Schistosomiasis

  • a parasitic disease that causes a wide range of non-specific symptoms 
  • symptoms include fever and diarrhea in the acute phase, and damage to internal organs in the chronic phase
  • affects 78 countries, with 240 million people infected
  • second to malaria in terms of economic burden in countries where the disease is endemic

Schistosomiasis is an acute and chronic disease, also known as Bilharzia or snail fever. It is caused by different species of blood flukes of the genus Schistosoma, with an estimated 700 million people at risk of infection. The disease burden is difficult to estimate because of hidden pathologies such as bladder and kidney failure or bladder cancer. Estimates therefore vary widely, between 20,000 and 200,000 deaths per year,1 with up to 70 million disability-adjusted life years2 (DALY3: an estimate of the number of healthy life years lost). 

The disease is transmitted by freshwater snails  that release larval forms of the parasite. As a consequence, schistosomiasis is most prevalent in poor communities in tropical and sub-tropical areas, where access to safe drinking water and adequate sanitation are scarce. As children tend to spend time swimming or bathing in water, the worms infect a large proportion of children under the age of 14 in many areas.

The presence of the intermediate host (the freshwater snail) makes the disease difficult to eliminate. To reduce and prevent morbidity, preventive treatment is therefore required, and should be repeated over a number of years. 

The only drug currently available is praziquantel, which is safe and effective. However, it has already been demonstrated in the laboratory that worms can develop drug resistance,5 which would leave the infection untreatable. In addition, praziquantel treatment is suitable only for adults and school-aged children, as younger children cannot swallow the existing tablets because of their size and bitter taste. The PDE4NPD consortium therefore aims to find and develop novel drugs against schistosomiasis.  
 


References and further reading

  1. World Health Organization; Schistosomiasis fact sheet
  2. King and Dangerfield-Cha; The unacknowledged impact of chronic schistosomiasis; Chronic Illn. 2008
  3. World Health Organization; Health statistics and information systems
  4. Centers for Disease Control and Prevention; Schistosomiasis life cycle
  5. Fallon and Doenhoff; Drug-resistant schistosomiasis: resistance to praziquantel and oxamniquine induced in schistosoma mansoni in mice is drug specific; Am. J. Trop. Med. Hyg 2004