Internal Medicine


Schistosomiasis, also known as snail fever and bilharzia, is a disease caused by parasitic flatworms called schistosomes.


Schistosomiasis, also known as snail fever and bilharzia, is a disease caused by parasitic flatworms called schistosomes.


Schistosomiasis is known as bilharzia or bilharziosis in many countries, after German physician Theodor Bilharz, who first described the cause of urinary schistosomiasis in 1851


The disease is endemic in about 75 developing countries and mainly affects people living in rural agricultural and peri-urban areas.



  • S. mansoni/S. japonicum
  • S. haematobium



The disease transmission cycle for schistosomiasis. | This image is a work of the United States Department of Health and Human Services, taken or made as part of that person’s official duties. As a work of the US Federal Government, the image is in the public domain.

Clinical features

Initial symptoms:

  • Swimmer’s itch
    • Initial itching/tingling and rash at infection site
    • Within 12 hours
  • 2-10 weeks later:
    • Fever, chills and muscle aches
    • Aching
    • Dry cough
    • Diarrhoea
    • Hepatosplenomegaly
    • Lymphadenopathy

Acute schistosomiasis (Katayama fever):

Occur weeks/months after the initial infection as systemic reaction against migrating schistosomulae as they pass through the bloodstream through the lungs to the liver.
  • Dry cough (with changes on chest X-ray)
  • Fever, malaise, muscle aches
  • Abdominal pain
  • Hepatosplenomegaly

Chronic disease:

In long established disease, adult worms lay eggs that can cause inflammatory reactions (eosinophilic reactions, proteolytic enzyme actions, etc).
  • Depending on site:

Genitourinary disease:

  • Frequent, painful or bloody urine (10 to 12 weeks after infection)
  • Inflammation and scarring of the bladder
  • Later: FibrosisUrinary tract obstruction, hydronephrosis, and kidney failure

Gastrointestinal disease:

  • Abdominal pain and bloody diarrhoea (especially in children)
  • Severe disease: Narrowing of the colon/rectum
  • Later: Fibrosis → Cirrhosis (4-8 % cases)

Central nervous system disease:

  • Brain: Seizures
  • Spinal cord: Transverse myelitis + flaccid paraplegia
Clinical pathology due to schistosomiasis (WHO)
MorbidityS. mansoni/S. japonicumS. haematobium
GeneralAcute schistosomiasisAcute schistosomiasis
Organ-specific pathologyHepatomegalyVesicular wall hardening
SplenomegalyBladder cancer
Ectopic egg granulomasEctopic egg granulomas
Alternative venous circulationKidney malfunction
Genital schistosomiasisGenital schistosomiasis
Developmental impairmentCognitive dysfunctionCognitive dysfunction
Delayed growth/stuntingDelayed growth/stunting


  • Secondary blood disorders in cases of colon damage
  • Where infection persists, bladder cancer may develop
  • Children can develop anaemia, malnutrition and learning disabilities


X-ray pelvis:

Calcification of the bladder wall on a plain x-ray image of the pelvis, in a 44-year-old sub-Saharan man. This is due to urinary schistosomiasis. | Jmarchn – CC BY-SA 3.0,

Tissue biopsy:



“There are schistosomas here. People and livestock are strictly prohibited from entering the water!”, a warning painted on a Yangtze levee in Honghu, Hubei | Vmenkov – CC BY-SA 3.0,


  • Praziquantel
  • Oxamniquine

Community management:

WHO guidelines for community treatment:
  • Everyone in the village receives treatment:
    • When >50% of village children have bloody urine
  • Only school-age children are treated:
    • When 20-50% of children have bloody urine
  • Mass treatment is not implemented:
    • When <20% of children have symptoms
Ethiopian children treated for Schistosoma mansoni | US Army Africa from Vicenza, Italy – Medical Civic Action Program in Shinile Woreda, Ethiopia, 2010Uploaded by Elitre, CC BY 2.0,

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