Schistosomiasis, also known as bilharzia, is a chronic parasitic disease caused by blood flukes of the genus Schistosoma. It is one of the neglected tropical diseases (NTDs) with major global health consequences, leading to chronic illness, organ damage, and socioeconomic burdens in endemic regions. Transmission occurs through freshwater containing the larval stage (cercariae), which penetrate human skin, mature, and produce eggs that cause inflammation and fibrosis. 

Despite being preventable and treatable, schistosomiasis remains widespread in Africa, Asia, and South America, affecting over 200 million people. The chronic nature of the disease means individuals often live with ongoing symptoms, reducing workforce productivity and contributing to poverty. Understanding its biology, transmission, and prevention is critical for healthcare providers and public health workers. 

Schistosomiasis is caused by trematode worms of the genus Schistosoma, which inhabit the human venous system and lead to chronic organ damage. Unlike many parasitic infections, schistosomiasis requires both freshwater snails as intermediate hosts and humans as definitive hosts. 

The type of schistosomiasis depends on the parasite species involved. Different species tend to target different organs, which explains the variety of symptoms seen in patients. Recognizing the type is important for diagnosis, treatment, and understanding potential complications. 

Intestinal schistosomiasis: 

• Caused by Schistosoma mansoni, S. japonicum, S. mekongi, and S. intercalatum. 

• Primarily affects the intestines and liver. 

Urogenital schistosomiasis: 

• Caused by Schistosoma haematobium. 

• Primarily affects the urinary tract and genital organs. 

Schistosomiasis remains endemic in many low- and middle-income countries. 

• Endemic in 74 countries, mainly in sub-Saharan Africa. 

• About 240 million people are infected worldwide, with over 700 million at risk. 

• School-aged children and young adults are most affected due to frequent water contact. 

• Transmission occurs in Africa, the Middle East, South America (Brazil, Venezuela), and Southeast Asia (Philippines, parts of China). 

Climate change, migration, and water development projects can alter transmission patterns by expanding snail habitats and human exposure. 

Understanding the life cycle is essential for prevention and control. 

• Eggs are passed in urine (S. haematobium) or stool (S. mansoni, S. japonicum). 

• In freshwater, eggs hatch into miracidia, which infect specific freshwater snails. 

• Inside the snail, miracidia develop into sporocysts, producing cercariae. 

• Cercariae are released into water and actively seek human hosts. 

• Cercariae penetrate human skin, lose their tails, and become schistosomulae. 

• Schistosomulae migrate through the bloodstream to the liver to mature. 

• Adult worms migrate to mesenteric (intestinal) or vesical (bladder) venous plexuses, depending on species. 

• Adult worms produce eggs, which either exit the body or become trapped in tissues, causing inflammation and granulomas. 

The primary damage in schistosomiasis comes from the body’s immune reaction to parasite eggs trapped in tissues. Over time, this ongoing response causes inflammation and scarring that can disrupt the normal function of affected organs. These changes are responsible for many of the long-term complications seen in chronic disease, such as liver damage, bladder problems, and increased risk of cancer. 

• The immune response causes chronic inflammation. 

• Fibrosis develops in affected organs. 

• Organ-specific complications result from prolonged damage. 

Acute infection (Katayama fever) occurs due to the immune system’s reaction to migrating schistosomula and new egg deposition. 

People acquire schistosomiasis through direct skin contact with contaminated freshwater. The larvae (cercariae) penetrate the skin while swimming, bathing, or working in infected water. 

• After entering, cercariae transform into schistosomula and migrate to the liver. 

• Adult worms live in blood vessels around the intestines or bladder, depending on the species. 

• Eggs may pass into stool or urine, continuing the life cycle, or become trapped in organs, causing inflammation. 

• Drinking contaminated water does not transmit schistosomiasis—only skin contact does. 

Children, farmers, and fishermen in endemic regions are at highest risk. 

The symptoms of schistosomiasis vary depending on whether the infection is acute or chronic. In the early stages, patients may show signs related to the body’s immune response, while chronic disease is linked to long-term egg deposition in specific organs. Understanding these patterns helps clinicians recognize the disease and provide timely treatment. 

Acute schistosomiasis (Katayama syndrome): 

• Develops weeks after initial infection. 

• Symptoms include fever, chills, muscle pain, cough, hives, and high eosinophil counts. 

• More common with S. japonicum and in travelers. 

Chronic schistosomiasis: 

Intestinal disease: 

• Diarrhea, sometimes bloody. 

• Abdominal pain. 

