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One of The Most Important Human Parasitic Infection In Terms of Morbidity & Mortality ACCOUNTED FOR MOST OF THE DISEASES BY THE WORLD HEALTH ORGANIZATION - PowerPoint PPT Presentation

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SCHISTOSOMES. One of The Most Important Human Parasitic Infection In Terms of Morbidity & Mortality ACCOUNTED FOR MOST OF THE DISEASES BY THE WORLD HEALTH ORGANIZATION ONLY SECOND MALARIA. Globetrotting Parasites that Continue to Spread and Cause Disease.

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One of The Most Important Human Parasitic Infection In Terms of Morbidity & Mortality ACCOUNTED FOR MOST OF THE DISEASES BY THE WORLD HEALTH ORGANIZATION

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One of The Most Important Human Parasitic Infection In Terms of Morbidity & Mortality



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Globetrotting Parasites that Continue to Spread and Cause Disease

  • First discovered ( the egg form) in 1851 by a German pathologist while working in Egypt.

  • The origin of this parasite remained unclear but it’s believed that it might have been originated from parasites of hippos in Africa and Asia.

  • Causing Schistosomiasis, also known as bilharziasis or snail fever, is a primarily tropical parasitic disease.

  • According to the WHO, 200 million people are infected and 120 million display symptoms. Another 600 million people are at risk of infection. Schistosomes are prevalent in rural and outlying city areas of 74 countries.

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  • Kingdom: Animalia- Phylum: Platyhelminthes- Class: Trematoda- Subclass: Digenea- Order: Strigeiformes- Family: Schistosomatidae- Genus: Schistosoma

  • Species: S.haematobium, S.mansoni, S.japonicum

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Geographic Range

  • Currently, 21 species of this genus have been recognized.

  • Schistosoma do not thrive in fast running rivers and turbulent waters—their habitat is slow moving or still water where aquatic plants proliferate and provide snails with food.

  • According to Dr.Bates, we could careless about most of them except for these 3 significant ones from clinical point of view : Schistosomamansoni, S. japonicum and S. hematobium.

  • The three species of Schistosoma have different geographic distributions :

    - Schistosomamansoni occurs in Africa, the Middle East, the Caribbean, and in Central and South America.

    - Schistosomajaponicum is restricted to the Far East.

    - Schistosomahaematobium occurs in Africa and the Middle East, and in regions of India and Portugal.

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  • Intermediate host : Freshwater snails of the Biomphalariagenus ---------------------->

  • Definitive host : humans are most important ------------------------------------>

  • Other definitive hosts : baboons, rodents and raccoons.

(Making a sad face will not change the fact

that you STILL are a definitive host, buddy !!! Nice Try Though)

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HOSTS Schistosomajaponicum

  • Intermediate host: Freshwater snails of the Oncomelania genus

  • Definitive host : humans are most important

  • Other definitive hosts: mammals including cats, dogs, goats, horses, pigs, rats and water buffalo.

(That raw-meat dress will not put you off the list of being the definitive host, lady!!!)

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  • Intermediate host : Freshwater snails of theBulinus genus

  • Definitive host: humans are most important.

  • Other final hosts are rarely baboons and monkeys.

(I thought that acting cool will put me off the list of definitive host but apparently, the parasite does not share the same thought as mine )

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  • The schistosomes are dioecious or in other words, the sexes are separate.

  • Adult worms are 10 to 20 mm in length

  • Male is larger and shorter than female

  • Male has shape of lamelliform or scalelike.

  • For reproduction : Male has gynaecophoric canal where the female resides in.

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Some More Pictures

Intestinal Schistosomiasis: eggs in the wall of the gut

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Eggs of Schistosomahaematobium

Schistosomahaematobium adult male

Schistosomahaematobium eggs in section of bladder

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Schistosomajaponicum egg

Schistosomajaponicum adult male and female

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Schistosomamansoni adult male and female

Eggs of Schistosomamansoni

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Life Cycle Picture

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Life Cycle in Words

  • Eggs are eliminated with feces or urine .  Under optimal conditions the eggs hatch and release miracidia , which swim and penetrate specific snail intermediate hosts . 

  • The stages in the snail include 2 generations of sporocysts and the production of cercariae .  Upon release from the snail, the infective cercariae swim, penetrate the skin of the human host , and shed their forked tail, becoming schistosomulae.

  • The schistosomulae migrate through several tissues and stages to their residence in the veins.Adult worms in humans reside in the mesenteric venules in various locations, which at times seem to be specific for each species .  For instance, S. japonicum is more frequently found in the superior mesenteric veins draining the small intestine , and S. mansoni occurs more often in the superior mesenteric veins draining the large intestine.

