Download S. japonicum

Schistosome
Introduction

Schistosome (blood fluke) causes
schistosomiasis




first discovered by the German parasitologist
Theodor Bilharz in 1852 in Egypt
Dated back to ancient Egypt and about 2000
years ago in China
over 200 million people in the world infected
600 million people are at risk
Introduction

Six species affecting human being

Schistosoma japonicum

S.mansoni

S.haematobium

S.intercalatum

S.mekongi

S.malayensis : parasite of humans (rarely) and other animals. A
recently described 'new' species
Introduction


Three species of significant medical importance :
 S. mansoni: Africa, Arabia, S. America, Caribbean
 S. haematobium: Africa, Middle East
 S. japonicum: China, the Philippines, southern Japan, Central
Sulawesi (Indonesia)
Different homing orientation :
 S. mansoni: Mesenteric veins
 S. haematobium: Vesical plexus
 S. japonicum: Superior mesenteric veins
Global
Epidemiology
Purple: S.mansoni
Africa
South
America
Blue: S.intercalatum
Asia
Africa
Orange: S. haematobium
Green: S. japonicum
Red: S. mekongi
S. japonicum still endemic in China
7 endemic provinces with 119 endemic counties
Morphology

“schisto-” means “split”




Dioecious worms
Gynecophoral canal in male –
 Pheromone from the male is necessary for the development of
female worms
Incomplete digestive system: mouth, esophagus , gut
Some variations
between species
Morphology
The male adult worm of S.
japonicum is slightly larger than the
other 2 species at ~ 1.2cm by 0.5mm
Two suckers
maintains its position in the
blood vessels－－
the ventral, and larger oral
suckers
Female adult worm



Morphology
S.japonicum female parasite is about 2cm by
0.4mm
Eggs in the uterus
 S. mansoni: a single egg is shown,
usually 1 - 3

S. haematobium: many more are seen
(between 20 - 30)
 S. japonicum: 50 or more eggs
Dark grey color because of the metabolic RBC
in the digestive duct
Eggs of S.japonicum






Morphology
Average size 89×67µm
Oval or sub-spherical
Pale yellow or yellow brown
Small lateral spine
No operculum
Embryonated, contains
mature miracidium when
discharged
Eggs
Morphology
Miracidium
Morphology
A ciliated, swimming larva
Size about 99×35µm
The germinal cells will become
sporocysts
Tropism – toward limpidity ;
phototrophic
Cercaria



Free- swimming
a forked tail
penetrating glands
Morphology
C. sinensis
F. buski
S. japonicum P. westermani
Cercariae of trematodes
Life Cycle
Life Cycle


Mode of infection: penetration of the skin
Migration: stay in skin(5-10h) convert to schistosomula 
subcutaneous venules pulmonary circulation  heart  systemic
circulation  portal vein  mesenteric vein

Diagnostic stage: egg

One intermediate host -- Oncomelania hupensis (S. japonicum)
Biomphalaria (S. mansoni )
Bulinus (S. haematobium )

Infective stage: Cercaria

Lack of metacercaria stage


no redia
two generations of sporocyst
Life Cycle


Reside in portal system, superior mesenteric vein or
vesical plexus
Tissue-residing ova (the main result for pathology) –
15-63% in tissue (liver and intestine)

Instant hatching of the discharged egg in water

A variety of reservoir hosts -- zoonosis
Life Cycle
Residing place (mesenteric vein )
Intermediate host
Oncomelania hupensis
Eggs in the vein
Pathogenesis



Schistosomiasis is an immune disease
All stages in host may be pathogenic: cercaria,
schistosomulae, egg and adult
The main pathogenic factor is the egg




Deposit in important organs – liver, intestine,etc
Formation of egg granuloma
Accumulation of eggs (thousands of eggs per day)
Ectopic migration – brain, lung




Pathogenesis
Skin - “swimmer’s itch” just for a short period after cercaria
penetration –type I & IV allergic reaction
Transient fever and coughing -- mechanically damage and allergic
reaction to the metabolic materials of schistosomulae
Phlebitis caused by adult worm (rarely) and glomerulonephritis
caused by the type III hypersensitivity to the metabolic materials
to adult worms
The eggs induced granuloma formation is a Delayed Type
Hypersensitivity (Type IV Hypersensitivity) reaction
 Although eventually resulting in severe pathology, appears to
be a necessary protective host response against hepatotoxic
components of Soluble Egg Antigen (SEA).
Papules caused by the penetration of cercariae
Pathogenesis
Egg granuloma in liver
Fibrosis of portal vein
Eggs of S. japonicum in brain
Clinical features

Acute schistosmiasis
 May occur 5-8 weeks after the initial infection


Allergic reaction to first release of the eggs called
Katayamu fever
Enlarged spleen and tender liver
Clinical features

Chronic schistosomiasis – immune modulation period
 Thickening of colon with tiny ulceration

Liver and spleen enlargement

Occasionally diarrhea, anemia,wizened
Clinical features

Advanced schistosomiasis – hepatosplenic schistosomiasis -- usually
happens 5 years after infection

Irreversible liver and spleen enlargement with abnormal function
of these organs



Increased pressure in veins that drain upper intestine with risk of
bursting of these veins. upper gastrointestinal bleeding may cause
death
Cerebral granulomatous disease may be caused by ectopic S.
japonicum eggs in the brain
In child, it may cause nanoid
Advanced schistosomiasis
patients


ascites
Splenomegaly
Immunity

Non-sterilized immunity


Concomitant immunity: Concomitant immunity has long
been considered a feature of schistosome infections and
describes the phenomenon where by the adult worms can
survive happily in the mesenteric veins where as the host
seems to be resistant to secondary infection.
Age-related immunity in human
Diagnosis


Etiological diagnosis
 Sedimentation hatching method
– first choice
 Kato’s smear method for EPG
 Rectal biopsy – must distinguish live or dead egg
Immunological diagnosis
 COPT – CircumOval Precipitation Test
 Intracutaneous test
 ELISA, IHA, etc
Man's arm showing
positive skin test for
schistosome
Intracutaneous test
Control methods

Treat both human and the reservoir animals, such as
buffalo, swine etc ---praziquantel

Feces (egg) control—avoid being discharged into water

Snail control---molluscicides

Ask people to avoid contacting with water that contained
the snails and cercariae