1. TREMATODES -1-
Schistosoma
(Blood Flukes)
Doç.Dr.Hrisi BAHAR

2. Class Trematoda (Flukes)
General characteristics
►They are dorsoventrally flattened with an
oval to lancet shape.
► Others have different shapes such as the threadlike schistosomes.

3. Class Trematoda Most species are hermaphroditic.
Snails are the first intermediate hosts.
Some species require arthropods or fish as a second intermediate hosts

4. Schistosoma (Blood Flukes)
Class Trematoda
Schistosoma (Blood Flukes)
► The causative agent ofschistosomiasis or
bilharziosis.
► One of the most frequent tropical
diseases
► Occurrence depends on the presence
of suitable intermediate hosts

5. 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)

6. Schistosoma (Blood Flukes)
► Human infections result from contact with water (freshwater) and Schistosoma cercariae
► Schistosoma hematobium causes urinary
schistosomiasis.
►S. mansoni, S. japonicum,S. intercalatum, and S. mekongi are the causative agents of intestinal schistosomiasis and other forms of the disease.

7. Schistosoma (Blood Flukes) Morphology and life cycle
► The relatively thick male forms a
tegumental fold in which the threadlike
female is enclosed.
► The adult parasites live in the lumen of veins.

8. Schistosoma (Blood Flukes)

9. Schistosoma (Blood Flukes)
1-Sexually mature Schistosoma females lay
about 100–3500 eggs a day containing an
immature miracidium.
2-The miracidium within six to 10 days, remains viable for about three weeks

10. Schistosoma (Blood Flukes)
► At the site of their deposition, the eggs lie in chainlike rows within small veins.
► Some penetrate through the vascular
wall and surrounding tissue to reach the
lumen of the urinary bladder or intestine.

11. Schistosoma (Blood Flukes)
► Enzymes produced by the miracidium cause a granuloma formation .
►The eggs are shed by the definitive host in stool or urine .

12. 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

13. Schistosoma (Blood Flukes)
The cercariae upon contact with a human host,
Enzyme secretion and vigorous movements
enable them to penetrate the skin or less
frequently the mucosa when ingested with
drinking water.

14. Shistosoma miracidium

15. Schistosoma (Blood Flukes)
During the infection process, the cercaria loses its tail, sheds the surface glycocalyx, forms a new tegument, and transforms into the schistosomulum.

17. Migration of Schistosomes in 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.

18. 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.

19. Pathogenesis and clinical manifestations
The infection can be divided into the following phases:
1-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.

20. Pathogenesis and clinical manifestations
2-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 .

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

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

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

25. 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.

26. 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.

27. Clinical manifestation

28. Clinical manifestation
The main forms of schistosomiasis are
differentiated according to the localization
of the lesions:
1-Urinary schistosomiasis (urinary bilharziosis)
2-Intestinal schistosomiasis (intestinal bilharziosis)
3-Hepatosplenic schistosomiasis
4-Cerebral and pulmonary schistosomiasis
5-Cercarial dermatitis

29. Schistosoma (Blood Flukes)
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).

30. 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.

31. Schistosoma (Blood Flukes)
Therapy.
The drug of choice for treatment of schistosomiaisi is praziquantel,which is highly effective against all Schistosoma species and is well tolerated.