  • However, both species can occupy either location, and they are capable of moving between sites, so it is not possible to state unequivocally that one species only occurs in one location.  S. haematobium most often occurs in the venous plexus of bladder , but it can also be found in the rectal venules.  The females (size 7 to 20 mm; males slightly smaller) deposit eggs in the small venules of the  portal and perivesical systems. 

  • The eggs are moved progressively toward the lumen of the intestine (S. mansoni and S. japonicum) and of the bladder and ureters (S. haematobium), and are eliminated with feces or urine, respectively .  Pathology of S. mansoni and S. japonicumschistosomiasis includes: Katayama fever, presinusoidal egg granulomas, Symmers’ pipe stem periportal fibrosis, portal hypertension, and occasional embolic egg granulomas in brain or spinal cord. 

  • For a cool and way too awesome life cycle animation :

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Clinical Signs/Pathology For Schistosomamansoni/Japonicum

Acute (aka Katayama fever)

  • Skin rash

  • Chills

  • Fatigue

  • Fever

  • Ache

  • Cough


  • Bloody diarrhea

  • Loss of appetite and weight

  • Lethargy

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Clinical Signs/Pathology For Schistosomahaematobium


  • Urinary Tract (including the bladder)

  • Ulcers

  • bleeding into the urine

  • Scarring

  • Urogenital venous system


  • •Bladder cancer

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Clinical Signs Pictures

A 13-year-old boy with schistosomiasis : Hepatosplenomegaly, ascites, muscle atrophy, pyrexia, anaemia and haemorrhage from the gastrointestinal tract --------------->

The abdomen of an 11-year-old boy with intestinal schistosomiasis with the size and extent of the liver and spleen marked.

Two boys, victims of schistosomiasis showing typical distension of the abdomen

Infection Threat Distended Belly

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  • Detect the eggs in fecal sample

  • Serological and skin tests

  • Testing the urine

  • Blood sample

  • Ultrasonography.

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Control and Treatment

  • Praziquantel is effective against all species.

  • Oxamniquineis used exclusively to treat intestinal schistosomiasis in Africa and South America

  • Metrifonate is effective for the treatment of urinary schistosomiasis

  • Contaminated water should be avoided.

  • Control measures include sanitary disposal of sewage and destruction of snails.

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Long Term Treatment ?The Immune System is slacking off ?

  • Praziquantel is commonly used to treat schistosomiasis, and for travellers who have caught the disease whilst visiting an endemic region it represents a means of cure.

  • We normally think that if we have had a disease, that we will be immune to that same disease in the future.  But no !!!! Why ?

  • The ideal solution would be to develop a vaccine which would prevent the infection becoming established, and this has been the goal of schistosome research groups for several decades.  Given that no approved vaccine has yet emerged, why do we believe that this an achievable aim?

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Vaccines ? A Dream To Come or Forever Be a Myth ?

No vaccine is available currently because it’s hard to find an adequate animal model. The human schistosome infection cannot seem to be reproduced accurately in animals , and the mechanisms of protection have been found to differ among the various experimental models.

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Thanks God !!!There seems to a Light and Many Other Lights at The End of the Tunnel

  • However, on the bright side, there are vaccine candidates such as Glutathione-S-transferase, an enzyme found in the schistosomula and adult stages; paramyosin, a muscle protein found in the schistosomula and adult stages; triose-phosphate isomerase, an enzyme found in all stages; Sm23, a 23 kDa membrane antigen found on all stages; and fatty acid binding protein ((FABP)-14 or Sm14), a 14 kDa membrane antigen found in the schistosomula stage.

  • Other approaches include creating anti-idiotype vaccines against carbohydrate antigens, interfering with egg production, and blocking sex pairing.

  • In addition to these protein candidate antigens for vaccines, another interesting approach to schistosomiasis vaccine development involves the irradiation

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Economic Impact

  • An attempt is made to estimate the economic effects of schistosomiasis, a disease known to be endemic in 71 countries or islands with a total population of about 1 362 million persons, of whom approximately 124 905 800 are infected. These data are based on prevalence rates representing, for the most part, single stool or urine examinations; the actual number of cases is undoubtedly much greater. This analysis refers only to resource loss attributable to reduced productivity.

  • The annual loss from complete and partial disability is estimated to be US $445 866 945 in Africa, US $755 480 in Mauritius, US $16 527 275 in South-West Asia, US $118 143 675 in South-East Asia, and US $60 496 755 for the Americas. The total estimated annual world loss amounts to US $641 790 130 but this sum does not include the cost of public health programs, medical care, or compensation for illness.

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