Schistosomiasis is caused by several parasitic schistosome worms, leading to two major forms of clinical disease.
Urinary schistosomiasis is caused by Schistosoma haematobium, whilst intestinal schistosomiasis is caused by Schistosoma mansoni (in Africa, Middle East, the Caribbean and Latin America) or Schistosoma japonicum (in Asia). Most infected people live in poor communities without access to safe drinking water and adequate sanitation.
Schistosomiasis is endemic in 70 developing countries, and more than 200 million people are infected worldwide. S. mansoni occurs in Africa, the Middle East, the Caribbean, Brazil, Venezuela and Suriname. An estimated 90% of infected individuals live in sub-Saharan Africa, where up to 20 million people also suffer severe, chronic health consequences of the disease. A further 20,000 people die every year from schistosomiasis-related health problems, such as bladder cancer, kidney failure and liver or spleen damage.
To see country maps of schistosome infection, please visit the Global Atlas of Helminth Infections.
Eggs are excreted by human hosts in urine and faeces, and in areas with poor sanitation the parasites infect snails in the water. Snails act as intermediate hosts and excrete infective parasites that infect humans who come into contact with the infected water.
Please visit the Global Atlas of Helminth Infections for more information about the transmission dynamics of schistosomiasis.
To control schistosomiasis, the World Health Organization identifies three key groups for mass treatment: school-aged children, pre-school children and pregnant women. In communities where infection is common, all individuals at risk of infection should be offered treatment. The drug of choice to treat schistosomiasis is praziquantel, which is slightly more expensive but still relatively cheap – on average US$0.20 per treatment for a school-aged child. Praziquantel is given as a single dose, but the number of pills has to be adjusted to the size of the child. The preferred method for adjustment in schoolchildren is an inexpensive 'dose-pole'. This uses the height of the child to estimate the dosage.
School-aged children typically have the highest intensity of worm infection of any age group, with significant consequences for their health and development. The most cost-effective way to deliver deworming regularly to such children is through schools. These offer a readily available, extensive and sustained infrastructure with a skilled workforce that is in close contact with the community. To read more about school-based deworming, please visit the Global Atlas of Helminth Infections.
We are committed to making our model code available for use by other modellers. Below are links to code used in a recent publication:
Truscott, Gurarie et al. A comparison of two mathematical models of the impact of mass drug administration on the transmission and control of schistosomiasis. Epidemics 2017. The code for the Imperial College model is available here. The code for the Case Western Reserve University model is available here. This paper is focused on Schistosoma haematobium, but the model code includes a parameter set for Schistosoma mansoni.
Gurarie D, King CH (2014) Population Biology of Schistosoma Mating, Aggregation, and Transmission Breakpoints: More Reliable Model Analysis for the End-Game in Communities at Risk. PLoS ONE 9(12): e115875. The code for the model is available to download under Supporting Information.