Overview
Schistosomiasis, also called bilharzia or snail fever, is an infection caused by parasitic schistosomes, a group of blood-dwelling flatworms. People acquire the infection through contact with contaminated fresh water where specific freshwater snails release larval stages of the parasite. Infection ranges from mild and self-limited to chronic and disabling, depending on the species involved, intensity of exposure, and access to diagnosis and care.
Life cycle and characteristics
Schistosomes have a complex lifecycle that requires both a human (or other mammal) host and freshwater snails. Free-swimming larvae released from snails penetrate human skin during activities such as bathing, swimming, fishing or wading. Inside the body the parasites mature in the bloodstream and the adult worms lodge in veins near the intestines or bladder, producing eggs that provoke inflammation and tissue damage. Eggs pass out of the body in feces or urine, continuing the cycle if they reach suitable snail hosts.
Signs, complications and notable findings
Early infection may cause non-specific symptoms; later effects are mainly due to the immune response to eggs trapped in tissues. Common manifestations include:
- Abdominal pain, especially with intestinal forms.
- Diarrhea and bloody stools in intestinal infections.
- Urinary symptoms including frequency, pain and visible blood in the urine with urinary schistosomiasis.
Long-standing untreated infection can lead to serious complications such as liver enlargement and fibrosis, portal hypertension, impaired growth and cognitive effects in children, and genitourinary damage. Chronic disease has been associated with increased risk of bladder cancer and reproductive problems including reduced fertility and infertility; severe cases may contribute to renal impairment or kidney failure. In children, repeated infection is linked to anemia, poor growth and learning difficulty.
Diagnosis and treatment
Diagnosis most often relies on finding parasite eggs in stool or urine specimens; serologic tests and antigen detection can aid diagnosis when egg detection is difficult. Imaging and blood tests may assess organ damage. The antiparasitic drug praziquantel is the principal treatment and is effective against adult worms; it is widely used in individual therapy and mass drug administration programs. The World Health Organization (WHO) recommends targeted treatment in endemic areas to reduce morbidity and transmission.
Prevention, control and public health importance
Control strategies combine chemotherapy, safe water supply, sanitation, health education and environmental measures that reduce snail populations. Simple behavior changes—avoiding contact with known contaminated water—can lower risk, but lasting control usually requires improved water and sanitation infrastructure and routine treatment campaigns in high-prevalence communities. Schistosomiasis remains a major neglected tropical disease with hundreds of millions at risk across parts of Africa, Asia and the Americas; it contributes to poverty by impairing health, education and productivity.
Distinctions and additional notes
Several Schistosoma species infect humans; the most common are S. haematobium (mainly urinary disease) and S. mansoni and S. japonicum (mainly intestinal and hepatic disease). Geographic distribution, clinical features and control priorities vary by species and local ecology. Effective control requires integrating clinical care, surveillance and environmental management tailored to local transmission patterns.