Schistosomiasis

Overview :

Infections associated with worms present some of the most universal health problems in the world. In fact, only malaria accounts for more diseases than schistosomiasis. The World Health Organization (WHO) estimates that 200 million people are infected and 120 million display symptoms. Another 600 million people are at risk of infection. Schistosomes are prevalent in rural and outlying city areas of 74 countries in Africa, Asia, and Latin America. In Central China and Egypt, the disease poses a major health risk.

There are five species of schistosomes that are prevalent in different areas of the world and produce somewhat different symptoms:

• Schistosoma mansoni is widespread in Africa, the Eastern-Mediterranean, the Caribbean, and South America and can only infect humans and rodents.
• S. mekongi is prevalent only in the Mekong river basin in Asia.

• S. japonicum is limited to China and the Philippines and can infect other mammals, in addition to humans, such as pigs, dogs, and water buffalos. As a result, it can be harder to control disease caused by this species.
• S. intercalatum is found in central Africa.
• S. haematobium occurs predominantly in Africa and the Eastern Mediterranean.

Intestinal schistosomiasis, caused by Schistosoma japonicum, S. mekongi, S. mansoni, and S. intercalatum, can lead to serious complications of the liver and spleen. Urinary schistosomiasis is caused by S. haematobium.

It is difficult to know how many individuals die of schistomiasis each year because death certificates and patient records seldom identify schistosomiasis as the primary cause of death. Mortality estimates vary related to the type of schistosome infection but is generally low, for example, 2.4 of 100,000 die each year from infection with S. mansoni.