This document discusses the parasite Schistosoma, which causes the disease schistosomiasis. It has a complex lifecycle involving human and snail hosts. The most important species that infect humans are S. japonicum, S. mansoni, and S. haematobium. Schistosomiasis causes chronic issues through egg-induced inflammation and fibrosis as the female worms produce hundreds of eggs daily that become trapped in human tissues. Symptoms and organ damage depend on the infecting species and chronic infection can lead to serious issues like liver cirrhosis and bladder cancer if left untreated.

1. Schistosomiasis
Phylum: Platyhelminthes
Class: Trematoda

2. • Parasitic trematode (flatworms) capable of causing disease in man.
Schistosomiasis (Bilharzia) is the most important of these helminth
infections, and is caused by members of the genus Schistosoma. These
parasites are important pathogens, estimated to be infecting some 200
million people in tropical and subtropical regions.
• the lifecycle of schistosomes includes two hosts: a definitive host (i.e.
human) where the parasite undergoes sexual reproduction, and a single
intermediate snail host where there are a number of asexual reproductive
stages.
• The most important species that infect man are S. japonicum, S.mansoni,
S. haematobium.
• The female worm produces 300 to 3000 eggs each day. Eggs pass into the
lumen of the intestine or bladder

3. Life cycle

4. Schistosomula larva - the migratory
larval form within the definitive host.
The schistosomulum migrates through the body, until it reaches maturity
as an adult worm. Migration through the body is through the following
route:

5. • Penetration of the skin by the cercaria and the skin migratory
phase.
An initial attachment to the skin, and finally penetration of the skin into the
epidermis using proteolytic secretions from the cercarial post-acetabular gland.
On penetration, the cercaria undergoes transformation to the schistosomulum (
cercarial tail is lost)
• The Lung Stage Schistosomulum
Is important for further migration of the parasites, parasite starts feeding on
plasma. Then migrate via blood vessels to hepatic portal vein.
• The Liver stage Schistosomulum and immature adult
Parasites have gut and become sexually mature. the adult
male and female parasites pair up, and migrate against the
flow of blood back along the hepatic portal vein to its
mesenteric branches around the intestine. (S. mansoni)

7. Egg of Schistosoma
Biomphalaria glabrata
The Miracidium
Cercaria
First twenty minutes of skin penetration

8. Distribution of S. mansoni

9. Distribution of S. haematobium

10. = Paired Adult S. mansoni worms, the darker female lying
within the gynacophoric canal of the larger male worm.
= The male S. mansoni parasites are found predominantly in
the small inferior mesenteric blood vessels surrounding the
large intestine and caecal region.
= whilst adult S. haematobium are found in the pelvic blood
vessels of the vesicle plexus, surrounding the bladder, (and
thus giving rise to urinary schistosomiasis).

11. Hepatosplenic Schistosomiasis
• Hepatosplenic schistosomiasis is a consequence of a
fibrotic reaction around egg granulomas in the liver,
and an associated enlargement of the spleen
(splenomegaly). This may occur as soon as 18 months
after a heavy infection, or as long as 20 years in light
infections. Here fibrosis in the granuloma leads to a so-
called "Pipe stem Portal Fibrosis" as the inflammatory
response spreads to portal blood vessels proximal to
pre-sinusoidal vessels containing trapped eggs. These
fibrotic reactions in turn lead to cirrhosis of the liver.
This results in portal hypertension as blood flow
through the liver is inhibited. At this point Ascites (an
accumulation of fluid in the abdominal cavity) is
common. The Portal Hypertension in turn eventually
results in enlargement of hepatic arteries, which send
out new collateral blood vessels, particularly
oesophageal varisces. At this point recovery from the
course of the disease may be irreversible due to the
liver damage. The varisces may then rupture, resulting
in massive blood loss, haemorrhagic shock and death,
or alternatively the patient may suffer repeated
episodes of variceal bleeding before succumbing.
Hepatosplenomegaly

12. Schistosome Egg Granuloma in Human Liver
The egg induced granuloma formation is a
Delayed Type Hypersensitivity (DTH or Type IV
Hypersensitivity) reaction, and, although
eventually resulting in severe pathology,
appears to be a necessary protective host
response against hepatotoxic components of
Soluble Egg Antigen
the granuloma that forms around the egg
consists mainly of a number of different type
of immune cells, including both T and B
lymphocytes, macrophages, giant cells,
epitheloid cells, mast cells, plasma cells,
fibroblasts and Eosinophils.

13. General Pathology Associated with
Schistosome Infections
• Infection with Schistosoma mansoni
• The pathology associated with infection with S. mansoni can be divided into two main areas, acute
and chronic schistosomiasis.
• Acute Schistosomiasis - Also called 'Katayama' fever. This is associated with the onset of the female
parasite laying eggs, (approximately 5 weeks after infection), and granuloma formation around eggs
trapped in the liver and intestinal wall. It resembles 'serum sickness' (i.e. acute immune complex
disease), with hepatosplenomegaly, and leucocytosis with eosinophilia. This phase of the infection
is often asymptomatic, but when symptoms do occur they include fever, nausea, headache, an
irritating cough and, in extreme cases diarrhoea accompanied with blood, mucus and necrotic
material. These symptoms , if present, last from a few weeks, to several months. It is not as
commonly associated with S. mansoni infections compared with those of S. japonicum.
• Chronic Intestinal Schistosomiasis - This and the hepatic schistosomiasis detailed below, manifest a
number of years after infection. The pathogenic reaction is a cellular, granulomatous inflammation
around eggs trapped in the tissues, with subsequent fibrosis. All areas of both the small and large
intestine may be involved, with the large intestine showing the most severe lesions, whereas severe
pathology in the small intestine is only rarely observed, even though large numbers of eggs may be
deposited here. Colonic polyps are also sometimes seen, especially in Egypt (Cheever et al 1978).
The reasons for the high prevalence of this aspect of pathology in Egypt are not clear.
• Chronic Hepatosplenic Schistosomiasis - Again, this aspect of the disease is only seen a few years
after infection. The pathology is similar to that seen in the intestine, with a cellular, granulomatous
inflammation around eggs trapped in the liver, leading to fibrosis and hepatosplenic disease. Other
organs may more rarely also contain granulomas around eggs, particularly the lungs.

14. S. haematobium Infection.
• Adult parasites are found in small venules around the
bladder and urethra, with the majority of egg deposition in
the tissues of these organs, as eggs pass through the
bladder wall, to leave the body in the urine. The disease
cause is chronic in nature, with the most frequently
affected organ being the urinary bladder, where
calcification of eggs trapped in the tissues often occurs. The
disease is characterised by blood in the urine (haematuria),
hence the infection is often refered to as 'Urinary
Schistosomiasis'. Cancer of the bladder is an important
complication of infection with S. haematobium. Eggs may
be deposited in the liver, often in high numbers, and
granuloma formation may occur, but this is much less
severe than with S. mansoni.

15. Diagnosis
• The diagnosis of schistosomiasis can be
confirmed by microscopy with egg
identification, by serology, or by consistent
radiologic findings in the appropriate clinical
scenario.

16. Treatment of Schistosomiasis
• by the use of the drug Praziquantel, a highly effective
drug which kills larval and adult worms.
• Control of schistosomiasis