Class: Trematodes (flukes)
Phylum Platyhelminthes – Class Trematoda
General characters:
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Dorsoventrally flattened typically leaf shaped
have an oral and a ventral sucker used for attachment and
movement.
Bifurcate intestine
complex life cycle with multiple hosts.
mollusc is usually 1st intermediate host
definitive host is a vertebrate
most are hermaphroditic except blood flukes.
TREMATODA
According to their habitat
1. Blood flukes, Schistosoma species
2. Liver flukes, Fasciola species
3. Intestinal flukes, Fasciolopsis buski
4. Lung flukes, Paragonimus species
Blood flukes
Schistosoma species
Blood flukes Schistosoma species:
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They differ from other trematodes in that they have separate sexes.
Only trematodes that live in the blood stream of warm-blooded hosts
Definitive host: Human
Intermediate host: Snail
Reservoirs: monkeys, rodents, cats, dogs, cattle, horses, swine, wild
mammals
The human disease known as shistosomiasis , Bilharzia, Bilhariaziasis
In 1852 the German parasitologist, Theodor Bilharz, made the first
discovery of schistosomes (S. haematobium) while working in Egypt
Eggs are responsible for the pathology associated with infections
Human Blood flukes: Three major species
Schistosoma haematobium
 Schistosoma japonicum
 Schistosoma mansoni
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Blood flukes
Transmission
Morphology:
1- All species roughly similar.
2- Sexes are separate (dioecious).
3- size 0.5-2.5 cm in length.
3- Males short and wide, females long, thin.
4- Female adults reside in gynecophoral canal formed by male
body.
Morphology
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Eggs are responsible for the pathology associated with
infections
100
250
3500 eggs/day
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Diagnostic stage
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MORPHOLOGY EGGS
S. haematobium
S. mansoni
S.japonicum
Schistosoma haematobium
Habitat: venules of the urinary bladder
Disease: Urinary schistosomiasis
Egg: Ellipsoidal with
terminal spine.
Diagnostic stage
Intermediate hosts: are fresh water snails Bulinus
Schistosoma mansoni
Habitat: in venules of the large intestine
Disease: intestinal schistosomiasis
Egg: Ellipsoidal with lateral spine
Diagnostic stage
Intermediate hosts: are fresh water snail
Biomphalaria
Schistosoma japonicum
Habitat: venules of the small intestine
Disease: oriental schistosomiasis
Egg:round with rudimentary spine laterally
Diagnostic stage
Intermediate host: are fresh water snail Oncomelania
Life stages
Cercaria in the water
Infective stage
Symptoms:
 The first symptom is a localized dermatitis, often observed
following cercarial penetration of the skin
 It is characterized by itching and local edema, which usually
disappear after 4 days Following skin penetration.
The symptoms of human schistosomiasis appear in 3 phases:
 Migration phase,
 Acute phase
 Chronic phase
1- The migration phase (from penetration to egg production)
 There are often no symptoms
 It can be characterized by toxic reactions and pulmonary
congestion accompanied by fever.
 This phase may last 4-10 weeks, during which the worms
migrate from the lungs to the liver where they reach sexual
maturity and mate.
2. The acute phase (begins at egg production)
Symptoms such as blood stools (S. mansoni and S. japonicum)
and hematuria (S. hematobium) are caused by passage of eggs
through the intestinal and urinary bladder walls.
Chronic Disease
Hepatosplenic Schistosomiasis :
S. mansoni and S. japonicum
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Several years after initial infection
Granulomas form within the liver and biliary tree
Hepatosplenomegaly
portal hypertension – liver failure
Intestinal Schistosomiasis
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Adults migrate to intestinal wall
Lay eggs which migrate into intestinal lumen and out into stool
Severe anemia from chronic GI blood loss
Chronic Disease
S. haematobium
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Several years after infection
Adults migrate to small venules around the bladder and ureter
Eggs are deposited into surrounding tissue and penetrate out into
bladder
Causes calcifications where eggs are trapped
Characterized by hematuria
Leads to cancer of bladder
Granuloma or pseudotubercle:
forms around each egg or cluster of eggs; the result of leukocyte
infiltration and secretion of fibroblast growth factors Small
abscesses, accompanied by occlusion of small blood vessels,
lead to necrosis and ulceration.
Intestinal schistosomiasis: eggs in the wall
of the gut
Schistosoma egg in the liver : granuloma
formation
CLINICAL DIAGNOSIS
Haematuria
Laboratory Diagnosis:
1- Microscopic identification of eggs in stool or urine is the most
practical for the diagnosis:
S. haematobium eggs in urine are ellipsoidal with a terminal spine.
S. mansoni eggs in feces are also ellipsoidal but with a lateral spine.
S. japonicum eggs are more round with rudimentary spine laterally.
2- Tissue biopsy (rectal biopsy for all species and biopsy of the
bladder for S. haematobium) may demonstrate eggs when stool
or urine examinations are negative.
3- Serological tests are of value in the diagnosis of
schistosomiasis when eggs cannot be found.
Swimmers Itch:
• An interesting aspect of schistosome biology concerns cercarial
dermatitis or swimmer’s itch
• The condition is caused when cercariae of blood flukes that
normally parasitize aquatic birds and mammals penetrate the
human skin, sensitizing the areas of attack and causing pustules
and an itchy rash
• Since humans are not suitable definitive hosts for these flukes,
the cercariae do not normally enter the blood stream and mature
• Instead, after penetrating the skin, they are destroyed by the
victim’s immune response
• Allergenic material released from dead and dying cercariae
produce a localized inflammatory reaction
Cercarial Dermatitis
(Swimmer’s Itch)
Due to cercaria of avian schistosomes
Avian (bird) schistosomiasis