Schistosoma &

SchistosomiasisDr. Rafal J. Al-Saigh

Medical DoctorMB.Ch.B., MSc,

PhD Clin. Microb (Athens, Greece)

January 28th, 2008Gordana & Goldis

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

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.

Life Cycle

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: SnailFinal Host: vertebrate (Human)

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

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

12. Females release eggs.

Egg (Diagnostic Stage) characteristics

13. Eggs enter lumen of excretory organs50% passed out of body50% trapped in tissues, carried away

by blood circulation & lymph.

Eggs need 1-2 months to shed in stool or urine.

Sch. Japonicumround egg with small

lateral spine

Sch.mansoniOval egg with lateral spine

Sch. Haematobiumoval egg with terminal spine

Schistosomiasis

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).

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

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

Schistosomaiasis Granuloma

• In S. mansoni infectionsWall 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

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)

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 )

CNS complications

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

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.

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

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.