Schistosoma Schistosoma

(Blood Flukes)(Blood Flukes)

TREMATODESTREMATODES-1--1-

Doç.Dr.Hrisi BAHARDoç.Dr.Hrisi BAHAR

Class TrematodaClass Trematoda(Flukes)(Flukes)

General characteristics ►They are dorsoventrally flattened with

anoval to lancet shape.

► Others have different shapes such as the threadlike schistosomes.

Class TrematodaClass Trematoda

•Most species are hermaphroditic.

•Snails are the first intermediate hosts.

•Some species require arthropods or fish as a second intermediate hosts

Class TrematodaClass TrematodaSchistosoma (Blood Flukes)

► The causative agent ofschistosomiasis or

bilharziosis.

► One of the most frequent tropical diseases

► Occurrence depends on the presence of suitable intermediate hosts

Schistosoma (Blood Flukes)

► German physician Th. Bilharz, discovered Schistosoma hematobium in human blood vessels in 1851.

► Occurs endemically in tropical and subtropical countries of Africa, South America, and Asia .

► The number of persons infected is estimated as 240 million worldwide (WHO 2011)

Schistosoma (Blood Flukes)

► Human infections result from contact with water (freshwater) and SchistosomaSchistosoma cercariaecercariae

► Schistosoma hematobiumSchistosoma hematobium causes urinary schistosomiasis.

►S. mansoni, S. japonicum,S. intercalatum, S. mansoni, S. japonicum,S. intercalatum, and S. mekongiand S. mekongi are the causative agents of intestinal schistosomiasis and other forms of the disease.

Schistosoma (Blood Flukes)

Morphology and life cycleMorphology and life cycle

► The relatively thick male forms ategumental fold in which the threadlikefemale is enclosed.

► The adult parasites live in the lumen of veins.

Schistosoma (Blood Flukes)

Schistosoma (Blood Flukes)

1-Sexually mature Schistosoma females layabout 100–3500 eggs a day containing animmature miracidium.miracidium.

2-The miracidiummiracidium within six to 10 days, remains viable for about three weeks

Schistosoma (Blood Flukes)► At the site of their deposition, the eggs lie

in chainlike rows within small veins.

► Some penetrate through the vascularwall and surrounding tissue to reach thelumen of the urinary bladder or intestine.

Schistosoma (Blood Flukes)

► Enzymes produced by the miracidium cause a granuloma formation .

►The eggs are shed by the definitive host in stool or urine .

Schistosoma (Blood Flukes)

► If the eggs are deposited into fresh water, the miracidia hatch from the eggshell and search a suitable intermediate host.

►Freshwater snails serve as intermediate hosts in which miracidia reproduce asexually, producing mother and daughter sporocysts

Schistosoma (Blood Flukes)

The cercariae upon contact with a human host,

Enzyme secretion and vigorous movementsenable them to penetrate the skin or lessfrequently the mucosa when ingested withdrinking water.

Shistosoma miracidium

Schistosoma (Blood Flukes)

•During the infection process, the the cercariacercaria loses its tail, sheds the surface glycocalyx, forms a new tegument, and transforms into thetransforms into the schistosomulum.schistosomulum.

Migration of Schistosomes Migration of Schistosomes in the Human Bodyin the Human Body

•Infection

Schistosomula penetrates subcutaneous tissues, find venous capillaries or lymph vessels, migrate through the venous circulatory system into the right ventricle of the heart and the lungs.

Migration of Schistosomes in the Human Body

It travels hematogenously into the intrahepatic portal vein branches where development into adult worms takes place as wells as male-female pairing just prior to sexual maturity.

Pathogenesis and clinical manifestations

The infection can be divided into the following phases:

1-Penetration phase1-Penetration phase :penetration of cercariae into the skin, either without reaction or—especially in cases of repeated exposure—with skin lesions (erythema, papules), which disappear within a few days.

Pathogenesis and clinical manifestations

2-Acute phase2-Acute phase, about two to ten weeks after a severe initial infection,the symptoms like,

fever, headache, limb pains,

urticaria,bronchitis, upper abdominal pain, swelling of the liver and

spleen, lymph nodes, intestinal disturbances, and eosinophilia (=Katayama syndrome) appear .

Pathogenesis and clinical manifestations

Due to release of Schistosoma antigens, the serum antibody levels (IgM, IgG, IgA)rise rapidly and immune complexes are formed immune complexes are formed that can cause renal that can cause renal glomerulopathiesglomerulopathies.

Pathogenesis and clinical manifestations

3-Chronic phase3-Chronic phase: The most significant phase in pathogenic terms begins after an incubation period of about two months with oviposition by the Schistosoma females.

The miracidia grow in the egg which remain viable for about three weeks, produce antigens which are secreted through the eggshell into the tissue.

Pathogenesis and clinical manifestations

Pathogenesis and clinical manifestations

After antigenic stimulation, T lymphocytes secrete cytokines which contribute to produce granulomatous reaction and ”pseudotubercles” above all macrophages, neutrophilic and eosinophilic granulocytes, as well as fibroblasts and aggregate around eggs.

Pathogenesis and clinical manifestations

Granulomatous proliferations protrude into

the lumen of the urinary bladder or intestine.

The granulomas are replaced by connective

tissue, producing more and more fibrous changes and scarring.

Clinical manifestationClinical manifestation

Clinical manifestationClinical manifestation•The main forms of schistosomiasis aredifferentiated according to the localization of the lesions:1-Urinary schistosomiasis (urinary bilharziosis)2-Intestinal schistosomiasis (intestinal bilharziosis)3-Hepatosplenic schistosomiasis 4-Cerebral and pulmonary schistosomiasis5-Cercarial dermatitis

Schistosoma (Blood Flukes)

Diagnosis.Diagnosis.

1-The eggs can be detected in stool specimens or in urine sediment. The eggs can also be found in intestinal or urinary bladder wall biopsies.

2-Immunodiagnostic methods are particularly useful for detecting infections before egg excretion begins.

(important for travelers returning from tropical regions).

Schistosoma (Blood Flukes)

Detection of microhematuria with test strips is an important diagnostic tool in bladder schistosomiasis.

Clinical examination with portable ultrasonic imaging equipment has proved to be a highly sensitive method of detecting lesions in the liver and urogenital tract in epidemiological studies.

Schistosoma (Blood Flukes)

Therapy.Therapy.

The drug of choice for treatment of schistosomiaisi is praziquantel,which is highly effective against all Schistosoma species and is well tolerated.