult worms. But there’s a catch—praziquantel doesn’t prevent re-infection in endemic areas where water contact continues.
A major limitation to schistosomiasis control has been the limited availability of praziquantel, particularly for the treatment of adults WHO. School-based treatment programs reach children more easily than adults, creating a coverage gap. Three countries reported treating 403,986 preschool-aged children with praziquantel in 2024: The Gambia, Tanzania-Zanzibar, and the Philippines GSA—but most endemic countries don’t treat this young age group at all.
Regional differences in treatment access are stark. In the African Region, 82.6 million school-aged children and 15.6 million adults were treated with coverage of 41.4% overall, while no preventive chemotherapy was reported in Brazil and Venezuela despite need GSA. The Eastern Mediterranean saw similar gaps: no treatment reported in Somalia, Sudan, or Yemen.
According to WHO’s treatment guidelines, mass drug administration targets entire at-risk communities, but implementation varies wildly by country capacity and funding.
For female genital schistosomiasis, treatment limitations are particularly concerning. Research from Drugs for Neglected Diseases initiative indicates that praziquantel kills adult worms but doesn’t relieve painful symptoms caused by inflammatory reactions to eggs already deposited in tissue. New combination treatments are needed specifically for FGS.
The treatment infrastructure gap extends beyond drug availability. Many health facilities in endemic areas lack diagnostic equipment for confirming schistosomiasis or assessing treatment effectiveness. Diagnosis typically requires microscopic examination of urine or stool for eggs—a lab capacity not universally available in rural clinics.
Prevention & WHO Strategies: Public Health Policy Framework
The control of schistosomiasis is based on large-scale treatment of at-risk population groups, access to safe water, improved sanitation, hygiene education, behavior change and the One Health approach to control snail intermediate hosts and zoonotic transmission WHO.
WHO’s multipronged strategy goes beyond just pills. Schistosomiasis control focuses on reducing disease through periodic large-scale population treatment with praziquantel, while a more comprehensive approach including ensuring access to safe drinking water, adequate sanitation, behavior change interventions, veterinary public health and snail control can also reduce transmission WHO.
What does comprehensive prevention actually look like? According to WHO’s NTD roadmap 2021-2030, interventions must address multiple transmission points:
Water and sanitation infrastructure: Providing safe water sources and proper toilets prevents contamination of water bodies with human waste containing parasite eggs. This breaks the transmission cycle at its source.
Snail control: Environmental management and targeted molluscicides reduce snail populations in transmission sites. Some programs restore natural predators—like freshwater prawns—that eat snails, providing biological control.
Health education: Teaching communities about transmission risks, especially for children and women who have high water contact through daily activities. Behavioral changes around where and how people use water can dramatically reduce infection rates.
Veterinary public health: Hybrids of human and animal schistosomes have been reported in humans in many sub-Saharan African countries, with some hybrids having the potential to transmit schistosomiasis WHO. Treating infected livestock helps control zoonotic transmission.
WHO guidance emphasizes verification after five years of at least 75% effective coverage and provides new manuals for analyzing routine health facility data to support impact tracking and strategy revision WHO. Countries must maintain high treatment coverage for years before attempting elimination verification.
China’s experience offers lessons. The country shifted strategies three times since the 1950s—from transmission control to morbidity control to an integrated approach combining chemotherapy, snail control, improved sanitation, and replacing bovine agricultural labor with machinery. This integrated strategy proved highly effective in reducing both human and snail infection rates.
WHO’s Global Efforts: Progress, Targets & Partnerships
The 2030 targets for schistosomiasis set out in the Roadmap for neglected tropical diseases are to eliminate the disease as a public health problem in all endemic countries and to eliminate transmission in some WHO.
Recent WHO news provides both hope and concern. Egypt has submitted its dossier for elimination of schistosomiasis as a public health problem, with a WHO review committee convened GSA (as of December 2024). This would mark a major milestone—Egypt once had one of the world’s highest schistosomiasis burdens.
Multiple countries are preparing verification dossiers after achieving at least ten years without locally-acquired cases, including Mauritius in Africa and nine countries/territories in the Americas such as Puerto Rico, Suriname, and the Dominican Republic GSA. These represent genuine elimination successes, though they’re generally smaller countries or island nations where controlling freshwater transmission proved more feasible.
But setbacks complicate the picture. Transmission of Schistosoma haematobium was newly confirmed in Cabo Verde, a country not previously considered endemic GSA, expanding the disease map and reminding us that schistosomiasis can establish in new areas when conditions allow. A 2013 outbreak in Corsica, France, linked to hybrid animal-human schistosomes, demonstrated that even non-endemic regions aren’t immune.
The World Health Assembly has set specific targets. Resolution WHA65.21 calls for reaching at least 75% of school-aged children at risk of morbidity from schistosomiasis. Data for 2024 show that 61.7% of school-aged children requiring preventive chemotherapy were treated WHO—close, but not yet meeting the target.
