This document summarizes information about Schistosoma worms and Schistosomiasis (Bilharzia). It describes the classification, morphology, and life cycle of Schistosoma, which involves a snail intermediate host and human final host. Symptoms in humans include acute infection reactions or chronic complications in organs like the liver, intestines, bladder due to egg-induced immune responses. Diagnosis involves microscopic detection of eggs in stool/urine or other tests. Praziquantel is the primary treatment, while prevention focuses on avoiding contaminated freshwater sources.

1. Schistosoma
&
Schistosomiasis
Dr. Rafal J. Al-Saigh
Medical Doctor
MB.Ch.B., MSc,
PhD Clin. Microb (Athens, Greece)

2. January 28th
, 2008
Gordana & Goldis

3. Classification
• Phylum: Platyhelminthes (flatworms)
• Subclass: Digenea (alt. gen. seen in life
cycle)
• Order: Strigeida
• Family: Schistosomatidae (blood flukes)
• Subfamily: Schistosomatinae
• Genus: Schistosoma
• Species: S. mansoni
S. japonicum
S. haematobium

4. Morphology
• Enlongated and resemble roundworms, living in blood vessels,
have oral and ventral suckers, .
• Male: 6 to 22 mm, long and has a cylindrical appearance but
flattened behind the ventral sucker ,because it is incurved
ventrally to form a gynaecophoric canal, also has several testes
behind the ventral sucker.
• Female: 12 to 26 mm, longer and
more slender than male and
projecting free at each end, but
enclosed in the middle, also has
ovary & uterus with small number
of eggs.

6. Life Cycle

7. Life Cycle
1. Parasite eggs released into freshwater
(from human urine, feces)
2. Eggs hatch  ciliated miracidia, free
swimming
3. Miracidia find & infect snail host
(Intermediate Host)
4. Each miracidia transforms into many fork-
tailed, free swimming forms called
cercariae within 4-6 weeks of entering
snail.
Miracidia larva
with cilia
There are Two hosts:
Intermediate Host: Snail
Final Host: vertebrate (Human)

8. 5. Cercariae (Infective Stage) leave
snail and move into water for up to 18
days.
6. Cercariae find a human host,
penetrate skin, and differentiate into
larval forms called schistosomulae.
7. Migrate through the host’s skin, gain
access to the lymphatic system.
8. Travel to the lungs (stay 3-8 days
and ~70% are eliminated)
9. Migrate to liver portal system, mature
into male & female adults
Cercariae with forked tail

9. 10. In liver, male & female pair up  female inserts
herself into the gynecophoral canal of male
 they are now ‘paired’.
11. Migrate to favoured sites:
S. mansoni – mesenteric venules of
large bowel & rectum
S. japonicum – mesenteric veins of the
small intestine
S. haematobium – perivesical venous plexus
surrounding the bladder
Lifespan of the adult worm ranges from 5 -10 years
Paired male &
female

10. 12. Females release eggs.
Egg (Diagnostic Stage) characteristics
13. Eggs enter lumen of excretory organs
50%  passed out of body
50%  trapped in tissues, carried away
by blood circulation & lymph.
Eggs need 1-2 months to shed in stool or urine.
Sch. Japonicum
round egg
with small
lateral spine
Sch.mansoni
Oval egg with
lateral spine
Sch. Haematobium
oval egg with terminal spine

11. Schistosomiasis

12. Schistosomiasis, Bilharzia
• Parasitic disease caused by Schitosoma species
• Affects many people in developing countries
• Can contract it by wading or swimming in lakes &
ponds infested with the parasite’s snail host.
• First described by German pathologist
• Theodore Maximilian Bilharz
• In Egyptian patients who had died from the
disease (in their liver portal system &
bladder).

13. Acute Infection
(Early)
• Cercariae penetrate skin  rash
- called schistosome or swimmer’s itch.
• Eggs laid in target organs release antigens
 cause fever
- fever
- urticaria
- malaise
- diarrhea

14. Chronic Infection
(Late)
Symptoms of chronic infection caused by
eggs that travel to various parts of body
Eggs remain trapped in host tissues 
secrete Ags  granulomatous inflammatory
immune response
Fibroblasts mediate collagen deposition in
the granuloma, leading to fibrosis

15. Schistosomaiasis
Granuloma

16. • In S. mansoni infections
Wall of colon is damaged as eggs pass through it
• Inflamm. response  ulcers, inflammatory
polyps
• Clinically: diarrhea, abdominal pain
• Eggs can also accumulate in the appendix
• Can lead to appendicitis

17. Hepatosplenic schistosomiasis
•Eggs carried by portal circulation  liver
•Granulomatous response
•Granulomas are walled off with fibrous
tissue  fibrosis obstructs portal veins 
portal hypertension
• Esophageal varices bursting can cause
bleeding untill death.
• Splenomegaly (due to fibrosis)

18. Genitourinary complications
• Eggs lodge themselves in wall of bladder & can
develop into polyps
• Polyps can erode, ulcerate & cause hematuria
(blood cells in urine)
• Eggs lodge in ureters and urethra, cause lumps
and lesions  kidney failure
• Eggs lodge into ovaries, the uterus, cervix,
fallopian tubes  lumps  complications incl.
infertility
(For the men: eggs can also lodge into the testes
and the prostate )

19. CNS complications
S. haematobium and S. mansoni can
migrate to the spine
S. japonicum found in the brain and
causes encephalopathy

20. Diagnosis
1. Microscopic Detection of eggs in stool or
urine sample.
2. Serological tests
3. Antigen tests: Detect antigens in blood
with immunoelectrophoresis.
4. PCR
5. Intradermal skin test (schistosomian
skin test): become positive after few
months of infection.

21. Treatment
Praziquantel
• Extremely well tolerated, few side effects
• Broad-spectrum antihelminthic drug
• Resistance has been reported also
Metrifonate  against S. haematobium
Niridazole  against S. japonicum
Oxamniquine  against S. mansoni
• Recommend combination of 2 drugs

22. Prevention
For travelers it’s easy- don’t swim in fresh, stagnant
water (running water is better, still not safe).
Harder in endemic areas  people are dependent on
nearby freshwater.
Focused on education, eliminating snail nesting
grounds
Molluscicides can be used to eliminate snails.