Schistosomiasis Factsheet
January 2012
Key facts
- Schistosomiasis is a chronic disease caused by parasitic worms.
- In the WHO Western Pacific Region, four countries have ongoing transmission of schistosomiasis: Cambodia, China, the Lao People's Democratic Republic, and the Philippines.
- Of the over 230 million people who require treatment for schistosomiasis every year according to global guidelines, approximately 617,000 live in the WHO Western Pacific Region.
- People are at risk of infection due to agricultural, domestic and recreational activities which expose them to infested water.
- Hygiene and play habits make children especially vulnerable to infection.
- Clean drinking water and adequate sanitation would reduce infective water contact and the contamination of water sources.
- Schistosomiasis control focuses on reducing disease through periodic, targeted treatment with praziquantel.
Transmission
- 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.
Epidemiology
- Schistosomiasis is prevalent in tropical and sub-tropical areas, especially in poor communities without access to safe drinking water and adequate sanitation
- It is estimated that at least 90% of those requiring treatment for schistosomiasis live in Africa, while less than 1% live in the WHO Western Pacific Region.
- There are two major forms of schistosomiasis – intestinal and urogenital – caused by five main species of blood fluke (see table).
- Schistosomiasis particularly affects agricultural and fishing populations.
- Women doing domestic chores in infested water, such as washing clothes, are also at risk.
- Hygiene and play habits make children especially vulnerable to infection.
- 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.
Symptoms
- 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, diarrhoea, and 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.
Diagnosis
- Intestinal schistosomiasis is diagnosed through the detection of parasite eggs in stool specimens.
- 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.
Prevention and control
- Prevention and control of schistosomiasis is based on preventive treatment, snail control, improved sanitation and health education.
- The WHO strategy for schistosomiasis control focuses on reducing disease through periodic, targeted treatment with praziquantel.
- This involves regular treatment of all people in at-risk groups. Treatment should be complemented with health education, as well as access to safe water and good sanitation.
- Groups targeted for treatment are:
- school-aged children in endemic areas;
- people with occupations involving contact with infested water – such as fishermen, farmers, irrigation workers;
- women whose domestic tasks bring them into contact with infested water;
- entire communities living in highly endemic areas.
- The frequency of treatment is determined by the prevalence of infection in school-age children.
- In high-transmission areas, treatment may have to be repeated every year for several years.
- The aim is to reduce disease. Periodic treatment of at-risk populations will cure mild symptoms and prevent infected people from developing severe, late-stage chronic disease.
- 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.
- Subsequently, some countries have succeeded in interrupting schistosomiasis transmission.
WHO's response
- WHO’s work on schistosomiasis is part of an integrated approach to the control of neglected tropical diseases.
- Although medically diverse, neglected tropical diseases share features that allow them to persist in conditions of poverty, where they cluster and frequently overlap.
- WHO coordinates the strategy of preventive chemotherapy in consultation with collaborating centres and partners from academic and research institutions, the private sector, nongovernmental organizations, international agencies and other United Nations organizations.
- WHO also develops technical guidelines and tools for use by national control programmes.
- Working with partners and the private sector, WHO has advocated increased access to praziquantel and resources for implementation.
- These efforts enabled at least 28 countries to implement preventive chemotherapy for schistosomiasis in 2010, including all four countries endemic in the WHO Western Pacific Region.
- The four countries in the Western Pacific Region target all people living in endemic communities instead of only school-aged children. Thus, in 2010, they treated over 3.37 million people. This represented full coverage of endemic areas in Cambodia, China, and the Lao People's Democratic Republic. The Philippines, which only covered 38% of targeted people, plans to scale up treatment in the future.