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Schistosomiasis (Bilharzia)

Schistosomiasis, also known as bilharzia or ‘snail fever’, is a disease caused by parasites (worms called schistosomes) that are carried by freshwater snails. In Africa, schistosomiasis/bilharzia is the most important parasitic disease of public health concern after malaria. The disease affects over 264m people globally and causes an estimated 200,000 deaths a year. There are two main types of schistosomiasis: urogenital and intestinal.

What causes schistosomiasis?

Infection occurs when 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

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 anti-worm 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.

Symptoms of schistosomiasis/bilharzia

At first, there are often no symptoms of schistosomiasis 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, coughing, malaise, headaches, rashes and body aches. Without treatment, the parasite can remain in the body for many years and can cause serious problems.

What are the symptoms and signs of schistosomiasis?

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

The schistosomiasis life cycle below shows how transmission happens


A graphical diagram showing the lifecycle of schistosomiasis, from eggs, to snails, to water, to humans.
Lifecycle of schistosomiasis, from eggs, to snails, to water, to humans. Diagram by: Unlimit Health

Long-term effects and complications of schistosomiasis

Children are in a queue holding empty urine sample containers. In the foreground, there are nine full urine sample containers. The urine is yellow in all but one, which has pink urine showing the presence of blood and the likely existence of a schistosomiasis infection.
Blood in urine is a common sign of schistosomiasis. Urine testing is an effective diagnostic tool for detecting schistosomiasis infection in both males and females. This image shows blood in one of the urine samples, a sign of schistosomiasis. Image by: Unlimit Health

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 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

A blue plastic bowl containing whole and half tablets of praziqantel and mebendazole sits on green and blue patterned fabric. Tubs of the medication are just visible.
Praziquantel and mebendazole tablets are prepared for administration by health workers, Madagascar. Image by: Unlimit Health/END Fund/Viviane Rakotoarivony

Schistosomiasis can usually be treated successfully with a short course of a medication called praziquantel, which kills the adult worms. However, treatment 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.

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.

The medication is administered by local teachers and volunteers known as community drug distributors (CDDs) through our partnerships with the ministries of health (MoHs).

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 246 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.

Poverty is both a cause and consequence of the poor health caused by schistosomiasis. 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.


What Unlimit Health is doing

A girl stands in front of a dosing pole which measures her height, determining the amount of deworming drugs she needs. District of Vatomandry, Madagascar. Image by: Unlimit Health/END Fund/Viviane Rakotoarivony

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.

In 2022 alone, working alongside ministries of health, we reached 35.1 million people with treatment. That’s 40% of the total number of people treated globally.

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. We are also a member of the Pediatric Praziquantel Consortium, a not-for-profit international public-private partnership, working to prepare for access and delivery of a potential new paediatric treatment for schistosomiasis.

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.

In 2021-22, we supported MoH in Burundi, Côte d’Ivoire, Ethiopia, Liberia, Madagascar, Malawi, Niger, Sudan, Uganda and Zanzibar to deliver 63 million treatments for schistosomiasis and soil-transmitted helminths.


How you can get involved

Estimates show that at least 251.4 million people required preventive treatment for schistosomiasis in 2021, out of which more than 75.3 million people were reported to have been treated.

With your support, even more people can be reached. Please make a donation today.

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