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Transmission route

If infected people urinate or defecate in water, the eggs of the Schistosoma parasite enter the water and infect, develop and multiply in certain types of freshwater snails (intermediate host species). If the larval form (cercariae) of the parasites leaves the snail, they can survive in the water for 48 hours and can enter the human skin when it gets in touch with the water. After penetrating the skin, the larves develop into adult worms in the human blood vessels (capillaries of the mesenteries/bladder plexus) and start reproducing. The thousands of eggs that are released in the bladder and intestines leave the body by urination or defecation and so end up in surface water again and sustain the infection cycle. There are five main species of which the most common are Schistosoma mansoni, S. haematobium, and S. japonicum



  • At least 230 million people worldwide are infected, 120 million are symptomatic, 40 million women of childbearing age are infected (10 million women in Africa have schistosomiasis in pregnancy)

  • High prevalence in areas with poor sanitation

  • 80% of the disease burden is in Sub-Saharan Africa (freshwater, great lakes, rivers, small water bodies)

  • Endemic in 74 (resource-poor) nations, for instance in the Mahgreb region of North Africa, Sudan and Egypt (Nile River valley), some areas in the Middle East (Yemen), South America (Brazil, Suriname, Venezuela), parts of Central and West Africa, Cambodia, Laos, Indonesia and parts of China and Southeast Asia (The Philippines)

  • Increased infection level over the last years in countries such as Nigeria, Senegal, Togo, Guinea, Burkina Faso, Mauritania

  • Europe: climate warming favors transmission as well as the the presence of Bulinus (a genus of small tropical freshwater snails) in the Mediterranean area (Corsica)

  • Travelers, migrants and tourists returning from endemic areas after contact with contaminated water, military personnel returning from missions in Mali, Central African Republic, Ivory Coast

Clinical presentation


Symptoms of schistosomiasis

  1. No symptoms after infection (⅓ asymptomatic, low sensibility and specificity)

  2. After some days: a rash or itchy skin (cercarial dermatitis)

  3. Acute schistosomiasis (14-84 weeks)/Katayama syndrome (fever): rash, chills, cough, muscle aches/myalgia, fever, headache, respiratory symptoms, eosinophilia, hepato/splenomegaly

  4. Chronic schistosomiasis: fibro-obstructive disease (heptosplenomegaly, ascites, and lymphadenopathy)

  5. Exceptional cases: eggs migrate to brain/spinal cord -> seizures, paralysis, spinal cord inflammation/lesion (brain granuloma), focal epilepsy, generalized encephalopathy



Depending upon its strain, the flukes cause inflammation/scarring on internal organs.

Intestinal schistosomiasis

  • Abdominal pain, diarrhea, constipation, blood in the stool

  • Enlarged/damaged liver (fibrosis/portal hypertension/ascites)

  • Damaged intestines (bowel wall ulceration), splenomegaly

Urogenital schistosomiasis

  • Haematuria

  • Problems with urinating and increased risk of bladder cancer (bladder/ureteral fibrosis, hydronephrosis)

Female genital schistosomiasis (FGS)

  • Damaged female genital tract (lesions of cervix, Fallopian tubes, vagina) with increased risk of infections

  • Vaginal bleeding or discharge, sandy patches in mucosa, pelvic discomfort, edema, dyspareunia, menstrual disorders, and nodules in the vulva

  • Stress incontinence, pollakisuria

  • Anemia, infertility

Male genital schistosomiasis

  • Pathology of the seminal vesicles, prostate, other organs (risk of infertility)

Pediatric schistosomiasis

  • Malnutrition, poor growth, poor cognitive development, behaviour problems, iron-deficiency anaemia, poor school performance


  • Microscopical examination of stool (S. mansoni/S. japonicum eggs - Kato-Katz technique) or urine (S. haematobium eggs - Chemical reagent strips). Microscopic egg count to determine infection load.

  • Serologic test for antischistosomal antibodies (of travelers/immigrants from endemic areas without earlier treatment history), 6-8 weeks after new infection, species-specific serologic assays (ELISA/immunoblot test).

  • A new antigen test that can detect active infection in patients who have been repeatedly infected and treated based on the presence of schistosomal antigen is in development but not yet on the market.

  • Ultrasound: hepatosplenic and urinary lesions, periportal fibrosis, hypertrophy of the left liver lobe, atrophy of the right liver lobe, splenomegaly, ascites, calcifications of liver parenchyma or bladder, nodular enhancements of the cerebral mass, periportal fibrosis, et cetera.



