Schistosomiasis (Bilharziasis)

  • This is the most important trematode infection in human.
  • Unlike Fasciola hepatica and other flukes that infect human by ingestion, Schistosoma infects trancutaneously.
  • All Schistosoma spp require molluscan intermediate hosts.
  • mansoni and S. haematobium are the most important species of Schistosoma in Kenya.
  • Infestation occurs in the course of washing, bathing or paddling in water containing snails that are shedding cercariae.
  • Species of Schistosoma, their distribution, reservoirs and their residence after infestation:

Name of the species

Global distribution

Other comments

S. haematobium


_Middle East



_Reservoirs: man

_Location of infestation: venus plexus of bladder.



S. mansoni


_Middle East

_S. America


_Reservoirs: man

_Location of infestation: venules of the mesentery.

S. japonica





_Reservoirs: man, dogs, cats, pigs, horses, goats

_Location of infestation: venules of the mesentery.


_South _East Asia

_Reservoirs: man

_Location of infestation: venules of the mesentery.


_Central Africa

_West Africa

_Reserviors: man, dogs.

_Location of infestation: venules of the mesentery.


  • Statistics: The size of female worms - 7 to 20 mm (males are smaller); global burden - 200 million people; life-span of the schistosome – 3 to 7yrs. The mean school prevalence of mansoni in Mbita (Kenya) - 60.5%. Prevalence of S. mansoni in Western Kenya - 16.3 to 38.8%); Prevalence of S. mansoni in Kirinyaga Kenya - 73  to 94%.
  1. Transmission
  • The Life-cycle;

_Eggs containing miracidia in feces or urine of a human host.

_Eggs hatch to release free-swimming miracidia

_Miracidia penetrate the snail

_Miracidia are transformed into sporocysts

_Sporocysts are trsnformed into free-swimming cercariae

_Cercariae swim out of the snail

_Cercariae penetrate through the human skin

_In the course of penetration through the skin cercariae lose the tail to be transformed into schistosomula.

_Schistosomula are transported to the liver in the blood and they grow into mature worms

_Male and female worms pair

_The paired worms migrate to the intestinal veins in the bowel or rectum (for all schistosoma species apart from S. haematobium which migrates to the venous plexus of the GU tract)

_They reside in these areas and lay and shed eggs.

  • Mainly asymptomatic
  • Cercarial dermatitis (at the point of entry)
  • Acute Katayama fever (mainly at the beginning of egg laying period) that ischaracterized by:





_Abdominal pain





  • Intestinal mucosal ulcerations (due to mansoni or S. japonicum) that may lead to:

_Bloody diarrhea

_papillomatous growths

_Focal fibrosis



  • Liver fibrosis
  • Cirrhosis
  • Splenomegaly
  • Hepatomegaly
  • Infertility
  • Transverse myelitis
  • Secondary bacterial infections (especially that of genital urinary tract).
  • Focal lesions
  • Portal hypertension
  • Hematemesis
  • Anemia
  • Lesions in the bladder wall (due to S. haematobium infestation) may cause:



_Urinary frequency

_UTI obstruction

_Chronic cystitis



_Squamous cell carcinoma

  • Physical examination
  • Microscopy for eggs in stool /urine (using either concentration or Kato Katz techniques)
  • Rectal snip for histological examination
  • Urine for RBC ( haematobium)
  • Hatching test ( haematobium)
  • Immunoassays
  • Barium meal (to investigate possibilities of oesophageal varices)
  • X-Ray of lower abdomen (calcified bladder??)
  • Intravenous urogram (obstructive uropathy??)
  • Abdominal ultrasound
  • For all species of Schistosma;

_Rx  Tab Praziquantel 40mg/kg BID x 1/7

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