Page last reviewed: 13/07/2011

Schistosomiasis is an infection that is caused by parasites called schistosomes. These parasites can contaminate sources of fresh water, such as lakes and rivers. Schistosomiasis is also known as bilharzia.

Schistosomes are small, white-grey worms between 7mm and 20mm long. They are capable of burying into human skin. They can then move into other organs of the body, such as the liver or bladder, where they lay eggs.

Acute and chronic schistosomiasis

Schistosomiasis can cause both short-term (acute schistosomiasis) and long-term (chronic schistosomiasis) symptoms.

Symptoms of acute schistosomiasis include:

  • skin rash,
  • a high temperature (fever) above 38°C (100.4°F), and
  • muscle aches.

Symptoms of chronic schistosomiasis include:

  • weight loss,
  • persistent diarrhoea, and
  • breathing difficulties.

How common is schistosomiasis?

The parasites that cause schistosomiasis are only found in tropical and subtropical regions. All cases of schistosomiasis that have been reported in Ireland developed in people who have travelled abroad.

In global terms, schistosomiasis is the second most common disease caused by parasites after malaria. An estimated 200 million people are infected worldwide, and 85% of cases occur in sub-Saharan Africa.

Cases of schistosomiasis can also be found in:

  • China,
  • Brazil,
  • Venezuela,
  • the Middle East,
  • the Caribbean, and
  • Southeast Asia.

Schistosomiasis is a disease that is associated with poverty. Poor living conditions, overcrowding and lack of sanitation, access to clean water and medical services are major risk factors for this type of infection.

Schistosomiasis can be treated with a medication called praziquantel, which kills the parasites.

There is currently no vaccine available for schistosomiasis so it is important to take precautions when travelling in parts of the world where the infection is widespread. This includes not swimming or wading in fresh water. See Prevention for more advice.


If schistosomiasis is diagnosed and treated promptly, the outlook is good. Most people will be cured after treatment with praziquantel or, at least, will experience a significant improvement in symptoms.

In parts of the world where schistosomiasis is widespread, access to medical treatment is limited and the risk of re-infection is high. Therefore, the symptoms of schistosomiasis can sometimes be fatal, particularly in people who are already vulnerable due to malnutrition or dehydration.

It is estimated that 14,000 people die worldwide each year from schistosomiasis, while a further 20 million experience serious complications.

Page last reviewed: 13/07/2011

Acute schistosomiasis

The symptoms of acute schistosomiasis usually develop several weeks after contact with contaminated water. The symptoms are not directly caused by the parasite but arise as an allergic reaction to the eggs that are laid by them.

Symptoms usually begin suddenly and include:

  • a high temperature (fever) above 38°C (100.4°F),
  • headache,
  • joint and muscle pain,
  • cough,
  • bloody diarrhoea,
  • a dark red, blotchy, raised skin rash,
  • pain in the upper right hand side of your abdomen, and
  • a general sense of feeling unwell.

Chronic schistosomiasis

The symptoms of chronic schistosomiasis can develop months or even years after contact with contaminated water.

The symptoms of chronic schistosomiasis have a number of causes, including:

  • damage to the body's organs by the parasite,
  • the immune system trying (but failing) to kill the parasites, and
  • an ongoing allergic reaction to the presence of eggs.

Symptoms of chronic schistosomiasis include:

  • bloody diarrhoea,
  • abdominal pain and/or cramps,
  • vomiting blood,
  • blood in your urine,
  • pain when urinating,
  • fatigue,
  • cough, and
  • shortness of breath when undertaking physical activities.

When to seek medical advice

Contact your GP if you develop any of the symptoms above and you have travelled in parts of the world where schistosomiasis is widespread, particularly countries in sub-Saharan Africa, such as Ghana, Malawi and Zimbabwe. 

Almost all cases of schistosomiasis that are reported in Ireland are most likely to occur in people who have recently returned from sub-Saharan Africa.

Page last reviewed: 13/07/2011

If you go to your GP with the symptoms of schistosomiasis, they will ask you about your recent travel history and whether you may have been exposed to contaminated water.

If your GP suspects that you have schistosomiasis, you will probably be referred to an expert in tropical diseases.

A diagnosis of schistosomiasis can be confirmed by taking a stool (faeces) sample and checking it for the presence of eggs.

