Bilharzia: The Nile Parasite, What It Does Inside You and How to Treat It

What is bilharzia and how does it live in your body?

Bilharzia, also known as schistosomiasis, is a parasitic disease caused by microscopic flatworms of the genus Schistosoma. Part of the parasite's life cycle takes place inside a small freshwater snail that lives in slow-moving or still freshwater. The snail releases free-swimming larvae called cercariae into the water, and these larvae can penetrate human skin on direct contact.

Once through the skin, the larvae transform into a different stage, migrate through the bloodstream to the lungs and then the liver, and mature into adult worms that pair up. The adults settle in the blood vessels surrounding the bladder or the intestines depending on the species, and they can live there for years, continuously laying eggs. It is the eggs that cause the inflammation and damage, because they trigger intense immune reactions in the surrounding tissue.

The two species most relevant to our region are S. haematobium, which affects the bladder and urinary tract and is prevalent in Egypt, Sudan and North Africa, and S. mansoni, which affects the liver and intestines and is found in parts of sub-Saharan Africa and Sudan. Both spread through wading or swimming in contaminated water, not through drinking or breathing.

Where is bilharzia found in our region?

Egypt has one of the longest recorded histories of bilharzia of any country in the world, with evidence of the parasite found in ancient Egyptian mummies. A 2013 review published in the Journal of Advanced Research documented the significant decline in prevalence since the 1970s due to systematic control campaigns, but the disease persists in Nile Delta villages and rural farming communities that rely on irrigation canals.

A study published in 2020 in Infectious Diseases of Poverty found that some areas of the Nile Delta still record meaningful prevalence today. In Sudan, a 2026 study in Parasitology Research reported that the prevalence of urogenital schistosomiasis among school-age children in the Gezira irrigated region remained strikingly high, reinforcing the close link between agricultural irrigation and parasite transmission.

The risk is tightly tied to the type of water activity. Children who play and swim in irrigation canals, farmers who stand in fields irrigated with untreated water, and fishermen who wade daily are most exposed. A traveller who drinks only bottled water but swims in a natural lake in an endemic area may still become infected despite being careful about drinking.

What are the symptoms of bilharzia?

In the very early stage, within days of exposure, some people notice mild skin itching at the point of larval entry, sometimes called swimmer's itch. This passes quickly and is often dismissed. In the first weeks of a primary infection, before the worms have matured, some individuals develop a flu-like illness with fever, rash and fatigue, known as Katayama fever.

The best-known sign of S. haematobium infection is blood in the urine (haematuria). Early on the blood may be microscopic and only detectable with a urine test. Over time it becomes visible, giving the urine a tea-coloured or faintly pink tinge, most noticeably at the end of urination. Children in endemic communities often live with this and accept it as normal, which is exactly why diagnosis is delayed.

In S. mansoni infection, symptoms include abdominal pain and frequent diarrhoea, sometimes with blood. Over years without treatment, egg accumulation in the liver causes progressive fibrosis, the spleen enlarges noticeably, and fluid may build up in the abdomen. By this stage the disease has progressed to a chronic and harder-to-reverse stage.

What is the link between bilharzia and bladder cancer?

Chronic untreated S. haematobium infection creates a persistent inflammatory environment in the bladder wall that substantially raises the risk of bladder cancer. This cancer type, known as squamous cell carcinoma of the bladder, is distinct from the transitional cell carcinoma more common globally, and it has historically been closely linked to regions of high bilharzia prevalence in Egypt and North Africa.

A review published in European Urology in 2021 confirmed that bilharzia remains one of the most significant risk factors for bladder cancer in Africa. Data from Egypt show that the proportion of squamous cell bladder cancer correlates with historical bilharzia prevalence across different governorates, and this proportion has declined in parallel with control of the disease.

The important message is that early treatment with praziquantel stops ongoing tissue damage and reduces the risk of this malignant progression. A single infection treated promptly does not usually pose a long-term cancer risk. The danger comes from repeated infections or a single infection left untreated for years, allowing chronic inflammation to accumulate.

How is bilharzia diagnosed?

The classic diagnostic method is microscopic examination of a urine sample to look for parasite eggs. The urine should be collected around midday, and the last few drops of urination are the most informative because eggs concentrate there. For S. mansoni infection, stool examination is used instead of urine.

A review published in Trends in Parasitology in 2017 noted that the sensitivity of microscopy falls in light or chronic infections where egg counts are low. In these cases, serology tests measuring antibodies against the parasite remain positive for longer and help identify past exposure, while newer antigen tests including the urine CCA test offer higher sensitivity and are available in some centres in Egypt and Sudan.