Praziquantel (PZQ) for 1-2 days to treat infections caused by all Schistosoma species, post-treatment is sometimes suggested. Sometimes treated (in combination) with Metrifonate, Artesunate or Mefloquine.

Start treatment: at least 6-8 weeks after last exposure to potentially contaminated freshwater.

Praziquantel use during pregnancy:

  • Category B medication (no adequate and well-controlled studies in pregnant women, available evidence suggests no adverse birth outcomes).

  • WHO encourages the use of Praziquantel in any stage of pregnancy, benefit of treatment outweighs the risk.


Timely treatment of active infection gives good results (70-100%).

Worldwide 200,000 deaths annually, related to organ-damage and complication of the fibro-occlusive disease and immune stimulus of schistosome eggs.

Pregnant women

Schistosomiasis is associated with adverse fetal outcomes during pregnancy:

  • Preterm delivery

  • IUGR


  • Ectopic pregnancy, abortion

  • Anemia

  • Increased infant and maternal mortality rate

  • Pre-eclampsia

Systematic screening of female travelers of childbearing age with a relevant history of freshwater exposure is advisable.

Maternal-foetal transmission

Maternal schistosomiasis can have proinflammatory effects in maternal, placental and fetal parts. Apart from placental inflammation, endotoxemia is observed in the maternal bloodstream and even more in the placenta, which is associated with prematurity. There is evidence for the transplacental transport of schistosome antigens and related immune responses in the cord blood of newborns of infected mothers. Those children are born with increased levels of Schistosome antigen-specific IgE en B cell and an upregulation of fibrosis-associated proteins (due to cytokines production). This indicates that there is an in utero exposure to schistosome antigens. However, vertical transmission of Schistosomiasis in humans is not proved, although animal studies indicate the possibility of congenital infection with Schistosomiasis. In-depth epidemiological research on the health effects of maternal schistosomiasis on mother and fetus during pregnancy is lacking. Some (animal) studies indicate the potential morbidity of Schistosomiasis on mothers, fetuses and newborns. There is no protocol yet on effective management of the disease during pregnancy.

Fetal ultrasound markers


  • IUGR


  • Schistosomiasis is associated with a thick placenta (as is the case with CMV, Syphilis, Toxoplasmosis, B19 Parvo)


  • Hydrops fetalis (due to maternal anemia) with increased MCA Dopplers (TAMV/PSV)


  • Fetal hepatomegaly/splenomegaly (due to maternal anemia)


Differential diagnosis

  • Other helminthic parasitic diseases

  • Typhoid fever, viral hepatitis, Leishmaniasis

  • Helicobacter pylori (H. pylori) infection


Be alert to the possibility of Schistosomiasis in case of unexplained chronic urinary or digestive symptoms, or a history of contact with water in endemic countries (whatever the symptomatology).

Advice: systematic screening on Schistosomiasis

*  *  *


Colley, D.G., et al. (2014) Human schistosomiasis. The Lancet, 383(9936):2253–2264. doi:

De Laval, F., et al. (2014). Human schistosomiasis: an emerging threat for Europe. 384: 9948, p. 1094-195.

CDC on Schistosomiasis:

WHO on Schistosomiasis:

Treating Schistosomiasis during pregnancy

Ben-Chetrit, E. (2015). Schistosomiasis in Pregnant Travelers: A Case Series. Journal of Travel Medicine, 22(2): 94–98. doi: 10.1111/jtm.12165

Nour, N.M. (2010) Schistosomiasis: Health Effects on Women. Rev Obstet Gynecol. 3(1): 28–32

Salawu, O.T. & Odaibo, A.B. (2014) Maternal schistosomiasis: a growing concern in sub-Saharan Africa. Pathog Glob Health, 108(6): 263–270. doi: 10.1179/2047773214Y.0000000150

McDonald, E.A., et al (2014). Maternal Infection with Schistosoma japonicum Induces a Profibrotic Response in Neonates. Infect Immun. 82(1): 350–355. doi: 10.1128/IAI.01060-13  

Olveda, R.M., et al. (2015). A randomized double blind placebo controlled trial assessing the efficacy and safety of praziquantel for the treatment of human schistosomiasis during pregnancy. Lancet Infect Dis. 16(2): 199–208. doi: 10.1016/S1473-3099(15)00345-X


Photo credits

Image transmission cycle


Named after

​Schistosoma, a parasitic water-born flatworm

Also known as

Snail fever

Bilharziasis (by the German surgeon Bilharz in Cairo 1851)



Trematode blood flukes of the genus Schistosoma

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