Epidemiology

Schistosomiasis is ranked second behind malaria, among human parasitic diseases in terms of public health and socioeconomic importance in subtropical and tropical areas (1)

WHO estimates that 200 million are infected worldwide - of these 20 million suffer severe consequences of infection and 120 million are asymptomatic (1)

• Schistosomiasis is prevalent in tropical and subtropical areas, especially in poor communities without access to safe drinking water and adequate sanitation.
  • agricultural and fishing populations are especially vulnerable
  • 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
• in regions with typical transmission patterns, 60–80% of schoolage children and 20–40% of adults can remain actively infected
• it is estimated that more than 90% of people requiring treatment for schistosomiasis live in Africa (1)

In endemic areas

• chronic schistosomiasis is the most prevalent form (due to repeated exposure to contaminated water)
• almost every long-term resident becomes infected with schistosomes at some point in their life (2)

Children are especially vulnerable since they tend to spend time swimming or bathing in water containing infectious cercariae.

• usually by the age of 2 years, initial infection with cercariae occurs. During the next 10 years, the burden of infection increases in intensity as new worms colonise the child’s body
• the highest prevalence and intensities of infection occur in young adolescents, after which both intensity and prevalence of infection generally decrease in adulthood
• high prevalence may persist among subpopulations of adults who have frequent contact with water during their daily activities—eg, laundry, bathing, fishing, washing cars (2).

Disease-related mortality is low globally, around 200,000 (0.1% of infected patients) per year.

• 90% are inhabitants of sub-Saharan Africa (3)

The 2 main forms, parasite species and geographical distribution of Schistosomiasis are as follows (1):

• intestinal schistosomiasis

• urogenital schistosomiasis

Reference:

• (1) World Health Organization (WHO). Schistosomiasis. Accessed 09/08/2017
• (2) Colley DG et al. Human schistosomiasis. Lancet. 2014;383(9936):2253-64.
• (3) Barsoum RS, Esmat G, El-Baz T. Human schistosomiasis: clinical perspective: review. J Adv Res. 2013;4(5):433-44.