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Updated 13 February 2013

Bilharzia

Five species of the flatworm or blood flukes, also known as schistosomes, cause the main forms of human bilharzia or schistosomiasis.

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Description

  • Bilharzia is a parasitic disease caused by worms.
  • Bilharzia causes chronic ill health.
  • It is the second most prevalent tropical disease.
  • It is the eggs, and not the worm, that damage the intestines, the bladder and other organs.
  • There is a link between urinary bilharzia and a form of bladder cancer in some areas.
  • Because the disease is chronic, it adversely affects the socio-economic development of tropical and subtropical regions.
  • If bilharzia is left untreated, serious complications may occur.

Five species of the flatworm or blood flukes, also known as schistosomes, cause the main forms of human bilharzia or schistosomiasis. They are:

  • Schistosoma mansoni – intestinal bilharzia which is prevalent in 53 countries and areas of Africa, the Caribbean, the Eastern Mediterranean and South America
  • Schistosoma japonicum/Schistosoma mekongi – intestinal bilharzia
  • Schistosoma intercalatum – urinary bilharzia
  • Schistosoma haematobium – urinary bilharzia, which affects 54 countries in Africa and the Eastern Mediterranean

Only Schistosoma mansoni and Schistosoma haematobium are found in Southern Africa.

A person gets bilharzia when his/her skin comes into contact with contaminated fresh water. The parasites enter the skin, then migrate through the body to the blood vessels of the lungs and liver. From there they may advance to the veins around the bowel or bladder. The worms will lay eggs which can either be passed in the urine or faeces, or remain in the tissues in the human host. Eggs that remain in the host are usually found in the liver (S. mansoni) or the bladder (S. haematobium).

Infected people can infect fresh water if they urinate or defecate in it.

This will start a new cycle of infection when contaminated water is used in ordinary daily activities such as washing, bathing and swimming or professional activities (also see Course).

Cause

About 600 million people are at risk of becoming infected with this parasitic disease, the underlying causes of which include the following:

  • Extreme poverty
  • Unawareness of risks
  • Inadequacy or lack of public health facilities
  • Unsanitary living conditions
  • Migratory people and refugees from countries where the disease is endemic
  • Rapid urbanisation
  • Increase in tourism to places that are off the beaten track

Symptoms

Within days of becoming infected with the bilharzia parasite, a rash or itchy skin (swimmer’s itch) may appear. This normally settles spontaneously. Within another month or two a person who has been infected may experience fatigue, fever, chills, cough, muscle aches, abdominal pain, diarrhoea, dysentery and blood in the urine. This phase coincides with the maturation of the worms in the body, and is called Katayama fever.

In chronic bilhazia, it is the body’s reaction to the worm’s eggs, laid in the liver, intestine or bladder, that causes the symptoms associated with bilharzia. Eggs are rarely found in the brain.

Blood in the urine is a clear indication of urinary bilharzia, and is the commonest symptom of this type of bilharzia. In the case of intestinal bilharzia, symptoms may initially be so atypical that diagnosis is difficult. If left untreated, these symptoms can lead to serious complications of the liver and spleen.

Blood in the urine is a clear indication of urinary bilharzia. In the case of intestinal bilharzia, symptoms may initially be so atypical that diagnosis is difficult. If left untreated, these symptoms can lead to serious complications of the liver and spleen.

Prevalence

The disease commonly affects the following people:

  • Adult workers in agriculture and the freshwater fishing sector. Although these workers usually have only light infections and do not suffer from any symptoms, bilharzia infection has seriously affected the productivity of such workers in north-east Brazil, Egypt and Sudan.
  • Urinary bilharzia affects 66 million children in more than 54 countries.
  • In many areas children between 10 and 14 years of age are infected. The disease substantially affects children’s growth and school performance.

Course

Because of a lack of information or not enough attention to hygiene, people who are already infected with the parasite contaminate their fresh water supply by urinating and defecating in it. The eggs of the schistosomes in the excrement hatch when they come into contact with water and release a parasite, called the miracidium. To survive, this parasite must find a fresh water snail. Once it has found its snail host, the miracidium divides and produces thousands of new parasites or cerceriae, which the snail in turn excretes in the surrounding water. Here it can survive for 48 hours. Any person coming into contact with this water can be infected by the cercariae.

When the new parasites have entered a person’s skin (it can happen in a few seconds), they migrate to the blood vessels of the lungs. From there they migrate to the blood vessels of the liver and intestines (Schistosoma mansoni) and bladder (Schistosoma haematobium). Bilharzia continues its life cycle in the blood vessels of the intestines (in the case of intestinal bilharzia) or the bladder (in the case of urinary bilharzia) of the victim.

In 30 to 45 days a cerceriae is transformed into a long worm. The female worms lay between 200 and 2 000 eggs per day over an average of five years. It is the eggs and not the worm that cause the damage to the bladder, intestines and other vital organs, such as the liver. The body's reaction to the eggs in the liver can cause fibrosis in the liver, which in turn causes enlargement of the spleen, and dilation of some of the blood vessels, especially in the base of the oesophagus.

Risk factors

You may get infected with bilharzia if:

  • You live in or travel to areas where bilharzia occurs.
  • Your skin comes into contact with contaminated fresh water from canals, rivers, streams or lakes.

When to see a doctor

  • If you have travelled to an area where bilharzia is found.
  • If your skin has come into contact with fresh water in such an area.
  • If you have blood in your urine.

Diagnosis

  • Stool or urine samples will be examined for parasite eggs. It is better to test the urine at midday.
  • The test for blood in the urine involves using a paper strip that has been soaked in a reactive agent. It is easy to use in rural areas. In some situations, if bilharzia is common in the area and the person has appropriate symptoms, blood in the urine may be used to make a diagnosis. However, the presence of blood in the urine is not diagnostic of bilharzia, since other conditions can also cause blood in the urine.
  • A blood test is available for a more accurate diagnosis. The test is best done after 6 to 8 weeks after last being exposed to contaminated water.
  • A biopsy of the rectum may be required in intestinal bilharzia.

Treatment

Modern medicines to treat bilharzia are safe and effective. Treatment is aimed at reducing the risk of damage to body organs and usually have to be repeated. Three medicines have been used successfully:

  • Praziquantel – used to treat all forms of bilharzia. A single dose has been proven to be effective to contain the disease. Primary health care workers can safely administer it.
  • Oxamniquine – for treating intestinal bilharzia in Africa and South America
  • Metrifonate – for treating urinary bilharzia

Because of the risk of reinfection, it is important to do follow-up tests for three months until a patient is declared cured.

Prevention

  • Do not swim in fresh water when visiting areas where bilharzia is endemic.
  • Make sure that drinking water is safe by filtering or boiling it for 1 minute. Iodine treatment alone cannot guarantee safe and parasite-free drinking water.
  • Heat bath water for at least five minutes to 65 degrees C. Water that has been stored in a tank for at least 48 hours should be safe to bath in.
  • Vigorous towel drying to prevent the parasite from entering the skin is not very reliable and can be used with limited success only after very brief exposure to contaminated water.

Reviewed by Dr Andrew Whitelaw, MBBCh (Witwatersrand), MSc (UCT), FCPath (Micro) (SA) Senior registrar, Department of Microbiology, University of Cape Town and Groote Schuur Hospital

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