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Schistosomiasis, also known as bilharzia or ‘snail fever’, is a disease caused by parasites (worms called schistosomes) that are carried by freshwater snails. The disease affects over 240m people globally and causes an estimated 200,000 deaths a year. There are two main types of schistosomiasis: urogenital and intestinal.
The lifecycle of schistosomiasis/bilharzia
Symptoms of schistosomiasis
Complications of schistosomiasis
Who is affected by schistosomiasis?
What Unlimit Health is doing
The work we still need to do
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.
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.
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.
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.
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.
Schistosomiasis affects over 200 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.
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.
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. 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.
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.
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