2Phylum Platyhelminthes – Class Trematoda General characters: Dorsoventrally flattened typically leaf shapedhave an oral and a ventral sucker used for attachment and movement.Bifurcate intestinecomplex life cycle with multiple hosts.mollusc is usually 1st intermediate hostdefinitive host is a vertebratemost are hermaphroditic except blood flukes.
7Blood 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 hostsDefinitive host: HumanIntermediate host: SnailReservoirs: monkeys, rodents, cats, dogs, cattle, horses, swine, wild mammalsThe human disease known as shistosomiasis , Bilharzia, BilhariaziasisIn 1852 the German parasitologist, Theodor Bilharz, made the first discovery of schistosomes (S. haematobium) while working in EgyptEggs are responsible for the pathology associated with infections
8Human Blood flukes: Three major species Schistosoma haematobiumSchistosoma japonicumSchistosoma mansoni
11Morphology: 1- All species roughly similar. 2- Sexes are separate (dioecious).3- size cm in length.3- Males short and wide, females long, thin.4- Female adults reside in gynecophoral canal formed by male body.
15Schistosoma haematobium Habitat: venules of the urinary bladderDisease: Urinary schistosomiasisEgg: Ellipsoidal withterminal spine.Diagnostic stageIntermediate hosts: are fresh water snails Bulinus
16Schistosoma mansoni Habitat: in venules of the large intestine Disease: intestinal schistosomiasisEgg: Ellipsoidal with lateral spineDiagnostic stageIntermediate hosts: are fresh water snailBiomphalaria
18Schistosoma japonicum Habitat: venules of the small intestineDisease: oriental schistosomiasisEgg:round with rudimentary spine laterallyDiagnostic stageIntermediate host: are fresh water snail Oncomelania
23Symptoms:The first symptom is a localized dermatitis, often observed following cercarial penetration of the skinIt 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 phaseChronic phase
241- The migration phase (from penetration to egg production) There are often no symptomsIt 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.
25Chronic Disease Hepatosplenic Schistosomiasis : S. mansoni and S. japonicumSeveral years after initial infectionGranulomas form within the liver and biliary treeHepatosplenomegalyportal hypertension – liver failureIntestinal SchistosomiasisAdults migrate to intestinal wallLay eggs which migrate into intestinal lumen and out into stoolSevere anemia from chronic GI blood loss
26Chronic Disease S. haematobium Several years after infection Adults migrate to small venules around the bladder and ureterEggs are deposited into surrounding tissue and penetrate out into bladderCauses calcifications where eggs are trappedCharacterized by hematuriaLeads to cancer of bladder
27Granuloma 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.Schistosoma egg in the liver : granuloma formationIntestinal schistosomiasis: eggs in the wall of the gut
29Laboratory 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.
30Swimmers Itch:An interesting aspect of schistosome biology concerns cercarial dermatitis or swimmer’s itchThe 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 rashSince humans are not suitable definitive hosts for these flukes, the cercariae do not normally enter the blood stream and matureInstead, after penetrating the skin, they are destroyed by the victim’s immune responseAllergenic material released from dead and dying cercariae produce a localized inflammatory reaction
31Cercarial Dermatitis (Swimmer’s Itch) Due to cercaria of avian schistosomesAvian (bird) schistosomiasis