Class: Trematodes (flukes)

Phylum Platyhelminthes – Class Trematoda

General characters: 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 habitat1. Blood flukes, Schistosoma species2. Liver flukes, Fasciola species3. Intestinal flukes, Fasciolopsis buski4. Lung flukes, Paragonimus species

Blood flukes Schistosoma species

Blood flukes Schistosoma species:

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

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

Eggs are responsible for the pathology associated with infections

100 250 3500 eggs/day

Diagnostic stage

MORPHOLOGY EGGSS. mansoni

S. haematobium      

S.japonicum

Schistosoma haematobium Habitat: venules of the urinary bladderDisease: Urinary schistosomiasis

Egg: Ellipsoidal withterminal spine. Diagnostic stage

Intermediate hosts: are fresh water snails Bulinus

Schistosoma mansoni

Habitat: in venules of the large intestineDisease: intestinal schistosomiasis

Egg: Ellipsoidal with lateral spineDiagnostic stage

Intermediate hosts: are fresh water snailBiomphalaria

Schistosoma japonicum

Habitat: venules of the small intestineDisease: oriental schistosomiasis

Egg:round with rudimentary spine laterallyDiagnostic 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.

Hepatosplenic Schistosomiasis : S. mansoni and S. japonicum

Several years after initial infection Granulomas form within the liver and biliary tree Hepatosplenomegaly portal hypertension – liver failure

Intestinal Schistosomiasis 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 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

Chronic Disease

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