• Enlarged liver and spleen. 

• Portal hypertension and esophageal varices. 

Hepatosplenic disease: 

• Associated with S. mansoni and S. japonicum. 

• Periportal fibrosis leading to portal hypertension, with preserved liver function early on. 

Urogenital disease: 

• Blood in urine (terminal hematuria). 

• Painful urination and urinary frequency. 

• Hydronephrosis and bladder wall calcification. 

• Increased risk of bladder cancer (squamous cell carcinoma). 

Genital disease: 

• Infertility and genital lesions. 

• Increased risk of HIV transmission. 

Diagnosis uses parasitological, serological, and imaging methods. Clinicians often combine these approaches to improve accuracy, since no single test is perfect for every case. The choice of method depends on the intensity of infection, the available resources, and whether the patient is in an endemic or non-endemic setting. 

• Microscopy: Egg identification in urine or stool. 

• Serology: Detects antibodies, useful in travelers and low-burden cases. 

• Antigen detection: Measures circulating worm antigens in blood or urine. 

• Imaging: Ultrasound, CT, or MRI detect organ complications. 

• Blood tests: Eosinophilia is often present in acute infection. 

New point-of-care diagnostic tests are being developed for use in resource-limited areas. 

Schistosomiasis can lead to a wide range of complications if left untreated, many of which are severe and long-lasting. These complications arise mainly from the immune system’s reaction to eggs trapped in tissues, leading to chronic inflammation and fibrosis. Understanding the complications is important for clinicians, as they can affect multiple organ systems and significantly reduce quality of life. 

• Portal hypertension and variceal bleeding. 

• Enlarged liver and spleen. 

• Chronic diarrhea and malnutrition. 

• Bladder cancer. 

• Hydronephrosis and kidney failure. 

• Pulmonary hypertension. 

• Spinal cord inflammation (transverse myelitis). 

• Increased risk of HIV and other infections. 

Treatment is aimed at eliminating the parasites, reducing symptoms, and preventing long-term complications. Early therapy helps limit organ damage and reduces transmission in communities. Understanding available drugs and supportive care is essential for both clinicians and public health programs. 

Praziquantel is the mainstay of treatment and is effective against all species. 

Dose: 

• S. mansoni, S. haematobium, S. intercalatum: 40 mg/kg once. 

• S. japonicum, S. mekongi: 60 mg/kg in two divided doses. 

• Alternative: Oxamniquine for S. mansoni in some regions. 

Supportive care: Management of complications such as portal hypertension, iron supplementation for anemia, and surgery for advanced urological disease. 

Re-treatment is often necessary in high-risk areas. Surveillance programs monitor drug effectiveness and potential resistance. 

Prevention strategies are designed to break the cycle of transmission and protect highrisk groups. Combining medical treatment with education, sanitation improvements, and environmental management provides the most effective results. These approaches must involve both local communities and international health organizations for sustainable success. 

Prevention requires combined strategies: 

• Mass drug administration: Routine praziquantel distribution to schoolchildren and at-risk adults. 

• Health education: Avoidance of contact with contaminated water and safe water practices. 

• Sanitation: Improved water supply and waste disposal. 

• Snail control: Use of molluscicides and environmental management to reduce snail habitats. 

Community education and behavior change are essential. School-based programs combining education and treatment have proven effective. 

Chronic schistosomiasis affects quality of life. 

• Chronic pain and discomfort. 

• Fatigue and anemia. 

• Social stigma in affected communities. 

• Anxiety about cancer and long-term organ damage. 

Regular monitoring, early treatment, and complication management improve patient outcomes. 

Schistosomiasis remains a major global health challenge, particularly in resource-limited areas. Early diagnosis and prompt praziquantel treatment prevent complications, but long-term success requires sanitation improvements, education, and global collaboration. With sustained international effort, research, and community engagement, elimination is possible. 

1. World Health Organization (WHO). Schistosomiasis. Available at: https://www.who.int/health-topics/schistosomiasis 

2. Colley DG, Bustinduy AL, Secor WE, King CH. Human schistosomiasis. Lancet. 2014;383(9936):2253-64. 

3. Gryseels B, Polman K, Clerinx J, Kestens L. Human schistosomiasis. Lancet. 2006;368(9541):1106-18. 

4. Centers for Disease Control and Prevention (CDC). Schistosomiasis. Available at: https://www.cdc.gov/parasites/schistosomiasis/ 

5. World Health Organization. Helminth control in school-age children: a guide for managers of control programmes. 2nd ed. Geneva: WHO; 2011.