Schistosomiasis, or bilharzia, is a parasitic disease caused by trematode flatworms of the genus Schistosoma. Larval forms of the parasites, which are released by freshwater snails, penetrate the skin of people in the water. It can cause serious, long-term illness. It can cause serious long-term illness.
There are two major forms of schistosomiasis – intestinal and urogenital – caused by five main species of blood fluke.
An estimated 700 million people worldwide may be at risk of infection as their agricultural, domestic and recreational activities expose them to infested water.
Symptoms of schistosomiasis are caused by the body's reaction to the worms’ eggs, not by the worms themselves.
Intestinal schistosomiasis can result in
- abdominal pain
- blood in the stool
Liver enlargement is common in advanced cases, and is frequently associated with an accumulation of fluid in the peritoneal cavity and hypertension of the abdominal blood vessels. In such cases there may also be enlargement of the spleen.
The classic sign of urogenital schistosomiasis is haematuria (blood in urine). Fibrosis of the bladder and ureter, and kidney damage are common findings in advanced cases. Bladder cancer is also a possible late-stage complication. In women, urogenital schistosomiasis may present with genital lesions, vaginal bleeding, pain during sexual intercourse and nodules in the vulva.
In men, urogenital schistosomiasis can induce pathology of the seminal vesicles, prostate and other organs. This disease may also have other long-term irreversible consequences, including infertility.
In children, schistosomiasis can cause anaemia, stunting and a reduced ability to learn, although the effects are usually reversible with treatment.
Schistosomiasis is a chronic, parasitic disease caused by blood flukes (trematode worms) of the genus Schistosoma.
People become infected when larval forms of the parasite – released by freshwater snails – penetrate their skin during contact with infested water.
In the body, the larvae develop into adult schistosomes. Adult worms live in the blood vessels where the females release eggs. Some of the eggs are passed out of the body in the faeces or urine to continue the parasite life-cycle. Others become trapped in body tissues, causing an immune reaction and progressive damage to organs.
Control of schistosomiasis is based on drug treatment, snail control, improved sanitation and health education.
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.
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.
Schistosomiasis is diagnosed through the detection of parasite eggs in stool or urine specimens.
For urogenital schistosomiasis, a filtration technique using nylon, paper or polycarbonate filters is the standard. Children with S. haematobium almost always have microscopic blood in their urine and this can be detected by chemical reagent strips. Asking children about a history of blood in their urine can also be used to identify communities at high risk of infection, therefore assisting in mapping priority areas for intervention.
The eggs of intestinal schistosomiasis can be detected in faecal specimens through a technique using methylene blue-stained cellophane soaked in glycerine or glass slides.
For people from non-endemic or low transmission areas, serological and immunological techniques may be useful in the detection of infection.
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.
Praziquantel is the only available treatment against all forms of schistosomiasis. It is effective, safe and low-cost. Even though re-infection may occur after treatment, the risk of developing severe disease is diminished and even reversed when treatment is initiated in childhood.
Praziquantel has been used successfully over the past 20 years to control schistosomiasis in Brazil, Cambodia, China, Egypt, Morocco and Saudi Arabia.
With the rise in eco-tourism and travel “off the beaten track”, increasing numbers of tourists are contracting schistosomiasis. At times, tourists present with severe acute infection and unusual problems including paralysis.
Urogenital schistosomiasis is also considered to be a risk factor for HIV infection, especially in women.