Schistosomiase

Schistosomiasis is an acute and chronic parasitic disease caused by blood flukes (trematode worms) of the genus Schistosoma ^[1]. The main clinical forms are intestinal and urogenital disease, associated with different Schistosoma species and with adult worms residing in blood vessels draining the intestines or urinary tract ^[1][2]. Pathological effects are largely produced by trapped eggs and host immune reactions, although some eggs are excreted to continue the lifecycle ^[1][2]. The condition is a disease of poverty linked to freshwater exposure in communities lacking safe water and adequate sanitation ^[2].

In chronic infection, adult worms lay eggs that can become trapped in tissues and trigger inflammatory reactions, including eosinophilic responses when eggs lodge in organs such as the liver, spleen, lungs, or brain ^[4]. Many infections are mildly symptomatic, while anemia and malnutrition are common in endemic settings, and long-term manifestations vary by species and the migration sites of adult worms ^[4]. Blood in the urine has been a historically prominent symptom in endemic settings ^[4]. Chronic disease may also be associated with pulmonary hypertension as a serious complication in some populations ^[5].

Schistosomiasis is one of the most prevalent parasitic diseases globally, endemic in more than 70 countries with over 200 million people infected ^[5]. Recent estimates indicate that at least 253.7 million people required preventive treatment in 2024, while transmission has been reported from 79 countries ^[1]. A separate assessment places the affected population at more than 250 million people across 78 countries, with approximately 800 million worldwide at risk and an estimated 280,000–500,000 deaths annually ^[3]. An estimated 93.9% of those requiring treatment live in Africa, and preventive chemotherapy is currently required in 50 endemic countries with moderate-to-high transmission ^[1]. Transmission of Schistosoma haematobium has recently been confirmed in Cabo Verde, which was not previously considered endemic ^[1].

Schistosomiasis is spread by contact with fresh water contaminated with parasites released from infected freshwater snails; larval forms of the parasite penetrate the skin during contact with infested water ^[4][1]. Transmission occurs when infected people contaminate freshwater sources with faeces or urine containing parasite eggs, which then hatch in water ^[1]. Inside the body, larvae develop into adult schistosomes that reside in blood vessels, where females release eggs; some eggs exit via faeces or urine to continue the lifecycle, while others become trapped in tissues, driving immune-mediated organ damage ^[1]. The disease is especially common where contaminated water is used for daily activities; children in developing countries are frequently exposed through play in infested water, and women typically face greater exposure through domestic chores involving contact with such water ^[4]. Hybrids of human and animal schistosomes (such as S. haematobium–S. bovis and S. haematobium–S. mattheei) have been reported in humans across many sub-Saharan African countries, with confirmed zoonotic and hybrid transmission capacity demonstrated by the 2013 outbreak in Corsica, France ^[1].

High-risk groups include people living in endemic areas who contact infested freshwater, especially agricultural and fishing populations ^[1]. Poor and rural communities without access to safe drinking water and adequate sanitation bear the greatest burden, and women performing domestic chores in infested water, such as washing clothes, are also at risk ^[1]. Preventive treatment is targeted to high-risk populations living in areas where the disease is common, and large-scale treatment is directed at at-risk groups ^[4][1]. Almost 800 million people worldwide are estimated to be at risk for schistosomiasis ^[3].

Prevention relies on large-scale treatment of at-risk population groups, access to safe water, improved sanitation, hygiene education, and behaviour change ^[1]. Preventive treatment programmes are used for high-risk populations living in areas where the disease is common ^[4]. Snail intermediate hosts can be targeted through One Health approaches and, historically, molluscicides, though molluscicide campaigns were costly and often reduced rather than eliminated snail populations ^[4][1]. Countries and the World Health Organization are promoting elimination efforts, and environmental changes such as urbanization, pollution, and destruction of snail habitat have reduced exposure and new infections in some cases ^[4].

In surveillance and public-health monitoring, screening indicators can support case finding: urine dipstick testing for hematuria has been used to screen communities for S. haematobium, while stool blood testing may identify potential S. mansoni or S. japonicum infection ^[4]. Blood eosinophilia may be used as a supportive signal in travelers or migrants from endemic regions, and liver-function testing may guide further investigation when hepatosplenic disease is suspected ^[4]. These markers support screening and monitoring, and follow-up investigation may be guided by species-specific pathways and liver-function testing when indicated ^[4].

1. 1 World Health Organization. Schistosomiasis [Internet]. cited 3 Sept 2026. Available from: https://www.who.int/news-room/fact-sheets/detail/schistosomiasis
2. 2 World Health Organization. Schistosomiasis (Bilharzia) [Internet]. cited 2 Sept 2026. Available from: https://www.who.int/health-topics/schistosomiasis
3. 3 LoVerde PT et al. Schistosomiasis. Adv Exp Med Biol. 2024. PMID: 39008264. doi: 10.1007/978-3-031-60121-7_3. PubMed: https://pubmed.ncbi.nlm.nih.gov/39008264/
4. 4 Wikipedia contributors. Schistosomiasis - Wikipedia [Internet]. Wikipedia. cited 3 Sept 2026. Available from: https://en.wikipedia.org/wiki/Schistosomiasis
5. 5 Şen N et al. [Schistosomiasis and pulmonary hypertension]. Tuberk Toraks. 2017 Sep. PMID: 29135402. doi: 10.5578/tt.53798. PubMed: https://pubmed.ncbi.nlm.nih.gov/29135402/