Schistosomiasis (Bilharzia)

What causes schistosomiasis?

People become infected the parasite’s larvae penetrate a person’s skin during contact with infested water, often through fishing, swimming, bathing and washing clothes.

The lifecycle of schistosomiasis/bilharzia

1. Infected people release parasite eggs into water (through urine or faeces).
2. Eggs hatch into larvae that infect freshwater snails.
3. Inside the snail, larvae develop into a new form that is released back into the water.
4. These larvae can penetrate human skin.
5. Once inside the body, they grow into adult worms and begin laying eggs.
6. These eggs cause inflammation, tissue damage, and long-term illness.

Without treatment, worms can live in the body for years, laying tens of thousands of eggs.

Once inside the human body, schistosome larvae develop into adult worms and the eggs they lay can become trapped in the body’s tissues. Adult worms grow to approximately 1cm in length and live in blood vessels. Without treatment with deworming medication, the worms can keep laying eggs for several years.

Eggs can pass out of the body into water, through excreta. When this happens, they release tiny larvae that need to grow inside freshwater snails for a few weeks before they’re able to infect another person. This means it’s not possible to catch the infection directly from someone else who has it, but indirectly through contact with contaminated water.

The schistosomiasis life cycle below shows how transmission happens

What are the symptoms and signs of schistosomiasis?

At first, there are often no symptoms, but within one to two months of infection, symptoms may develop including:

• Fever
• Abdominal pain (liver/spleen area)
• Bloody diarrhoea or blood in the stools or urine
• Cough
• Malaise
• Headache
• Rash
• Body aches

Long-term effects and complications of schistosomiasis

Acute schistosomiasis, also called ‘Katayama fever’, is a hypersensitivity reaction which develops several weeks after exposure in some individuals.

People who live with schistosomiasis for a long time without treatment can develop more serious health problems. This is also called chronic schistosomiasis.

Symptoms get worse in the parts of the body where the schistosoma eggs travel to, and cause infection. Chronic schistosomiasis can cause serious health problems in almost any area of the body, including the digestive, urinary, pulmonary and nervous systems.

In children, the disease can cause anaemia and stunted growth, and can affect their ability to learn and their future prospects. Many infected adults are unable to work or be fully productive due to fatigue and weakness, leading to economic hardship.

Without treatment, schistosomiasis can cause permanent organ damage, shutdown, and even death.

Examples of long-term health complications of schistosomiasis include:

• Impact on the digestive system, such as abdominal pain and swelling, diarrhoea and blood in faeces
• Impact on nutritional outcomes, such as anaemia and stunting (short height-for-age)
• Urinary and bladder problems, like cystitis, contracted bladder and bladder cancer
• Reproductive health problems, such as female genital schistosomiasis and infertility
• Problems with heart and lungs, including shortness of breath or coughing up blood
• Brain and nervous system issues, like headaches, weakness and numbness, dizziness or fits.

Schistosomiasis treatment

Schistosomiasis can usually be treated successfully with a short course of a praziquantel, a safe, effective, low-cost medicine.

The treatment kills the adult worms but does not prevent re-infection. Re-exposure to parasites is common and people will often be re-infected in areas where the disease is present. Treatment is therefore given repeatedly through mass drug administration campaigns and administered by local teachers and volunteers known as community drug distributors (CDDs) through our partnerships with the ministries of health (MoHs).

Steroid medication can also be used to help relieve the symptoms of acute schistosomiasis, or symptoms caused by damage to the brain or nervous system.

Schistosomiasis is often treated alongside other neglected tropical diseases (NTDs) such as intestinal worms, lymphatic filariasis and river blindness.

More information about how we work and our strategic plan for 2023-28 is here.

Who is affected by schistosomiasis?

Schistosomiasis affects over 253 million people worldwide. The parasite is most commonly found in sub-Saharan Africa, but also lives in parts of South America, the Caribbean, the Middle East and Asia. Local outbreaks are possible where environmental conditions allow, as demonstrated recently by renewed schistosomiasis transmission in the Mediterranean.

Schistosomiasis mainly occurs in marginalised communities that do not have access to clean drinking water or adequate sanitation. It affects those who rely on the use of infected surface water for their daily living needs such as drinking, cooking, cleaning and bathing, or their livelihoods.

Schistosomiasis prevention

There is currently no vaccine for schistosomiasis, so it’s important that people are aware of the risks and have access to services such as a safe water supply and sanitation to reduce exposure to contaminated water, and prevent contamination from taking place.

What Unlimit Health is doing

We work across multiple sectors in sub-Saharan Africa to deliver effective and robust health programmes that have a lasting impact. In our twenty-year history, through strong partnerships with MoHs, we’ve supported the delivery of one billion treatments for parasitic worm infections.

The schistosomiasis treatment programmes that we support generally target school-aged children and adults considered at risk, such as fishing communities, living in endemic regions. However, in areas with very high rates of infection, entire communities may be treated through mass drug administration

In 2024/5, we supported ministries of health in Côte d’Ivoire, Mauritania, Madagascar, Tanzania, Uganda and Zanzibar to deliver 10.5 million treatments to people affected by schistosomiasis.

As a member of the Pediatric Praziquantel Consortium, a not-for-profit international public-private partnership, we have been working on the delivery of a new schistosomiasis treatment tailored to pre-schoolers and in years to come we will be supporting countries to roll out treatment to this age group previously not reached with treatment.

Strengthening health systems

Approaches to reducing prevalence and infection severity of schistosomiasis have historically focused on disease control with preventive chemotherapy. However, as outlined in the World Health Organization NTD 2023-30 road map, there is growing recognition for the need to go beyond mass drug administration.

We therefore support a comprehensive approach to combatting schistosomiasis, moving away from intervention delivery and towards health equity and health systems strengthening. This means focusing on cross-cutting approaches, such as water, sanitation and hygiene (WASH) initiatives and a One Health approach.