Ultrasound imaging of the kidneys and bladder is useful for assessing accumulated damage in patients with suspected longstanding infection. It can reveal bladder wall thickening, calcified egg deposits and the characteristic periportal fibrosis in the liver. These imaging findings indicate chronic disease even when urine microscopy is no longer strongly positive.

How is bilharzia treated?

The treatment of bilharzia is remarkably straightforward given the damage it can cause: a single drug called praziquantel is given as a weight-based dose in a single day and is highly effective against the adult worms. Side effects are usually mild and brief, and may include abdominal discomfort, nausea and transient dizziness in the hours after taking the tablets.

Praziquantel does not kill cercariae that may have just penetrated the skin, so in the case of very recent exposure before worms have matured, the doctor may wait several weeks before prescribing the treatment, to ensure the drug has a target to act on. The timing is a clinical decision based on when exposure occurred and the severity of any symptoms.

Recovery from infection does not confer lasting immunity. Someone who returns to contact with contaminated water can be reinfected. This is why mass treatment programmes in Egypt and Sudan distribute praziquantel periodically to schoolchildren in endemic communities, rather than waiting for symptoms to appear. These programmes are a cornerstone of control and have contributed substantially to the decline in Egypt's burden.

If you are in an area where the drug is not immediately available through a public programme, praziquantel can be obtained through pharmacies in most Middle Eastern countries. The cost is modest and the treatment course is short, making it one of the most cost-effective parasitic disease treatments in existence. Do not delay seeking a prescription if you have had water exposure in an endemic area and notice any urinary symptoms. Following up with a urine test four to six weeks after treatment confirms clearance and gives both you and your doctor confidence that the infection has been fully resolved.

How do you protect yourself and your children?

The key rule is to avoid swimming, wading or playing in slow-moving or still freshwater in endemic areas. This includes irrigation canals, shallow natural lakes and some tributaries of the Nile. Fast-flowing water and treated water in chlorinated swimming pools are safe. The protective measure is about where and how you enter the water, not about the water you drink.

If you must enter water for farming or fishing, drying the skin immediately and rubbing it vigorously after leaving the water can reduce larval penetration. Rainwater and properly treated tap water are safe. Teaching children that irrigation canals and agricultural water channels are not safe for swimming is one of the most impactful and lowest-cost steps a family can take.

In communities with high endemic rates, some school health programmes offer regular testing and preventive praziquantel doses. If you live in a village near Nile canals or irrigation networks in Egypt or Sudan, ask at the local health centre whether a mass treatment programme operates in your area and whether your children have been tested recently.

What if you had past exposure and were never diagnosed?

If you grew up in an Egyptian or Sudanese village near irrigation canals and used to play in the water as a child, a screening test is worthwhile even without current symptoms. A urine dipstick or microscopy for eggs is a simple and inexpensive test. The absence of visible blood does not rule out a past or light infection.

Old infections may leave calcified eggs in the bladder wall without live worms. Antibody serology or ultrasound can reveal this evidence of past infection. Calcified eggs without live worms do not require praziquantel, which targets live adults, but they are a signal to monitor kidney and bladder function periodically with the support of a doctor.

If you have lived outside endemic areas for many years but had untreated exposure in the past, share the full geographic history with your doctor. This allows them to assess whether bladder ultrasound or kidney function testing is warranted, rather than missing a connection between an old rural childhood and a current health finding.

Sources

• Elmorshedy H, Bergquist R, Fayed A et al: Elimination of schistosomiasis requires multifactorial diagnostics: evidence from high- and low-prevalence areas in the Nile Delta, Egypt, Infectious diseases of poverty, 2020
• Barakat RM: Epidemiology of Schistosomiasis in Egypt: Travel through Time: Review, Journal of advanced research, 2013
• Elbashir HT, Mohamed Nour BY: High prevalence of urogenital schistosomiasis among schoolchildren in an irrigated area in Gezira State, Sudan: a brief report, Parasitology research, 2026
• Botelho MC, Alves H, Richter J et al: Halting Schistosoma haematobium - associated bladder cancer, International journal of cancer management, 2017
• Mantica G, Terrone C, Der Merwe AV et al: Bladder Cancer and Associated Risk Factors: The African Panorama, European urology, 2021
• Le L, Hsieh MH: Diagnosing Urogenital Schistosomiasis: Dealing with Diminishing Returns, Trends in parasitology, 2017