Schistosomiasis

 S. mansoni and S. japonicum most frequently cause hepatosplenic disease






Etiology/Pathogenesis




• Infection occurs when cercariae (infectious larvae) leave intermediate host snail and penetrate skin of vertebrate host (in contaminated water)


Clinical Issues




• Each Schistosoma species associated with specific snail species, which determines geographic distribution
image 85% of infections are in sub-Saharan Africa

• Acute presentation (Katayama fever) is hypersensitivity reaction to schistosome antigens

• Chronic disease is secondary to tissue damage from inflammatory response to ova, not worms themselves

• 10% of patients progress to severe hepatic fibrosis
image Hepatic function preserved until late in disease course

• Laboratory tests
image Stool or urine examination for ova

image Serology to detect antischistosomal antibodies


Microscopic




• Portal fibrosis with partial or complete destruction of main branches of portal vein and sparing of arteries and ducts

• Granulomatous reaction to ova with variably present foreign body giant cells, eosinophils, mononuclear cells

• Ova have refractile shell and lateral spine

• Hematin pigment in portal and sinusoidal macrophages


Diagnostic Checklist




• Granulomatous hepatitis in patient from endemic area warrants search for ova

image
Ova and Granulomas
This expanded and markedly fibrotic portal area contains numerous granulomas with central ova image ; some are clearly embryonated. There is associated chronic inflammation, but eosinophils are not prominent in this case.


image
Embryonated Egg
This portal granuloma contains an embryonated egg with a lateral spine image .

image
Hematin Pigment
Macrophages in the portal tracts and sinusoids contain dark brown pigment, consistent with hematin, which is regurgitated by the flukes after metabolizing hemoglobin.

image
Calcified Eggs
Two calcified ova are present in a portal tract image, possibly in a small venule; the spines are not visible. In this case, a granulomatous reaction is not present. The lack of inflammation and calcification of the ova implies remote infection.


TERMINOLOGY


Synonyms




• Bilharziasis, snail fever, Katayama fever


Definitions




• Parasitic infection caused by trematodes (blood flukes) of genus Schistosoma
image 3 major species cause infection in humans: S. mansoni, S. haematobium, S. japonicum

– S. mansoni and S. japonicum more likely to cause disease in liver and bowel


ETIOLOGY/PATHOGENESIS


Life Cycle and Infection




• Infected humans/animals contaminate fresh water with eggs by urine or feces
• Eggs release miracidia, which penetrate snails

• Infection occurs when cercariae (infectious larvae) exit snail and penetrate skin of vertebrate host (in contaminated water)

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Apr 20, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Schistosomiasis

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