Schistosomiasis dr.rafal
Transcript of Schistosomiasis dr.rafal
Schistosoma &
SchistosomiasisDr. Rafal J. Al-Saigh
Medical DoctorMB.Ch.B., MSc,
PhD Clin. Microb (Athens, Greece)
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
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, 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
• 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