By

Dr. Gamal Allam Assoc. Prof. of Immunology & Parasitology

Learning outcomes

• By the end of the lecture, you should be able to:1- Mention Causal Agent of schistosomiasis.2- Mention systematic position of Schistosoma spp.3- Mention geographic distribution of schistosomiasis.4- Enumerate Intermediate, Definitive and Reservoir hosts of

Schistosoma spp.6- Explain life cycle of Schistosoma spp.7- Mention habitat of Schistosoma spp.8- Mention mode of infection by Schistosoma spp.9- Mention pathology and clinical features of schistosomiasis.10- Diagnose schistosomiasis.11- Mention prevention and control means of schistosomiasis

Dr. Gamal Allam

Causal Agents

• Schistosomiasis is caused by digenetic blood trematodes.

• Three main species infecting humans:– Schistosoma haematobium– Schistosoma mansoni– Schistosoma japonicum

Dr. Gamal Allam

Systematic position

• Phylum: Platyhelminthes• Class: Termatoda• Genus: Schistosoma (S.)5 species of can infect human:

– S. haematobium– S. mansoni– S. japonicum– S. mekongi – S. intercalatum

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Geographic Distribution

• Schistosoma mansoni is found in parts of South America and the Caribbean, Africa, and the Middle East.

• Schistosoma haematobium in Africa and the Middle East.

• Schistosoma japonicum in the Far East.

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Geographic Distribution…… cont.

Schistosoma mansoni S. haematobium

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Morphology of Schistosoma

Stages Adult, Egg, Miracidium, Sporocyst,

Cercaria, Schistosomule

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Adult Worm

• Separate sex (male and female worms)

• The male has a gynecophoric canal in which it carries the female during the life cycle.

• 10-20 mm long.

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Egg• Oval (S. haematobium & S. mansoni) or Round (S. japonicum)

• Translucent

• Contains mature miracidium

• With terminal spine (S. haematobium), lateral spine (S. mansoni), or rudimentary lateral spine (S. japonicum)

S. haematobium S. mansoni S. japonicum

Dr. Gamal Allam

(110-170 x 40-70µm) (115-175 x 45-70µm) (70-100 x 50-70µm)

Miracidium

• Pyriform • Ciliated• ~200µm long

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Sporocyst

• Sac- like• Contain germinal cells masses

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Cercaria

• Has a body and tail • Has furcocercous (forked) tail• 400-600µm long

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Life Cycle

• In human(Definitive host), male & female mature and pair up in the liver.

• The couple migrate against the blood stream direction to favoured site where female deposit eggs: mainly mesenteric venules of large bowel & rectum (S. mansoni), mesenteric venules of small intestine (S. japonicum), or pelvic and vesical venous plexus (S. haematobium).

• About 50% of deposited eggs passed out of body and 50% trapped in tissues.

• Eggs are released with feces (S. mansoni & S. japonicum) or urine (S. haematobium) .

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Life Cycle…. cont

• In fresh water and under optimal conditions the eggs hatch and release miracidia, which swim and penetrate specific snail intermediate hosts: Biomphalaria sp. (S. mansoni), Bulinus sp. (S. haematobium), or Oncomelania sp. (S. japonicum)

• In the snail (intermediate host) asexual replication occur including 2 generations of sporocysts and the production of cercariae.

• Upon release from the snail, cercariae (the infective stage) swim, penetrate the skin of the human host , and shed their forked tail, becoming schistosomulae (Skin schistosomulae).

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Life Cycle…. cont

• The schistosomulae migrate through blood vessel to the lungs (lung schistosomulae ) and then to the liver which mature to adult worm.

• Adult worms in humans reside in the mesenteric venules in various locations, which at times seem to be specific for each species as mentioned previously .

• The females deposit eggs in the small venules of the portal and perivesical systems. The eggs are moved progressively toward the lumen of the intestine (S. mansoni and S. japonicum) and of the bladder and ureters (S. haematobium), and are eliminated with feces or urine, respectively .

Dr. Gamal Allam

Life Cycle

Intermediate and Reservoir hosts

Intermediate host

Reservoir hosts

S. mansoni Biomphalaria rodents and monkeys

S. haematobium Bulinus ------------------

S. japonicum Oncomelania dogs, cats, rodents, pigs, and goats.

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Clinical Features

• Acute schistosomiasis (Katayama's fever) occur weeks after the initial infection, especially by S. mansoni and S. japonicum. Manifestations include:– fever,– cough,– abdominal pain and diarrhea, – hepatospenomegaly,– eosinophilia.

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Clinical Features…..cont.

• Chronic infection cause granulomatous reactions and fibrosis in the affected organs, which may result in manifestations that include:– colonic polyposis with bloody diarrhea (S. mansoni).– portal hypertension with hematemesis and

splenomegaly (S. mansoni, S. japonicum);– cystitis and ureteritis with hematuria, which can

progress to bladder cancer (S. haematobium).– pulmonary hypertension (S. mansoni, S. japonicum)– glomerulonephritis (S. haematobium).– may central nervous system lesions.

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Hepatic granuloma

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Clinical Features…..cont.

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Laboratory Diagnosis

• Microscopic identification of eggs in stool or urine is the most practical method for diagnosis.

• Stool examination should be performed when infection with S. mansoni or S. japonicum is suspected.

• Urine examination should be performed if S. haematobium is suspected.

Dr. Gamal Allam

Eggs of Schistosoma spp.Schistosoma mansoni S. haematobium

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Schistosoma japonicum eggs

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Prevention and Control

• Avoidance of wading, bathing, swimming in or drinking polluted water.

• Wearing protective clothes (gloves, boots........).

• Quick and through drying of exposed skins.

• Abstinence from defecation and micturation in water canals.

• Mass treatment of all infected cases.

• Control of Snail ( intermediate host) through:

– Physical methods : changing the suitable environmental conditions like canal coverage

– Biological methods :introduction of natural enemies as competitive snails or fish

– Chemical methods using molluscicides eg: copper sulphateDr. Gamal Allam

Thank YouThank You

Dr. Gamal AllamDr. Gamal Allam