WHO updates fact sheet on Schistosomiasis (19 January 2017)

The World Health Organization (WHO) has updated its fact sheet on Schistosomiasis.

Key Messages:

Schistosomiasis is an acute and chronic parasitic disease caused by blood flukes (trematode worms) of the genus Schistosoma.

Transmission occurs when people suffering from schistosomiasis contaminate freshwater sources with their excreta containing parasite eggs, which hatch in water.

People become infected when larval forms of the parasite – released by freshwater snails – penetrate the 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’s lifecycle. Others become trapped in body tissues, causing immune reactions and progressive damage to organs.

Schistosomiasis mostly affects poor and rural communities, particularly agricultural and fishing populations. Women doing domestic chores in infested water, such as washing clothes, are also at risk. Inadequate hygiene and contact with infected water make children especially vulnerable to infection.

Schistosomiasis is prevalent in tropical and subtropical 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.

There are 2 major forms of schistosomiasis – intestinal and urogenital – caused by 5 main species of blood fluke.

Urogenital schistosomiasis is also considered to be a risk factor for HIV infection, especially in women.

Symptoms

Symptoms of schistosomiasis are caused by the body’s reaction to the worms’ eggs.

Intestinal schistosomiasis can result in

  • abdominal pain,
  • diarrhoea, and
  • blood in the stool

Liver and spleen enlargement may occur in advanced cases.

The classic sign of urogenital schistosomiasis is haematuria (blood in urine). Fibrosis of the bladder and ureter, and kidney damage are sometimes diagnosed in advanced cases. Bladder cancer is another possible complication in the later stages.

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.

WHO estimates that there are about 200 000 deaths globally each year due to schistosomiasis.

Diagnosis

Schistosomiasis is diagnosed through the detection of parasite eggs in stool or urine specimens.

Antibodies and/or antigens detected in blood or urine samples are also indications of infection.

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, known as the Kato-Katz technique.

For urogenital schistosomiasis, a filtration technique using nylon, paper or polycarbonate filters is the standard diagnostic technique.

Prevention and Control

The WHO strategy for schistosomiasis control focuses on reducing disease through periodic, targeted treatment with praziquantel through the large-scale treatment (preventive chemotherapy) of affected populations. It involves regular treatment of all at-risk groups.

Groups targeted for treatment are:

  • School-aged children in endemic areas.
  • Adults considered to be at risk in endemic areas, and people with occupations involving contact with infested water, such as fishermen, farmers, irrigation workers, and women whose domestic tasks bring them in contact with infested water.
  • Entire communities living in highly endemic areas.

Praziquantel is the recommended 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 and repeated in childhood.

Useful Links:

Link to the updated fact sheet:

http://www.who.int/mediacentre/factsheets/fs115/en/

Link to WHO programme on schistosomiasis:

http://www.who.int/schistosomiasis/en/

Link to WHO document ‘Preventive Chemotherapy in Human Helminthiasis’ (English) [PDF] (2006):

http://apps.who.int/iris/bitstream/10665/43545/1/9241547103_eng.pdf

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