How does this compare to initial WHO goals? Research in the New England Journal of Medicine found that WHO set goals for controlling schistosomiasis morbidity by 2020 and achieving elimination as a public health problem by 2025 in all endemic countries. As we entered 2025, many high-burden countries remained far from these targets.
Partnerships drive progress. The Schistosomiasis Control Initiative, pharmaceutical donations from Merck KGaA (which provides praziquantel), the END Fund, and country-level ministries of health collaborate on treatment campaigns. In January 2026, WHO established the Schistosomiasis Elimination Review Group comprising approximately 18 multidisciplinary members to provide independent evaluation on whether countries meet elimination criteria WHO.
What’s working? Countries that combine mass drug administration with water/sanitation improvements and community engagement see faster progress than those relying on treatment alone. What’s not working? Fifteen countries requiring preventive chemotherapy for schistosomiasis did not carry out mass drug administration in 2024—ten in Africa, two in the Americas, and three in the Eastern Mediterranean GSA. Political instability, funding gaps, and lack of health infrastructure all contribute to these failures.
The hard truth: elimination in high-transmission settings requires sustained commitment over decades. Mathematical modeling research suggests that in areas with intense snail-human transmission, local elimination by implementation of mass drug administration alone is highly unlikely even over a multi-decade period, due to efficiency of human-to-snail transmission being much higher than predicted by standard models PubMed Central. This means water and sanitation infrastructure isn’t just helpful—it’s essential for elimination.
Does the global community have the political will to fund comprehensive control? That remains the critical question as we approach 2030 targets.
Related Health Context
The intersection of schistosomiasis with other health challenges creates compounded risks. The disease contributes to anemia in children and pregnant women through chronic blood loss and nutritional impacts. As a neglected tropical disease, it shares common risk factors with other waterborne and poverty-associated illnesses affecting vulnerable populations.
The link between schistosomiasis and HIV transmission represents an emerging public health concern that demands integrated sexual and reproductive health interventions. WHO and UNAIDS have called for schistosomiasis treatment to be included in HIV prevention programs in co-endemic areas.
For those interested in the broader historical context of disease control efforts and public health milestones, our world history section explores how societies have confronted epidemics across centuries.
The challenges of diagnosing and treating schistosomiasis in marginalized communities echo themes explored during Global Accessibility Awareness Day, where equity in health access remains a central concern.
Frequently Asked Questions
No. According to WHO, schistosomiasis requires freshwater snails to complete its lifecycle. The parasite can’t transmit directly between humans. Infection only occurs through contact with contaminated water containing cercariae released from infected snails. Even intimate contact with an infected person won’t spread the disease.
WHO reports that adult schistosomes can live an average of three to five years in human blood vessels, though eggs can survive in tissues for more than 30 years after infection. Without treatment, worms continue producing eggs throughout their lifespan, causing progressive organ damage and maintaining the transmission cycle in communities.
Currently no vaccine exists for schistosomiasis. WHO emphasizes that prevention relies on avoiding contaminated water, ensuring access to safe water and sanitation, and annual or biannual mass drug administration with praziquantel in endemic areas. Several vaccine candidates are in research phases, but none have reached widespread use.
WHO data shows that 93.9% of people requiring treatment live in Africa because the continent has the right combination of factors: specific freshwater snail species that host the parasite, widespread poverty limiting access to clean water and sanitation, and agricultural/fishing economies requiring extensive water contact. Climate and ecology support year-round transmission in many African regions.
Yes. WHO clarifies that praziquantel treatment kills adult worms but doesn’t prevent re-infection. People living in endemic areas who continue water contact often get infected repeatedly. This is why control programs provide treatment annually or every two years rather than just once. Repeated childhood treatment prevents severe disease even if re-infection occurs.
Sources
- World Health Organization. (2024). Schistosomiasis Fact Sheet. Retrieved from https://www.who.int/news-room/fact-sheets/detail/schistosomiasis
- Centers for Disease Control and Prevention. (2024). DPDx – Schistosomiasis Infection. Retrieved from https://www.cdc.gov/dpdx/schistosomiasis/index.html
- Archer, J., et al. (2019). Schistosomiasis – Assessing Progress toward the 2020 and 2025 Global Goals. New England Journal of Medicine, 381, 2519-2528. https://www.nejm.org/doi/full/10.1056/NEJMoa1812165
- Global Schistosomiasis Alliance. (2024). Progress under pressure: Countries advance dossiers as schistosomiasis landscape evolves. Retrieved from https://www.eliminateschisto.org/news-events/news/progress-under-pressure-countries-advance-dossiers-as-schistosomiasis-landscape
DISCLAIMER
This article adapts publicly available information from WHO’s Schistosomiasis page. This content is for informational and educational purposes only and does not constitute medical advice. ObserverVoice.com is a news and information platform—not a healthcare provider.
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