In cases of chronic schistosomiasis, ultrasound scans are often used to check whether there is any damage to your organs.

Page last reviewed: 13/07/2011

To get a better understanding of the causes of schistosomiasis, it is useful to learn more about the life cycle of the schistosomes parasites.

Life cycle of schistosomes parasites

Schistosomes are an unusual type of parasite in that they use a two-stage system to infect humans. An infected human can pass out eggs in their urine or faeces (stools), which can survive in water for up to seven days.

Once the eggs are in the water, they hatch, releasing larva (small, maggot-like creatures). The larvae can swim and they begin to seek out freshwater snails. Upon finding a snail, the larva will enter its tissue where it matures into the next stage of development, known as cercariae.

After four to six weeks, the cercariae leave the snail. After they have left, they can survive in the water for up to 72 hours. If, during that time, the cercariae come into contact with a human, they can burrow through their skin. Once inside, they are able to move around the body through the veins and can get into the large vein that supplies blood to the liver (the portal vein).

The cercariae will mature into adult worms after four to six weeks. After mating with a male worm, the female worm will lay eggs, which may be passed out in urine and faeces, allowing the life cycle to begin again.

Adult worms can live in the human body for an average of three to five years, although there may have been cases where worms have lived in a human host for up to 30 years. The female worm will continue to lay eggs throughout her life span.

It is estimated that a single pair of schistosome worms could potentially produce 600 billion offspring during their life span.

Risk factors

Schistosomiasis is most common in rural environments that have high levels of poverty and poor sanitation, particularly where fresh water is used for irrigation.

Any source of fresh water, such as streams, rivers and lakes, can become contaminated, as can artificial structures, such as canals, reservoirs, irrigation ditches and dams.

Page last reviewed: 13/07/2011

If you are diagnosed with schistosomiasis, you will probably be admitted to hospital so that your health can be carefully monitored. This will help ensure that any serious complications you experience, such as dehydration, are picked up.

The medication that is used to treat schistosomiasis is called praziquantel. Praziquantel works by first paralysing the worms and then dissolving their outer casing, killing them. A single dose of praziquantel is usually required.

The side effects of praziquantel are usually mild and include:

  • nausea,
  • vomiting, and
  • abdominal pain.

Corticosteroids can also be used to relieve the symptoms of acute schistosomiasis as they help control the allergic reaction to the eggs that is responsible for the symptoms.

A further stool sample may be taken after four to six weeks to check whether there are still any eggs in your stools. If eggs are present, a further dose of praziquantel may be given.

Page last reviewed: 13/07/2011

Before travelling

Currently, there is no vaccine for schistosomiasis, but scientists are working on developing one that will prevent the parasite completing its life cycle in humans.

If you are planning to visit an infected area, it is a good idea to take waterproof trousers and boots with you just in case you have to cross a stream or river.

Before you leave take out adequate travel insurance for the countries that you will be visiting. When you receive your policy, check the small print to find out exactly what it is, and what is not, covered.

Make sure that your policy covers you for repatriation (entry back into Ireland) on medical grounds and check that it provides information about what to do if you become seriously ill. If possible, choose a policy with a 24-hour helpline that you can call if you become sick.

If you are travelling in Europe, make sure you have a European Health Insurance Card (EHIC), as well as travel insurance. An EHIC is free and could save you a lot of money (and hassle) if you need medical help while you are away.

While you are away

While you are away, avoid swimming in fresh water (ponds, lakes and rivers) when visiting areas where schistosomiasis is endemic (widespread). This includes popular holiday spots such as Lake Malawi. Only swim in chlorinated swimming pools or safe sea water.

Always boil or filter water using a travel kettle or a portable water filter before drinking it to kill any harmful parasites, bacteria and viruses.

If you accidentally swim or paddle in contaminated water, drying yourself vigorously with a towel may help stop the parasite from penetrating your skin. Although this may prevent infection, it should never be regarded as a preventative measure.

If you have to cross a river or go into a lake in contaminated areas, aim for clear patches of water with no vegetation and dry yourself as soon as you get out. Try to cross rivers upstream from villages and, if possible, wear waterproof shoes or boots.

Insect repellent cream provides some limited protection against infection, but it should not be used as a substitute for following the advice above.

Content provided by NHS Choices and adapted for Ireland by the Health A-Z.

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