Schistosomiasis

Schistosomiasis, also known as bilharzia or snail fever, is a neglected tropical disease caused by parasitic flatworms (blood flukes) of the genus Schistosoma. The disease manifests in two major forms: urogenital schistosomiasis caused primarily by Schistosoma haematobium, and intestinal schistosomiasis caused by S. mansoni, S. japonicum, S. mekongi, S. guineensis, and S. intercalatum. The microscopic adult worms reside in the blood vessels draining the urinary tract and intestines, where females release eggs that either pass out of the body or become trapped in tissues, provoking immune-mediated damage.

Clinical manifestations arise primarily from the host immune response to schistosome eggs deposited in tissues. Acute infection may present as cercarial dermatitis (swimmer's itch) within hours of water contact, followed by Katayama fever 2-8 weeks later, characterized by fever, myalgia, cough, and bloody diarrhea. Chronic intestinal schistosomiasis causes abdominal pain, diarrhea, and bloody stool, with liver enlargement, splenomegaly, and ascites in advanced cases. Urogenital schistosomiasis classically presents with hematuria, potentially progressing to kidney damage, bladder fibrosis, and increased bladder cancer risk. Children may experience impaired growth and cognitive development, while adults may develop infertility or portal hypertension.

Schistosomiasis affects nearly 240 million people worldwide, with an estimated 253.7 million requiring preventive treatment in 2024. Transmission has been documented across 79 countries, though preventive chemotherapy is required in 50 endemic countries with moderate-to-high transmission. Approximately 93.9% of those requiring treatment reside in Africa, with the disease concentrated in poor rural communities lacking safe drinking water and adequate sanitation. Agricultural and fishing populations face elevated exposure risk, and women performing domestic water-based activities such as laundry are particularly vulnerable. Hybrid schistosome strains combining human and animal parasites have been identified in multiple sub-Saharan African countries, with documented zoonotic transmission events.

Human infection occurs when larval forms (cercariae) released by freshwater snails penetrate the skin during contact with infested fresh water. The transmission cycle is maintained when infected individuals contaminate water sources with feces or urine containing parasite eggs, which hatch in water to release miracidia that infect specific snail intermediate hosts. The snails then shed cercariae into the water, completing the lifecycle. Transmission is therefore dependent on both the presence of infected snails and human water contact behaviors in communities with inadequate sanitation.

Source-backed detail on specific high-risk groups is not yet available beyond the general characterization of poor, rural communities in tropical and subtropical areas with inadequate water and sanitation. Agricultural workers, fishing populations, and women engaged in domestic water-based activities are mentioned as particularly exposed, though quantitative risk stratification data is not provided in the source material.

The WHO control strategy integrates large-scale preventive chemotherapy with praziquantel for at-risk populations, repeated over multiple years to reduce morbidity and interrupt transmission. Complementary interventions include expanding access to safe drinking water, improving sanitation infrastructure, implementing hygiene education, and promoting behavior change to reduce water contact. Snail intermediate host control through environmental modification and the One Health approach addresses zoonotic transmission risks. Praziquantel has been safely co-administered with albendazole and ivermectin for integrated neglected tropical disease control in endemic areas.

Surveillance for schistosomiasis relies on parasitological detection of eggs in stool (intestinal form) or urine (urogenital form) specimens, with the Kato-Katz technique and filtration methods serving as standard diagnostic approaches. Antibody and antigen detection in blood or urine provides additional diagnostic evidence. Sentinel group monitoring guides community-level treatment decisions in highly endemic areas. The recent confirmation of S. haematobium transmission in Cabo Verde, previously considered non-endemic, illustrates the importance of vigilance for emerging transmission in regions with suitable snail habitats and water contact patterns.

1. 1 WHO Health Topics. Schistosomiasis (Bilharzia).
2. 2 WHO Fact Sheet. Schistosomiasis.
3. 3 WHO Q&A. News.
4. 4 Wikidata. schistosomiasis.
5. 5 Wikipedia. Schistosomiasis - Wikipedia.

ICD-10

B65

ICD-11

1F86

Total cases

85K

Total deaths

9

Peak month

2015-11

Coverage

1 reporting countries · 2010-01-01 → 2026-04-01