Schistosomiasis


Schistosomiasis is a parasitic disease that leads to chronic ill-health. People infected with schistosomes expel the parasite’s eggs in their faeces or urine depending upon the type of the infecting parasite. In communities where no proper latrines or sanitation exist, freshwater resources in these communities may become contaminated with faeces or urine containing the eggs. Eggs hatch when they come in contact with water, thus releasing larvae called miracidia. If miracidia find the right type of snail, they use it to multiply in several cycles, eventually producing thousands of new parasites, called cercariae, which are then released from the snails to the surrounding water. When humans come into contact with water-containing cercariae, cercariae penetrate the skin and infect those humans.

Schistosomiasis is characterized as either intestinal or urogenital, depending on where the adult flukes are located. In intestinal schistosomiasis, adult worms occupy mesenteric veins, and their eggs pass into the lumen of the intestine and reach the faeces. There are four species that cause intestinal schistosomiasis: S. intercalatum, S. japonicum, S. mansoni and S. mekongi. S. haematobium causes urogenital schistosomiasis, and adult worms reside in veins draining the urinary tract, and their eggs pass out of the body in the urine.

An estimated 207 million people may have schistosomiasis in the world. The disease is endemic in tropical and subtropical areas. It is most prevalent in sub-Saharan Africa, where more than 90% of those infected live.

In the Eastern Mediterranean Region, Somalia, Sudan and South Sudan remain the most endemic countries. The disease is considered eliminated in Islamic Republic of Iran, Lebanon, Morocco and Tunisia. Low endemicity has been reached in Egypt, Iraq, Jordan, Libya, Oman, Saudi Arabia and Syrian Arab Republic. In Yemen a project is being implemented by the Ministry of Public Health to eliminate schistosomiasis from the country. The project is funded by the World Bank, and supported by WHO and Schistosomiasis Control Initiative. Three campaigns of mass drug administration using praziquantel have been implemented in the project which started in 2010 and is planned to continue until 2015.