Schistosomiasis

What is Schistosomiasis?

Schistosomiasis, also known as bilharzia, is a neglected tropical disease caused by parasitic worms that depend on freshwater snails for part of their life cycle. Infection typically occurs when people come into contact with contaminated freshwater, making it closely linked to daily activities such as bathing, fishing, or washing in affected areas.

The disease remains a major global health concern, with an estimated 253.7 million people requiring preventive treatment in 2024. Transmission has been reported across 79 countries, with the overwhelming majority of those affected, about 93.9%, living in Africa. Recognized as the second most impactful parasitic disease after malaria, schistosomiasis continues to disproportionately affect vulnerable communities with limited access to safe water and sanitation.

Micrograph of human parasite Schistosoma mansonii which causes tropical diseases schistosomiasis, transverse section through male and female parasites in copulation, light microscopy, X120

What are the causes of Schistosomiasis?

Schistosomiasis is caused by parasitic worms of the genus Schistosoma, with the main species affecting humans including S. mansoni, S. haematobium, and S. japonicum. Infection occurs when the infectious larval stage (cercariae) is released from freshwater snails into contaminated water and penetrates human skin upon contact.

Once inside the body, the parasites mature into adult worms within blood vessels, where they reproduce and produce eggs. Some of these eggs are excreted through urine or stool, continuing the transmission cycle when they reach freshwater environments and infect snails again. This life cycle closely links the disease to everyday exposure to unsafe water sources in endemic regions.

Symptoms of Schistosomiasis

Schistosomiasis often presents with minimal or no symptoms in the early stages, though some individuals may develop an initial skin reaction shortly after exposure.

Early-phase symptoms (first days):

Itchy, bumpy skin rash or “swimmer’s itch”
Prickling or stinging sensation at the site of water contact

Acute phase (1–2 months post-infection):

Fever and chills
Headache
Muscle and joint pain
Fatigue
Cough
Abdominal pain
Diarrhoea (sometimes blood-stained)
Blood in urine
Genital symptoms such as vaginal pain, sores, bleeding, or discomfort during sex

Chronic or repeated infection effects (especially in children):

Anaemia (low red blood cell count)
Malnutrition
Learning or cognitive difficulties

Rare severe neurological complications:

Seizures
Severe headaches
Vision disturbances
Difficulty walking or coordination problems

Overall, disease progression ranges from mild or silent infection to significant systemic and neurological complications, particularly with repeated exposure or prolonged infection.

Diagnostics and Treatment of Schistosomiasis

Schistosomiasis is diagnosed primarily by identifying parasite eggs in urine or stool samples, with additional support from antigen or antibody detection in blood or urine. Diagnostic methods vary depending on the infection site and transmission setting.

Key diagnostic approaches:

Urine filtration techniques (nylon, paper, or polycarbonate filters) for urogenital infection
Reagent strip tests to detect microscopic blood in urine, especially in children with S. haematobium
Kato-Katz technique for detecting eggs in stool samples in intestinal infection
Circulating cathodic antigen (CCA) test in S. mansoni endemic areas
Serological or immunological tests in low-transmission or non-endemic regions to assess exposure

Treatment:

Praziquantel is the standard therapy and is effective against adult worms
It does not prevent infection immediately after exposure and is not suitable as a post-exposure preventive measure
No vaccine currently exists for schistosomiasis

Overall, diagnosis depends on both direct parasite detection and supportive immunological evidence, while treatment remains effective but time-dependent, targeting established adult infections rather than early exposure.

Recent Updates

Schistosomiasis control efforts in 2024 show both progress and ongoing gaps in global coverage. Overall, 39.6% of people requiring preventive treatment were reached worldwide, including 61.7% of school-aged children eligible for preventive chemotherapy, indicating better targeting of high-risk groups but incomplete global access.

Over the past four decades, sustained control programmes have successfully reduced disease burden in several countries, including Brazil, China, Egypt, and Morocco, as well as parts of the Caribbean and the Middle East. In sub-Saharan Africa, where most at-risk populations live, expanded treatment campaigns over the past decade have contributed to an estimated 60% reduction in prevalence among school-aged children, reflecting meaningful but uneven progress in global control efforts.